ALBERT

Description: Females of many animal species seek mating opportunities with multiple males, despite being able to obtain sufficient sperm to father their offspring from a single male. In animals that live in stable social groups, females often choose to mate outside their group resulting in extra-group paternity (EGP). One reason proposed to explain female choice for extra-group males is to obtain compatible genes, for example, in order to avoid inbreeding depression in offspring. The benefits of such extra-group paternities could be substantial if they result in fitter, outbred offspring. However, avoiding inbreeding in this way could be costly for females, for example, through retaliation by cuckolded males or through receiving aggression while prospecting for extra-group mating opportunities. We investigate the costs and benefits of EGP in the banded mongoose Mungos mungo , a cooperatively breeding mammal in which within-group mates are sometimes close relatives. We find that pups born to females that mate with extra-group males are more genetically heterozygous are heavier and are more likely to survive to independence than pups born to females that mate within their group. However, extra-group matings also involve substantial costs as they occur during violent encounters that sometimes result in injury and death. This appears to lead femalebanded mongooses to adaptively adjust EGP levels according to the current risk of inbreeding associated with mating within the group. For group-living animals, the costs of intergroup interactions may help to explain variation in both inbreeding rates and EGP within and between species.

Description: Many species living in developed areas adjust the timing of their activity and habitat selection to avoid humans, which may reduce their risk of conflict, including vehicle collisions. Understanding the behavioral adaptations to vehicles exhibited by species that thrive in urban areas could improve the conservation of many species that are threatened by road-caused mortality. We explored these behaviors using the seasonal distribution of 80 road-killed coyotes ( Canis latrans ) collected by civic employees and by comparing the activity patterns (step lengths) and road crossings made by 19 coyotes fitted with GPS collars with 3-h fix rates, 7 of which were killed in vehicle collisions. Coyotes were collected on roads most often in spring and fall, which corresponded to the most rapid changes in day length in our northern study area and when collared road-killed coyotes were more active during rush hour. Among collared coyotes, those that were killed on roads were most active and crossed roads most frequently at dusk. By contrast, surviving animals were most active and crossed roads most often near midnight year round and surprisingly, exhibited less avoidance of roads than did road-killed coyotes. Our results suggest that risk of vehicle collision is lower for coyotes that restrict the times at which they cross roads but some coyotes do not or cannot. Such behavioral flexibility to adapt to the timing of human activity relative to exogenous cues such as dawn and dusk may contribute to differences both among and within wildlife species in rates of coexistence with humans.

Description: Group living in animals is a well-studied phenomenon, having been documented extensively in a wide range of terrestrial, freshwater, and marine species. Although social dynamics are complex across space and time, recent technological and analytical advances enable deeper understanding of their nature and ecological implications. While for some taxa, a great deal of information is known regarding the mechanistic underpinnings of these social processes, knowledge of these mechanisms in elasmobranchs is lacking. Here, we used an integrative and novel combination of direct observation, accelerometer biologgers, and recent advances in network analysis to better understand the mechanistic bases of individual-level differences in sociality (leadership, network attributes) and diel patterns of locomotor activity in a widespread marine predator, the lemon shark ( Negaprion brevirostris ). We found that dynamic models of interaction based on Markov chains can accurately predict juvenile lemon shark social behavior and that lemon sharks did not occupy consistent positions within their network. Lemon sharks did however preferentially associate with specific group members, by sex as well as by similarity or nonsimilarity for a number of behavioral (nonsimilarity: leadership) and locomotor traits (similarity: proportion of time swimming "fast," mean swim duration; nonsimilarity: proportion of swimming bursts/transitions between activity states). Our study provides some of the first information on the mechanistic bases of group living and personality in sharks and further, a potential experimental approach for studying fine-scale differences in behavior and locomotor patterns in difficult-to-study organisms.

Description: Sexually selected traits are often driven to costly extremes by persistent directional selection. Energy acquisition and allocation can therefore influence variation in traits subject to both precopulatory and postcopulatory sexual selection, though the later have received much less attention. We tested the condition dependence of sperm morphology, sperm count, and fertilization success in a promiscuous lizard ( Anolis sagrei ) by 1) collecting sperm samples from wild males that varied naturally in body condition, 2) experimentally altering the body condition of captive males through dietary restriction, and 3) analyzing genetic paternity data from competitive mating trials between captive males that differed in body condition. In both wild and captive males, the length of the sperm midpiece decreased with body condition. Experimental food restriction decreased sperm production, decreased length of the sperm head, increased length of the sperm midpiece, and increased variance in sperm morphology within individuals. When restricted to a single copulation, males on high-intake diets exhibited a slight but nonsignificant fertilization advantage. Reanalysis of a previous experiment in which high- and low-condition males were sequentially allowed to copulate ad libitum for 1 week revealed a significant fertilization bias in favor of high-condition males. When controlling for mean treatment effects on the proportion of offspring sired and on sperm phenotypes, multiple regression revealed negative correlations between fertilization success and sperm head length, midpiece length, and sperm count. Collectively, our results suggest that condition-dependent fertilization success in A. sagrei may be partially mediated by underlying condition dependence of sperm morphology and sperm count.

Description: The postfledging dependence period (PFDP) is a crucial stage in the development of altricial birds. This period is regulated by parental investment, in terms of food provisioning and protection, and the demands of young associated with their development and physical condition. We examine the relative role of parental investment, food provisioning, and offspring decisions on the PFDP regulation in the Spanish imperial eagle ( Aquila adalberti ) by comparing the PFDP timing among young from non-manipulated territories, food supplemented territories, and birds translocated by hacking methods in the absence of adults and with ad libitum food supply. We found that extra food homogenized the nutritional condition of young and reduced the length of the first stage of PFDP, which is related to flight development and thus dependent on body condition. However, hacked birds did not reduce this stage despite ad libitum food, likely due to the lack of parental stimulus to develop advanced flights. Although the presence of adults might accelerate young becoming independent, hacked birds did not extend significantly the whole PFDP and all birds eventually started dispersal. Thereby, the PFDP regulation was primarily under offspring control, and modulated secondarily by parental effects independently of food provisioning and laying date. The length of this period seems to be constrained mainly by the inherent benefits of early dispersal on ultimate fitness in accordance with ontogenic hypotheses. In addition, hacking was shown to be an effective translocation method when properly used, without negative drawbacks for young development during the PFDP.

Description: In antagonistic encounters, the primary decision to be made is to fight or not. Animals may then possess adaptations to assess fighting ability in their opponents. Previous studies suggest that humans can assess strength and fighting ability based on facial appearance. Here we extend these findings to specific contests by examining the perception of male faces from paired winners and losers of individual fights in mixed martial arts sporting competitions. Observers, unfamiliar with the outcome, were presented with image pairs and asked to choose which of the 2 men was more likely to win if they fought while other observers chose between the faces based on masculinity, strength, aggressiveness, and attractiveness. We found that individuals performed at rates above chance in correctly selecting the winner as more likely to win the fight than the loser. We also found that winners were seen to be more masculine, stronger, and more aggressive than losers. Finally, women saw the winners as more attractive than the losers. Together these findings demonstrate that 1) humans can predict the outcome of specific fighting contests based on facial cues, 2) perceived masculinity and strength are putative cues to fighting success available from faces, and 3) facial cues associated with successful male–male competition are attractive to women.

Description: Assessing an opponent’s strength is an important component of attack strategies in territorial combats between males. Body size is often considered to directly influence an individual’s strength, but other honest visual signals may also affect the assessment of opponents. Among such visual signals are the so-called egg-spots, a conspicuous ovoid marking on the anal fin of male haplochromine cichlid fishes, made up of carotenoid-containing and other pigment cells. It has long been assumed that egg-spots are mainly relevant in courtship and spawning behavior, and previous work has focused primarily on their function in intersexual selection. Recently, however, both body size and egg-spots have been suggested to play a role in male–male interactions. To test whether egg-spots function in female choice or whether egg-spots and/or body size function as a predictor of strength and the subsequent attack strategy in male–male interactions, we performed a series of behavioral experiments in the haplochromine cichlid Astatotilapia calliptera . The trials revealed a limited involvement of egg-spots in female choice, yet a much stronger influence in male interactions. Territorial males combined information from the strength assessment based on body size and egg-spots to adopt their attack strategies. They launched more attacks against the larger intruder with many egg-spots compared with the smaller intruder without or with fewer egg-spots. Our study provides evidence that egg-spots serve as honest visual signal and that the level of asymmetries in egg-spot pattern and body size determines the relative impact of each trait in strength assessment.

Description: Evaluating the costs and benefits of dispersal on individual life history is critical to understanding its importance to ecology and evolution. In feral horses ( Equus ferus caballus ), females may permanently move among breeding groups (bands) during their lifetime (termed social dispersal). Here, we assess costs and benefits of adult female social dispersal using 7 years of movement and life history data from an individual-based study of feral horses on Sable Island. Using path and survival analyses, we explored relationships between social dispersal, female reproduction, and survival of offspring. Dispersal negatively correlated with a female’s next reproduction (probability to produce a living foal that was observed during our summer census) and reproductive success (RS) over the longer term (probability of producing foals in subsequent years). Females that dispersed had longer latency before next reproduction than nondispersing (philopatric) females. We could not measure costs in terms of induced abortions or neonatal survival, but we observed no evidence of infanticide during our summer censuses. Furthermore, overwinter survival of foals to 3 years of age was not affected by either dispersal of its mother before conception or as pregnant. Despite a 10% higher rate for foals dispersing with mothers to survive to 3 years compared with those of philopatric females, the difference was not statistically significant. Overall, our results suggest that dispersing individuals have lower RS that may be a cost of social dispersal on future reproduction.

Description: Large mammalian carnivores create areas perceived as having high and low risk by their ungulate prey. Human activities can indirectly shape this landscape of fear by altering behavior and spatial distribution of carnivores. We studied how red deer perceive the landscape of fear in an old-growth forest system (Białowieza Primeval Forest, Poland) both at large and fine spatial scale. Camera traps were placed at locations with and without tree logs (fine-scale risk factor) and at different distances from the core of a wolf territory and human settlements (large-scale risk factor). Red deer avoided coming close to large tree logs and increased their vigilance levels when they were present in close vicinity. The strength of these effects depended on the distance to the wolf core area; deer perceived tree logs as more risky when wolves were more often present. Hence, tree logs inside wolf core areas create fine-scale patches of fear with reduced deer browsing pressure, thereby enhancing chances for successful tree recruitment. Human presence shapes this landscape of fear as wolf core areas are located far from human settlements. This "human shadow" on predator–prey interactions is therefore an important component that should be taken into account in human-dominated landscapes.

Description: Why do females faced with the same array of potential mates often select different males? Variation in choosiness, defined as investment in mate search, is an important potential source of variation in mating decisions. Experimental work suggests such variation is driven by the costs of searching, but data from natural populations are scarce and few studies have addressed explicitly the counteracting benefits expected from search investment. We tracked male visitation behavior of free-ranging females on a lek of lance-tailed manakins ( Chiroxiphia lanceolata ) using automated telemetry at dispersed male display sites. We assessed relationships of female age, experience, body condition, and parasite load with variation in choosiness, quantified as males visited, number of visits, and visit duration. Young females visited more males and made more total visits before choosing a mate, whereas older females conducted longer visits for first nests of the year. Renesting females searched less, but the few monitored females mating faithfully between years nevertheless sampled several males. We found little support for effects of condition on choosiness. Results suggest females sample more widely when they lack information about the distribution of available mates. Though previous work in the study population has shown both female preference for and offspring fitness benefits from heterozygous sires, genetic tests of paternity revealed choosier females did not choose more heterozygous mates. Females’ investment in mate search varied in relation to their own age and within-year experience, but mate search investment did not independently determine variation in choice among individuals.

Description: Urban animals often show differences in aggression relative to their rural counterparts, but the ultimate and proximate origins of these differences are poorly understood. Here, we compared urban and rural song sparrows ( Melospiza melodia ), a species for which higher levels of aggression in urban populations have previously been reported. First, we confirmed elevated territorial aggression levels in urban birds relative to rural birds over multiple years. To begin to identify the environmental variables contributing to these differences, we related aggression to features of the social and physical environment, specifically population density and the availability of suitable nesting vegetation. Population distribution and the availability of suitable nest vegetation were not correlated with territorial aggression levels. Subsequently, we conducted a food supplementation experiment to determine whether potential differences in the relative availability of food between the 2 habitats might drive differences in aggression. Food supplementation increased territorial aggression significantly, particularly in rural birds. Thus, it appears that the availability of food could play a role in determining territorial aggression in song sparrows. The specific combination of these features found in urban areas may cause the increased levels of territorial aggression seen in these populations.

Description: A critical question in the study of the evolution of cognition and the brain concerns the extent to which variation in cognitive processes and associated neural mechanisms is adaptive and shaped by natural selection. In order to be available to selection, cognitive traits and their neural architecture must show heritable variation within a population, yet heritability of cognitive and neural traits is not often investigated in the field of behavioral ecology. In this commentary, we outline existing research pertaining to the relative influences of genes and environment in cognitive and underlying neural trait variation, as well as what is known of their heritable genetic architecture by focusing on several cognitive traits that have received much attention in behavioral ecology. It is important to demonstrate that cognitive traits can respond to selection, and we advocate for an increased emphasis on investigating trait heritability for enhancing our understanding of the ecological, genetic and neurobiological mechanisms that have shaped interspecific and intraspecific variation in cognitive traits.

Description: Two recent observations in behavioral biology have sparked great interest and have already yielded many novel and intriguing insights. Bacteria appear to live lives of unforeseen behavioral complexity, and the consistent behavioral variation among individual animals is often not "noise" but turns out to be a highly relevant ecological and evolutionary feature in itself. Research covering these 2 phenomena has proceeded largely in isolation, and the rich behavioral lives of bacteria have not yet been studied with consistent interindividual behavioral differences in mind. Yet, the parallels between animal and bacterial behavior that are increasingly being uncovered, as well as the particular characteristics of bacteria, point toward a new approach in the study of consistent individual variation in behavior. Using bacteria can bring fruitful opportunities to the field and allows researchers to address questions that are very difficult to pursue using animal model systems. Notwithstanding a few challenges, bacteria can provide an alternative study system that may elucidate several evolutionary and ecological aspects of consistent individual behavioral variation.

Description: The fitness and survival of organisms ultimately depend on their feeding. Therefore, foraging behaviors should be selected to maximize cost-benefit ratio. Wind may restrict and modify animal movements increasing the cost of foraging, especially when the animal carries resources that intercept wind. We quantified the effect of wind on the foraging of leaf-cutting ants and evaluated whether this effect varies with 1) leaf fragment traits, such as area, mass, and shape, and 2) the characteristics of the foraging trail system. We also tested whether these ants show a short-term response to wind by selecting loads with characteristics that reduce wind interception, and a long-term response, by arranging the spatial design of the trail system in a way that reduces that effect. We found that in windy conditions, the speed of loaded ants was reduced by 55%, and ants were blown off the trail 28 times more than in windless conditions. However, wind only affected ants walking along trails that were perpendicular to wind direction or parallel upwind. Wind effect increased with area, mass, and shape of loads. At the short term, ants reduced the negative effect of wind by selecting smaller, lighter, or more elongated loads. However, trails showed no particular spatial distribution in relation to wind direction. This is the first study that quantifies the negative consequences of wind on leaf-cutting ants’ foraging and reports behaviors that can reduce this effect. Our work illustrates how short-term behavioral responses can mitigate the negative effect of an understudied environmental factor on ant foraging.

Description: The temporal partitioning hypothesis suggests that the evolution of different diel activity rhythms in animals might facilitate the coexistence between prey and predators. However, the temporal shift of habitat use induced by predation has rarely been observed. The study of such a mechanism is particularly relevant for introduced species because it might explain how native species can persist or decline in response to the presence of alien species. The introduction of fish into ponds inhabited by amphibians has severe consequences for their occurrence and abundance. Fish particularly affect an alternative newt phenotype, the paedomorph, which does not undergo metamorphosis and maintains larval traits such as gills at the adult stage. In a laboratory design, we assessed the diel patterns of habitat use in the 2 distinct morphological phenotypes of palmate newt ( Lissotriton helveticus ) in the presence or absence of goldfish ( Carassius auratus ). Both newt phenotypes avoided a risky habitat more in the presence than in the absence of fish. This habitat shift was more pronounced during the daytime (i.e., when the risk could be considered higher for the newts) than during nighttime. However, in contrast to metamorphs, paedomorphs showed less adaptive changes according to temporal risk and remained in their shelter for most of the time. Temporal and habitat partitioning at the diel scale between native and alien species might promote their coexistence, but diel change can also imply a cost in the overall reduction of the time allocated to essential activities, showing that species interactions remain complex.

Description: Translocation is an important conservation management tool. However, not all individuals are equally suited to translocation, and temperament traits (e.g., boldness, reactivity, exploration, sociability, and aggression) are likely to influence survival in a new environment. A few empirical studies have examined the consequences of personality differences on captive-bred translocated animals, but this has not been done for wild-caught animals. We compared behavioral responses to trapping, processing, holding, and release for 56 wild common brushtail possums ( Trichosurus vulpecula ). Twenty individuals were captured twice, once to attach radio-tracking collars, the second time (2 weeks later) for the translocation. Consistency of behavioral responses was compared between capture events and radio-tracking allowed estimates of pretranslocation home range, rest site selection, and foraging behavior. Survivors ( n = 10 survivors, 5 months later) were individuals showing the most fear or emotional reactivity during holding (less likely to have slept, eaten, defecated, or nested) and those that had the smallest home ranges and selected the safest den sites in their original habitat. Conversely, the greatest increase in body mass was recorded for individuals that had demonstrated "unsafe" behavior in their original habitat. To our knowledge, this is the first time this type of behavioral screening during handling and holding prior to release as part of a translocation has been undertaken. These methods have broad applicability for screening potential translocation candidates and are easily translated to a range of threatened and vulnerable animal species.

Description: The distribution and abundance of food resources are among the most important factors that influence animal behavioral strategies. Yet, spatial variation in feeding habitat quality is often difficult to assess with traditional methods that rely on extrapolation from plot survey data or remote sensing. Here, we show that maximum entropy species distribution modeling can be used to successfully predict small-scale variation in the distribution of 24 important plant food species for chimpanzees at Gombe National Park, Tanzania. We combined model predictions with behavioral observations to quantify feeding habitat quality as the cumulative dietary proportion of the species predicted to occur in a given location. This measure exhibited considerable spatial heterogeneity with elevation and latitude, both within and across main habitat types. We used model results to assess individual variation in habitat selection among adult chimpanzees during a 10-year period, testing predictions about trade-offs between foraging and reproductive effort. We found that nonswollen females selected the highest-quality habitats compared with swollen females or males, in line with predictions based on their energetic needs. Swollen females appeared to compromise feeding in favor of mating opportunities, suggesting that females rather than males change their ranging patterns in search of mates. Males generally occupied feeding habitats of lower quality, which may exacerbate energetic challenges of aggression and territory defense. Finally, we documented an increase in feeding habitat quality with community residence time in both sexes during the dry season, suggesting an influence of familiarity on foraging decisions in a highly heterogeneous landscape.

Description: Despite parents are equally related to all of their progeny, they may differentially invest in offspring that provide the highest fitness return. Sons and daughters can differ in reproductive value, especially in species where fitness is predicted by the expression of sexually selected traits. In many birds, offspring plumage coloration functions as a honest signal of individual quality, thus allowing parents to differentially invest in offspring of either sex accordingly. Here, we tested whether parents allocate different amounts of food depending on plumage color of their male and female offspring. As a model, we used the barn swallow ( Hirundo rustica ), a species where large among- and within-brood variation in ventral plumage color exists and male reproductive success varies according to ventral plumage coloration. We recorded the proportion of feedings obtained and body mass variation by dyads of same-sex and similar-sized nestlings subjected to either experimental darkening of their ventral plumage color or to a sham treatment. Plumage darkening enhanced food provisioning and body mass gain of males but not of females. Because darker ventral coloration is associated with larger reproductive success in male barn swallows, these results suggest that parents tune their effort toward more valuable male offspring that are likely to provide the greatest fitness returns. Our study thus suggests that parents are selected to differentially invest in offspring of either sex according to a trait expressed in early life, which is relevant to intrasexual competition for access to mates at sexual maturity.

Description: The iconic red hourglass of the black widow spiders (genus Latrodectus ) is traditionally considered an aposematic signal, yet experimental evidence is lacking. Here, we present data that suggest that black widow coloration may have evolved to be an aposematic signal that is more conspicuous to their vertebrate predators than to their insect prey. In choice experiments with wild birds, we found that the red-and-black coloration deters potential predators: Wild birds were ~3 times less likely to attack a black widow model with an hourglass than one without. Using visual-system appropriate models, we also found that a black widow’s red-and-black color combo is more apparent to a typical bird than a typical insect. Additionally, an ancestral reconstruction reveals that red dorsal coloration is ancestral in black widows and that at some point some North American widows lost their red dorsal coloration. Behaviorally, differences in red dorsal coloration between 2 North American species are accompanied by differences in microhabitat that affects how often a bird will view a black widow’s dorsal region. All observations are consistent with a cost–benefit trade-off of being more conspicuous to predators than to prey. We suggest that limiting detection by prey may help explain why red and black aposematic signals occur frequently in nature.

Description: While conducting a toxicity assessment of the antidepressant paroxetine (Paxil®), in wild-derived mice ( Mus musculus ), we observed that exposed dams (P 0 ) produced female biased litters (32:68 M:F). Though numerous experimental manipulations have induced sex ratio bias in mice, none have assessed the fitness of the offspring from these litters relative to controls. Here, we retrospectively analyze experimentally derived fitness data gathered for the purpose of toxicological assessment in light of 2 leading hypothesis (Trivers–Willard hypothesis [TWH] and cost of reproduction hypothesis [CRH]), seeking to test if this facultative sex ratio adjustment fits into an adaptive framework. Control F 1 males were heavier than F 1 females, but no differences in mass were detected between exposed F 1 males and females, suggesting that exposed dams did not save energy by producing fewer males, despite producing 29.2% lighter litters relative to controls. F 1 offspring of both treatments were released into seminatural enclosures where fitness was quantified. In enclosures, the relative reproductive success of F 1 -exposed males (compared with controls) was reduced by ~20% compared with the relative reproductive success of F 1 -exposed females. Thus, exposed dams increased their fitness by adjusting litters toward females who were less negatively affected by the exposure than males. Collectively, these data provide less support that the observed sex ratio bias results in energetic savings (CRH), and more support for the TWH because fitness was increased by biasing litters toward female offspring. These mammalian data are unique in their ability to support the TWH through the use of relevant fitness data.

Description: Understanding how seabirds and other central place foragers locate food resources represents a key step in predicting responses to changes in resource abundance and distribution. Where prey distributions are unpredictable and ephemeral, seabirds may gain up-to-date information by monitoring the direction of birds returning to the colony or by monitoring the foraging behavior of other birds through local enhancement. However, search strategies based on social information may require high population densities, raising concerns about the potential loss of information in declining populations. Our objectives were to explore the mechanisms that underpin effective search strategies based on social information under a range of population densities and different foraging conditions. Testing relevant hypotheses through field observation is challenging because of limitations in the ability to manipulate population densities and foraging conditions. We therefore developed a spatially explicit individual-based foraging model, informed by data on the movement and foraging patterns of seabirds foraging on pelagic prey, and used model simulations to investigate the mechanisms underpinning search strategies. Orientation of outbound headings in line with returning birds enables departing birds to avoid areas without prey even at relatively low population densities. The mechanisms underpinning local enhancement are more effective as population densities increase and may be facilitated by other mechanisms that concentrate individuals in profitable areas. For seabirds and other central place foragers foraging on unpredictable and ephemeral food resources, information is especially valuable when resources are spatially concentrated and may play an important role in mitigating poor foraging conditions.

Description: Experiments designed to quantify the effects of increasing numbers of carers on levels of offspring care are rare in cooperative breeding systems, where offspring are reared by individuals additional to the breeding pair. This paucity might stem from disagreement over the most appropriate manipulations necessary to elucidate these effects. Here, we perform both carer removal and brood enhancement experiments to test the effects of numbers of carers and carer:offspring ratios on provisioning rates in the cooperatively breeding chestnut-crowned babbler ( Pomatostomus ruficeps ). Removing carers caused linear reductions in overall brood provisioning rates. Further analyses failed to provide evidence that this effect was influenced by territory quality or disruption of group dynamics stemming from the removals. Likewise, adding nestlings to broods caused linear increases in brood provisioning rates, suggesting carers are responsive to increasing offspring demand. However, the 2 experiments did not generate quantitatively equivalent results: Each nestling received more food following brood size manipulation than carer removal, despite comparable carer:offspring ratios in each. Following an at-hatching split-design cross-fostering manipulation to break any links between prehatching maternal effects and posthatching begging patterns, we found that begging intensity increased in larger broods after controlling for metrics of hunger. These findings suggest that manipulation of brood size can, in itself, influence nestling provisioning rates when begging intensity is affected by scramble competition. We highlight that carer number and brood size manipulations are complimentary but not equivalent; adopting both can yield greater overall insight into carer effects in cooperative breeding systems.

Description: Dispersal affects the social contexts individuals experience by redistributing individuals in space, and the nature of social interactions can have important fitness consequences. During the vagrancy stage of natal dispersal, after an individual has left its natal site and before it has settled to breed, social affiliations might be predicted by opportunities to associate (e.g., distance in space and time between natal points of origin) or kin preferences. We investigated the social structure of a population of juvenile great tits ( Parus major ) and asked whether social affiliations during vagrancy were predicted by 1) the distance between natal nest-boxes, 2) synchrony in fledge dates, and 3) accounting for spatial and temporal predictors, whether siblings tended to stay together. We show that association strength was affected predominantly by spatial proximity at fledging and, to a lesser extent, temporal proximity in birth dates. Independently of spatial and temporal effects, sibling pairs associated more often than expected by chance. Our results suggest that the structure of the winter population is shaped primarily by limits to dispersal through incomplete population mixing. In addition, our results reveal kin structure, and hence the scope for fitness-related interactions between particular classes of kin. Both spatial-mediated and socially mediated population structuring can have implications for our understanding of the evolution of sociality.

Description: Cultural transmission in nonhuman animals is often sex biased, with females more frequently or efficiently learning cultural behaviors than males. The evolutionary origins of sex-biased cultural transmission have been a mystery, though it has been proposed that female offspring may gain greater reproductive benefit from cultural traits than sons—the "disparate benefits" hypothesis. I propose a different, "uniparental teaching," hypothesis where sex-biased transmission evolves in uniparental species if mothers teach, that is, invest in their offsprings’ learning. I show, with theoretical models, that mothers evolve to invest more in teaching daughters than sons because teaching daughters results in greater inclusive fitness benefits. Teaching a son gives him a reproductive benefit for one generation. However, I show that because daughters may teach future generations, teaching a daughter can be a better long-term investment. I also model the disparate benefits hypothesis and show that the uniparental teaching hypothesis better fits the empirical patterns of sex-biased transmission in the well-studied example of "sponging" in bottlenose dolphins. Uniparental teaching may also explain sex-biased transmission in other species, including chimpanzees. My findings suggest that controversial mechanisms of cultural transmission in nonhumans, such as teaching, may be inferred from population-level patterns of transmission even when it is difficult to observe transmission directly in the field or laboratory.

Description: Iteroparous organisms face a trade-off between reproduction and survival, but knowledge of whether how and when costs of long-term increases in workload are paid is scant. We increased locomotion costs for a whole year by equipping male great tits with a backpack during breeding, removing the backpacks 1 year later. We applied 3 different treatments: control (without backpack), light ("empty" backpack, 0.1g), and heavy ("full" backpack, 0.9g, ~5% of body mass). Backpacks were administered in 3 cohorts, and we monitored effects on mass of nestlings and the male, wing length, reproduction, and survival. Added mass had a negative effect on nestling mass in both the starting year of the experiment and 1 year later, but not on production of fledglings or recruits. In winter and the next breeding season, males equipped with heavy backpacks had a higher (net) body mass and had shorter third primary feathers than the other 2 groups. Heavy backpack males were less likely to sleep in a nest box in winter. Nest boxes are optimal roosting sites, and we interpret this finding as a treatment effect on success in competition over this resource. However, there was no effect of the manipulation on survival. Overall, we found no long-term fitness consequences, and we discuss possible explanations and implications for the "starvation–predation theory" of optimal body mass. However, we found short-term effects of carrying extra weight suggesting that behavioral studies using small devices should consider the effects of equipping small non-migratory passerines with devices such as transmitters.

Description: Behavior is usually the first line of defense against parasites. Antiparasite behaviors, such as grooming, or outright avoidance, have been shown to reduce the risk of parasitism in a wide variety of host–parasite systems. However, despite the central importance of antiparasite behavior, little is known about the extent to which prior exposure to parasites improves effectiveness. Here, we report the results of a 2-year study designed to test whether exposure to parasites can "prime" behavior, loosely analogous to priming of the immune system. We tested whether preening improves with experience by infesting captive-bred rock pigeons ( Columba livia ) with 2 common species of rock pigeon feather lice. We infested "primed" birds in Years 1 and 2 of the study and "nonprimed" birds only in Year 2. Birds with lice preened about a third more, on average, than birds without lice. Birds subsequently cleared of lice resumed preening at the same rate as birds that never had lice. Thus, our results confirm that preening is an inducible, reversible defense that is partly triggered by the presence of lice. Surprisingly, primed birds did not differ significantly from nonprimed birds in the overall rate or the efficacy of preening. Primed and nonprimed birds preened at similar rates and had similar numbers of lice at the end of the study. Our results therefore provide little evidence that antiparasite behavior improves with experience, at least in the case of preening as a defense against feather lice.

Description: Acoustic communication signals are often involved in mate-choice decisions. The decision for the best mating partner can become difficult when the available parameters of a signal are not positively correlated. Rational choice theory predicts that animals assign each signal a fixed value on a single dimension. The probability of choosing one signal over the other should be a monotonic function of the respective values and result in transitive choices. A violation of transitivity in choice behavior would suggest comparative rather than absolute decision making. Here, we tested the transitivity of preferences of female crickets for male calling songs. We conducted a series of binary choice experiments and compared their outcome to female preferences measured in no-choice experiments. To test transitivity, every choice pair had to differ in 2 parameters of the calling song. The parameter pairs used were 1) pulse rate and sound intensity, 2) chirp rate and sound intensity, and 3) pulse rate and chirp rate. The results revealed that females acted transitively if chirp rate and sound intensity or pulse rate and chirp rate of the patterns were varied. But females violated transitivity if pulse rate and sound intensity of signals differed as they mostly chose the louder pattern, although it was less attractive in the no-choice situation. This implies that sound intensity was weighted differently by females in the decision process in no-choice and choice experiments. The violation of transitivity suggests a comparative evaluation of available signals by female crickets.

Description: Ecological conditions are expected to have an important influence on individuals’ investment in cooperative care. However, the nature of their effects is unclear: both favorable and unfavorable conditions have been found to promote helping behavior. Recent studies provide a possible explanation for these conflicting results by suggesting that increased ecological variability, rather than changes in mean conditions, promote cooperative care. However, no study has tested whether increased ecological variability promotes individual-level helping behavior or the mechanisms involved. We test this hypothesis in a long-term study population of the cooperatively breeding banded mongoose, Mungos mungo , using 14 years of behavioral and meteorological data to explore how the mean and variability of ecological conditions influence individual behavior, body condition, and survival. Female body condition was more sensitive to changes in rainfall leading to poorer female survival and pronounced male-biased group compositions after periods of high rainfall variability. After such periods, older males invested more in helping behavior, potentially because they had fewer mating opportunities. These results provide the first empirical evidence for increased individual helping effort in more variable ecological conditions and suggest this arises because of individual differences in the effect of ecological conditions on body condition and survival, and the knock-on effect on social group composition. Individual differences in sensitivity to environmental variability, and the impacts this has on the internal structure and composition of animal groups, can exert a strong influence on the evolution and maintenance of social behaviors, such as cooperative care.

Description: Reduction of predation risk represents the most likely explanation for the evolution of group-living among the anthropoid primates. Obligate sociality leads to increased competition for resources, meaning that animals may face a trade-off between safe positions within the troop and increased foraging efficiency. Dominance has been proposed to be a major factor influencing spatial position within primate troops, but it is also possible that animals can improve their spatial position using social strategies, such as grooming. In many species, dominance rank and social preference (as expressed through grooming) are confounded. In our study population of vervet monkeys, however, dominance does not underpin social preference, enabling us to test whether 1) more sociable vervets experience reduced exposure to predation risk, as indexed by vigilance, and 2) that dominant animals accepted increased risk in order to forage at the front of the troop. We collected spatially explicit data on the individual locations of members of 2 troops at predetermined times over a 4-month period. We constructed bounded Voronoi tessellations for each temporal snapshot, with the area of each animal’s "tile" identifying its "domain of danger." We also collected data on time spent vigilant and foraging, dominance rank, and grooming behavior. We found no effect of dominance, but animals with larger grooming networks were less exposed to predation risk, from which they benefitted through both reduced vigilance and increased foraging time. We interpret these results in the light of current debates about the ways in which sociality affects fitness.

Description: The high frequency of same-sex sexual behaviors (SSB) in free-ranging animals is an evolutionary puzzle because fitness benefits are often unclear in an evolutionary context. Moreover, the physiological and genetic underpinnings of SSB remain unclear. We exploited an extraordinary natural experiment to examine the impact of environmental factors (local sex ratio [SR]) and testosterone (T) levels on SSB in a dense population of Hermann’s tortoises monitored for 7 years. Under the combination of high density and extremely skewed SR (~50 females, 〉1000 males), males courted and mounted other males more frequently than females. They even exhibited extravagant sexual behaviors, attempting to copulate with dead conspecifics, empty shells, and stones. T levels remained within the species’ normal range of variation. SSB was not observed in other populations where SR is not, or less skewed, and where density is lower. This study reports the first natural example of a "prison effect," whereby a high population density combined with female deprivation triggered SSB as a mere outlet of sexual stimulation. More generally, it supports the hypothesis that SSB can be a nonadaptive consequence of unusual proximate factors rather than reflecting physiological disorders.

Description: In animal contests, individuals respond plastically to the phenotypes of the opponents that they confront. These "opponent"—or "indirect"—effects are often repeatable, for example, certain opponents consistently elicit more or less aggressiveness in others. "Personality" (repeatable among-individual variation in behavior) has been proposed as an important source of indirect effects. Here, we repeatedly assayed aggressiveness of wild-caught adult male field crickets Gryllus campestris in staged dyadic fights, measuring aggressiveness of both contestants. Measurements of their personality in nonsocial contexts (activity and exploration behavior) enabled us to ask whether personality caused indirect effects on aggressiveness. Activity, exploration, and aggressiveness were positively associated into a behavioral syndrome eliciting aggressiveness in conspecifics, providing direct evidence for the role of personality in causing indirect effects. Our findings imply that a multivariate view of phenotypes that includes indirect effects greatly improves our ability to understand the ecology and evolution of behavior.

Description: Individuals that retain their former partners often perform better than conspecifics that switch partners. This may be due to high-quality individuals being more faithful to their partners and more productive. Investigations of the fitness benefits of mate retention that also control for potential confounding effects of individuals are scarce. We studied the influence of mate retention and breeding experience on breeding performance of the hair-crested drongo ( Dicrurus hottentottus ) by carrying out both cross-sectional and longitudinal analyses. Pairs with longer pair-bond duration did not fledge more young or fledglings of better body condition nor did they produce more or better fledglings than newly formed pairs consisting of at least 1 experienced breeder, that is, individuals that had bred before. Individuals produced fewer fledglings when they were paired with an inexperienced breeder, especially when females were paired with inexperienced males. Although clutch size was not affected by mate retention or breeding experience, pairs consisting of inexperienced breeder(s) had a relatively higher predation rate of eggs and/or nestlings because they may be less effective in nest defense. The onset of breeding was advanced in the year following mate retention, but not in the second year thereafter, when pairs still remained together. Furthermore, only the breeding experience of the male determined the onset of breeding: Pairs consisting of inexperienced males bred later in the season. Our results suggest that breeding experience, and particularly the breeding experience of the male, but not mate retention, is important in determining the breeding performance of hair-crested drongos.

Description: The astonishing diversity of floral form in angiosperm plants is driven in large part by preferences of pollinators for various floral traits, including learned preferences. Remarkably, almost all of a vast literature on learning and memory in pollinators relates to nectar as a reward, even though bees and many flies, beetles, and butterflies must collect pollen. In this study, we asked if bees formed preferences for plant species from which pollen had been collected successfully. Using absolute conditioning, we gave pollen foraging bees experience with plant species that offered only pollen rewards. Naive bees generally showed modest preferences, whereas experienced bees adopted strong preferences for those species over alternative species not previously experienced. Learned preferences were retained for at least 24h, consistent with preferences learned with nectar rewards. These experience-mediated changes in preference raised the possibility that bees formed associations between particular floral features and pollen rewards. We therefore asked if learned preferences required that bees successfully collect pollen. Using differential conditioning, we determined that learned preferences were strongly influenced by receipt of a pollen reward. In a final experiment, we characterized the importance of 2 floral features, the corolla and the anther, in the expression of learned preferences. Although experience altered responses to both floral parts, responses to anthers were influenced more strongly. We discuss recent evidence in the literature for associative learning with pollen rewards and propose that learned preferences in the context of pollen collection have played an important role in floral display evolution.

Description: The jumping spider genus Myrmarachne (Salticidae) consists of over 200 species of morphologically accurate ant mimics, enabling Myrmarachne to evade ant-averse predators that confuse the spiders with ants (Batesian mimicry). A conspicuous but untested trait of Myrmarachne , which is frequently mentioned in the literature, is locomotory mimicry. For these spiders, locomotion that is more ant like than salticid like may be an integral part of the suite of mimetic signals. We quantified the locomotory pattern of several species of non-ant-like salticids, Myrmarachne , and ants from Australia. We found that the locomotion of the mimics generally resembles that of ants, but not of other salticids. To tease out the effects of locomotion from those based on morphology, ant-eating salticids as visual predators were presented with 3D animations of ant-like salticids walking either in ant or in salticid fashion. Ant-eating salticids spent significantly longer looking at the stimulus with ant-like movement and were significantly more likely to visually track and stalk the stimulus with ant-like movement. Overall, our results suggest that there is selection pressure on Myrmarachne for increased resemblance to a model by locomotor mimicry, despite the associated costs when faced with ant-eating predators.

Description: The sensory trap model of signal evolution hypothesizes that signalers adapt to exploit a cue used by the receiver in another context. Although exploitation of receiver biases can result in conflict between the sexes, deceptive signaling systems that are mutually beneficial drive the evolution of stable communication systems. However, female responses in the nonsexual and sexual contexts may become uncoupled if costs are associated with exhibiting a similar response to a trait in both contexts. Male sea lamprey ( Petromyzon marinus ) signal with a mating pheromone, 3-keto petromyzonol sulfate (3kPZS), which may be a match to a juvenile cue used by females during migration. Upstream movement of migratory lampreys is partially guided by 3kPZS, but females only move toward 3kPZS with proximal accuracy during spawning. Here, we use in-stream behavioral assays paired with gonad histology to document the transition of female preference for juvenile- and male-released 3kPZS that coincides with the functional shift of 3kPZS as a migratory cue to a mating pheromone. Females became increasingly biased toward the source of synthesized 3kPZS as their maturation progressed into the reproductive phase, at which point, a preference for juvenile odor (also containing 3kPZS naturally) ceased to exist. Uncoupling of female responses during migration and spawning makes the 3kPZS communication system a reliable means of synchronizing mate search. The present study offers a rare example of a transition in female responses to a chemical cue between nonsexual and sexual contexts, provides insights into the origins of stable communication signaling systems.

Description: Weather is a crucial factor affecting the onset and end of breeding in birds. However, a few studies have clearly indicated that other factors—breeding parameters and/or individual traits—can also exert an influence. Our study aimed to determine how breeding experience and parental investment are related to the start and the end of the breeding season. We used age and pair-bond duration as predictors of breeding experience. We presumed, firstly, that older birds with a longer pair-bond duration would start breeding earlier, and secondly, that greater parental investment (expressed as breeding success in the previous season) favored later breeding. We tested the above hypotheses on an urban population of blackbirds ( Turdus merula ) in 2 parks in the city of Szczecin (western Poland) over 19 years. Despite the importance of weather variables, breeding experience expressed as age and pair-bond was shown to be a significant factor, too. Older birds with more bond experience started breeding sooner. Toward the end of the breeding season older, more experienced birds prolonged this period. We also observed senescence, which was manifested as the shortening of the breeding season. Those birds with more success in the previous season prolonged their breeding period in the following season; this contradicted our hypothesis. Temperature and precipitation were negatively related to the initiation date of the first clutch but positively to the initiation date of the last one. Our survey clearly showed the importance of breeding experience with the same partner and underlined the advantages of monogamy.

Description: Host-plant shifts have significantly contributed to the diversification of phytophagous insects. The contact sex pheromones of such insects may be modified by the plant they feed on, thereby contributing to the formation/maintenance of sister species on different plants. Here, we addressed this issue using 2 sister species of specialist phytophagous flea beetles Altica fragaria and Altica viridicyanea , and their oligophagous F 1 hybrids. Specifically, we tested 1) if males from these Altica species recognize conspecific females based on their cuticular hydrocarbon (CHC) profile, 2) if the host plant affects the CHC profile of hybrid females, and 3) whether hybrid males distinguish between hybrid females raised on different host plants. Mate choice tests revealed that males use CHCs to identify conspecific mates. We then identified different CHC profiles in females of the 2 species and showed that the profile of CHCs in hybrids is modified by the host plant in which the beetles develop. Finally, we found that hybrid males raised on one host plant choose females with a matching profile, but this is not the case for males raised on the other plant. Our results suggest that plasticity in the expression of CHCs may have contributed to the original speciation process between the parental species. This reinforces the key role of host plants in shaping the evolution of reproductive isolation among herbivore populations.

Description: How animals trade-off food availability and predation threats is a strong determinant of animal activity and behavior; however, the majority of work on this topic has been on individual animals, despite the modulating effect the presence of conspecifics can have on both foraging and predation risk. Although these environmental factors (food and predation threat) vary spatially within habitats, they also vary temporally, and in marine habitats, this can be determined by not only the diel cycle but also the tidal cycle. Humbug damselfish, Dascyllus aruanus , live in small groups of unrelated individuals within and around branching coral heads, which they collectively withdraw into to escape a predation threat. In this study, we measured the proportion of individuals in the colony that were outside the coral head before and after they were scared by a fright stimulus and compared the responses at high tide (HT) and low tide (LT). We found that a greater proportion of the shoal emerged after the fright stimulus at HT and in larger groups than at LT or in smaller groups. We also quantified the pattern of emergence over time and discovered the rate of emergence was faster in larger shoals as time progressed. We show that shoals of fish change their behavioral response to a predation threat in accordance with the tide, exemplifying how temporally variable environmental factors can shape group movement decisions.

Description: The growing body of literature on social behavior in fruit flies opens up exciting opportunities for addressing an unresolved issue involving the degree of correlation between behavioral traits in larvae and adults. Although the prevailing adaptive decoupling hypothesis states that metamorphosis is associated with the disruption of genetic correlations between juvenile and adult traits, 2 alternative hypotheses are that, sometimes, a positive correlation may be adaptive, and that, often, the underlying genetic architecture will prevent perfect decoupling. We used lines of the Drosophila Genetic Reference Panel to quantify the degree of sociality in larval and adult fruit flies and then examined the correlation between the life stages. To verify that our social behavior scores did not merely reflect variation in activity levels, we also quantified larval and adult activity. Although we found significant variation in social behavior and activity among larvae and adults, both traits were decoupled between larvae and adults. Social behavior and activity were not positively correlated within each life stage either. Although our results agree with the adaptive decoupling hypothesis, both ultimate and proximate considerations suggest that, generally, we should expect the degree of decoupling to vary between species and traits.

Description: Birds migrating between distant locations regularly perform long continuous flights lasting several days. What compass mechanism they use is still a mystery. Here, we use a novel approach, applying an individual-based model, taking compass mechanisms based on celestial and geomagnetic information and wind into account simultaneously, to investigate what compass mechanism likely is used during long continuous flights and how wind drift or compensation affects the resulting tracks. We found that for the 6 cases of long continuous migration flights, the magnetoclinic route could best explain the route selection in all except one case compared with the alternative compass mechanisms. A flight strategy correcting for wind drift resulted most often in routes ending up closest to the predicted destinations. In only half of the cases could a time-compensated sun compass explain the migration routes observed with sufficient precision. Migration from Europe to the Siberian tundra was especially challenging to explain by one compass mechanism alone, suggesting a more complex navigation strategy. Our results speak in favor of a magnetic compass based on the angle of inclination used by birds during continuous long-distance migration flights, but also a capacity to detect and correct for drift caused by winds along the route.

Description: Sexual cannibalism is an extreme expression of sexual conflict, which can grant females significant fitness benefits, particularly if female fecundity depends on foraging success. However, when cannibalism is precopulatory, there is the risk that females remain unmated. Therefore, males simultaneously present the option of a meal or a mate to the females they encounter. The springbok mantis ( Miomantis caffra ) is highly aggressive, and when females cannibalize males, it is exclusively precopulatory. However, females can circumvent the risk of infertility by reproducing asexually, providing a rare opportunity to explore the interaction between sexual cannibalism and facultative parthenogenesis. We kept female mantises on high and low feeding regimes, and paired them with males, to examine how body condition and age influenced rates of cannibalism. We also investigated whether reproductive mode (sexual or asexual) influenced fecundity by measuring ootheca weight. Overall, there was an extremely high average cannibalism frequency (~62%), but no significant difference in frequencies of cannibalism between feeding regimes. Although there was a relationship between female condition and fecundity, influenced by feeding treatment, the mode of reproduction (sexual or asexual) did not result in any difference in ootheca weight. Using information-theoretic approaches, we determined that, of the variables examined, female age best accounted for cannibalistic behavior and that females became less aggressive and more likely to mate over time. This suggests that, although parthenogenesis may allow females to cannibalize males at a high frequency without incurring the cost of infertility, they may still benefit from reproducing sexually later in their lives.

Description: Learning is a fundamental biological adaptation that is widespread throughout the animal kingdom. According to previous research, 2 conditions are necessary for learning to be adaptive: between-generation environmental variability and within-generation environmental predictability. In this article, we show that between-generation variability is not necessary and that instrumental learning can provide a selective advantage in a complex environment, where an individual is exposed to a large number of different challenges during its lifespan. We construct an evolutionary model where individuals have a memory with limited storage capacity, and an evolving trait determines the fraction of that memory that should be allocated to innate responses to the environment versus learning these responses. The evolutionarily stable level of learning depends critically on the features of the environmental process, but generally increases with environmental complexity. We conclude by emphasizing that the specific advantages of learning should be distinguished from the general advantages of phenotypic plasticity, and we discuss possible routes to empirically test our claims.

Description: Expression of sexually selected signals in many species varies over time of day and season. A key model system to study this variation in signal expression is birdsong. Yet, despite good ecological understanding of why song varies across time of day and season, much of the individual variation remains unexplained. Although some of the interindividual variation in singing depends on the quality or motivation of an individual, it can also vary with other characteristics. Because singing has been shown to vary with personality traits in specific contexts, personality is thus an important candidate to explain part of the variation in seasonal and daily singing. Using a personality-typed field population of great tits ( Parus major ), we here show that singing activity peaked at dawn during the fertile period of the females and that the association between male personality and singing activity depended on the reproductive stage of his mate; faster explorers significantly increased in singing activity during main periods of fertility and maternal investment (egg laying and incubation). Moreover, males with higher singing activity tended to raise more fledglings. Increased singing by faster explorers during key periods of female reproductive investment suggests that faster explorers are more responsive to changes in female reproductive stage, contrasting the general view that faster explorers are less responsive to environmental and social changes. Most importantly, these findings highlight that multiple factors including personality need to be integrated when assessing causes of variation of highly variable sexually selected signal traits.

Description: Eavesdropping predators and parasites that exploit the mating signals of their prey often prefer to approach certain signal variants. However, victim finding depends on many different factors. Therefore, preferences of eavesdroppers may not always directly reflect the predation or parasitism risk of the signaler. Frog-biting midges ( Corethrella spp.) and their anuran hosts offer an excellent model system to investigate this correlation. Female Corethrella are vectors of trypanosomes in frogs and use the mating calls of their anuran hosts to localize them. We tested whether the acoustic preferences of Corethrella reflects the parasitism risk of male frogs by Corethrella and trypanosomes in the field. We conducted acoustic attraction and preference tests with Corethrella in the field and used the results of the preference tests to estimate a linear model (LM) and predict the parasitism risk of sympatric frog species by Corethrella . Our preference tests in the field showed that frog-biting midges preferred higher call rates, longer calls, a frequency around 2kHz, and sounds that were broadcast near the ground. Anuran species that were predicted by our LM to produce the most attractive signal showed the highest rates of parasitism by frog-biting midges and trypanosomes. Thus, acoustic preferences of eavesdropping Corethrella can be used to predict not only the parasitism rate of their host species by Corethrella but also the risk of subsequent trypanosome transmission.

Description: Animals in social groups can acquire information about the need for antipredator behavior by personally sampling the environment or from information provided by others. Use of such social information is expected to be adjusted according to its reliability, but experimental tests are rare and tend to focus just on alarm calls. We use detailed behavioral observations, acoustic analyses, and playback experiments to investigate how differences in sentinel dominance status affect the behavioral decisions of foraging dwarf mongooses ( Helogale parvula ). Dominant individuals acted as sentinels considerably more often than subordinate group members and used higher sentinel posts for guarding, making them potentially higher-quality sentinels in terms of experience and optimal positioning for predator detection. Surveillance calls produced during sentinel bouts contained vocal information about dominance status. Playback experiments showed that foragers used surveillance calls to detect sentinel presence and identity, and adjusted their vigilance behavior accordingly. When a dominant sentinel was on duty, compared with a subordinate groupmate, foragers increased reliance on social information, gathered less information through personal vigilance, and focused more on foraging. Our study contributes novel evidence that a major benefit of individual- and class-specific vocalizations is the potential to assess differences in caller information quality.

Description: The mechanisms that determine the evolutionary adaptations of scavengers to carrion exploitation have been well established. In contrast, little is known about coexistence during carrion exploitation based on behavioral traits and considering obligate and facultative species together. This study revisits the hypotheses of behavioral organization within the guild of necrophagous birds in light of the adaptive processes of specialization to carrion exploitation. We used a detailed dataset of observations from high-quality video recordings in the 2 regions with the most diverse and abundant populations of European avian scavengers. Active feeding time varied between species, with the obligate scavengers spending more time eating. The way that scavengers ate the food (i.e., on the ground or carrying away) diverged among species, with species with longer and more pointed beaks and a greater prehensile ability (of talons to grip things) carrying the remains away more often. We recognized the diversity and complementarity of strategies aimed at exploiting the same resource by different species and age classes. Scavenger species were clustered according to the relationship between the time active at the feeding site and the number of feeding pecks, leading to a decrease in competition for resource exploitation, as well as an occupation of specialized trophic niches. The study of active-consumption rates showed that eagles and vultures obtained most and a half, respectively, of their daily energetic requirements from each feeding event, reinforcing the important role of this relevant food source from ecological, evolutionary, behavioral, and conservation standpoints.

Description: In most cooperative breeders, helping is directed at close kin, allowing helpers to gain indirect fitness benefits by increasing the reproductive success of close relatives, usually their parents. Extrapair paternity (EPP) occurs at high rates in some cooperative breeders, reducing the relatedness of helpers to the young they help raise. Even so, a son that helps is related to the brood by at least 0.25 through his mother and to within-pair young by 0.5, whereas a potential helper that has EPP in his own nest is related only to the offspring he sires and unrelated to any extrapair offspring. In birds, EPP often favors older males, which in the extreme case can result in sons being more closely related to young in their parents’ nest than to young in their own nests. The fitness benefit of helping will thus be enhanced if helping lightens the workload and increases survival of helpers and their fathers, enabling them to become old, hyper-successful extrapair sires. Here, we develop and analyze a proof-of-concept model, grounded in the western bluebird ( Sialia mexicana ) system, demonstrating the conditions under which high population levels of EPP can generate inclusive fitness benefits of helping behavior that outweigh the costs. This model provides a new perspective on the relationship between EPP and helping behavior in cooperative breeders and suggests a strong need for empirical work to gather unprecedented data on paternity over the lifetime of helpers and their parents.

Description: Animals can be flexible in their migration strategies, using several wintering sites or a variety of routes. The mechanisms promoting the development of these migratory patterns and their potential fitness consequences are poorly understood. Here, we address these questions by tracking the dispersive migration of a pelagic seabird, the Atlantic puffin Fratercula arctica , using over 100 complete migration tracks collected over 7 years, including repeated tracks of individuals for up to 6 consecutive years. Because puffins have high flight costs, dispersion may generate important variation in costs of migration. We investigate differences in activity budgets and energy expenditure between different strategies. We find that puffins visit a range of overwintering destinations, resulting in a diversity of migratory routes differing in energy expenditures; however, they show interindividual similarity in the timings and location of major movements. We consider 3 hypothetical mechanisms that could generate this pattern: 1) random dispersion; 2) sex segregation; and 3) intraspecific competition or differences in individual quality. First, we dismiss random dispersion because individuals show strong route fidelity between years. Second, we find that sex differences contribute to, but do not account fully for, the migratory variation observed. Third, we find significant differences in breeding success between overwintering destinations, which, together with differences in foraging levels between routes, suggest that birds of different quality may visit different destinations. Taken together, our results show that dispersive migration is a complex phenomenon that can be driven by multiple factors simultaneously and can shape a population’s fitness landscape.

Description: Predation risk of individuals moving in multispecies herds may be lower due to the heightened ability of the different species to detect predators (i.e., mixed-species effect). The giraffe is the tallest land mammal, maintains high vigilance levels, and has good eyesight. As a result, heterospecific herd members could reduce their predation risk if they keyed off the giraffe’s antipredator behaviors. However, because giraffe rarely use audible alarm snorts, heterospecifics would need to eavesdrop on cues given off by the giraffe that indicate predator presence (e.g., body posture), to benefit from herding with giraffe. To test this, we compared the vigilance of zebra herding with conspecifics, with those herding with giraffe. Our results indicate that giraffe reduce zebra vigilance in zebra–giraffe herds and that in these herds, giraffe are the primary source of information regarding predation risk. In contrast, when zebra herd with conspecifics, they rely primarily on personal information gleaned from their environment, as opposed to obtaining information from conspecifics about predation risk.

Description: There is a growing evidence that members of animal groups synchronize their vigilance behavior to minimize predation risk. Because synchronized vigilance deviates from the classical vigilance models, which assume independent scanning, it is important to understand when and why it occurs. We explored vigilance behavior of wild boar ( Sus scrofa ) in a population subject to spatial variation in human hunting risk and seasonal variation in food availability. Group members synchronized their vigilance behavior. We hypothesized that vigilance synchronization would be context dependent and the trade-off between energy gain and safety would shape the relationship between the degree of vigilance synchronization and group size. We predicted weaker synchronization in large groups under heavy predation risk, due to benefits of numerical dilution, and stronger synchronization in large groups when food is limiting, due to intense food competition. The degree of synchronization decreased with increasing group size in the area where human hunting added another risk factor to the natural predation, pointing at the safety benefits of vigilance synchrony for members of small groups and the role of human-induced risk in shaping vigilance synchrony. We found no relation between vigilance synchrony and group size in a food scarce, winter season. However, low levels of vigilance and its synchronization observed in winter indicated that energy gain was prioritized over safety. Thus, members of wild boar groups can adjust levels of vigilance and its synchronization depending on the forage-risk trade-off set by the ecological context.

Description: When animals live near family members, this creates potential for incest and inbreeding depression, especially with unfamiliar kin. We examined incest avoidance when birds paired in kin groups and after dispersal in western bluebirds, Sialia mexicana , a cooperative breeder with a persistent, but low frequency of adult males helping at the nest. During their first winter, sons usually live in family groups comprised of parents, brothers, immigrant females, and more rarely, immigrant males and philopatric sisters. Sons usually pair with females that have joined their winter group, although some pair with females they encounter after dispersal. Incestuous pairing among relatives with relatedness ≥0.25 rarely occurred in either context, even considering extrapair fertilizations and other sources of unfamiliar kin. Sons pairing in their winter groups preferentially mated with immigrant females and actively avoided pairing with relatives. After dispersal into kin neighborhoods in spring, active incest avoidance was still required to explain low levels of incest with females within 600 m (2–3 territories) of where sons first bred, whereas absence of incest over larger distances could be explained by random mating. The probability of encountering a female relative within 600 m of where a male settled declined rapidly with dispersal distance to near zero for males dispersing 2 km from home. Although recognition is required to avoid incest when pairing in winter groups or settling near home, female-biased dispersal reduces likelihood of incest to near zero, even when males disperse relatively short distances (e.g., 2 km) from where they were born.

Description: According to the good-genes hypothesis, females prefer males with costly displays because the costs are reliable indicators of genetic quality. In leks, mating costs result from a multiplicative interaction between the number of display performances (lek attendance) and the energetic expenditure associated with each display performance. If males differ in their allocation strategies between the 2 components of mating effort, the reliability of display performance as an indicator of genetic quality may be disrupted. Here, we investigate the association between male genetic quality and both lek attendance and display performance in the Italian treefrog, Hyla intermedia . We recorded lek attendance and display performance (nightly calling effort) during 2 breeding seasons, and we set up a breeding experiment to evaluate sire effects on 3 larval fitness-related traits (growth rate, age, and size at metamorphosis). Attendance and calling effort were positively correlated with each other and both with male mating success, providing no evidence for a performance-attendance trade-off at the population level. In the breeding experiment, we found some evidence for an effect of sire identity and attendance on growth rate and age at metamorphosis, but no evidence for an effect of sire calling effort. We conclude that female preference, by imposing high-quality standards for calling males, strengthens the role of endurance rivalry in male mating competition, indirectly favoring males of higher-than-average mating effort. Under this scenario, although male displays are unreliable indicators of mating quality, females nevertheless gain benefits because of the reduced risk of coming on low-quality males.

Description: Fighting ability is generally assumed to predict male reproductive success; yet the mechanisms responsible for this relationship are seldom known. Competitively superior males may monopolize access to females, be preferred by females, invest more into courtship, or employ more coercive mating tactics. Differentiating these alternatives is essential to understand the interaction between male–male competition and female mate choice, and their influence on the evolution of male traits such as aggression. We tested whether male fighting ability, body size, courtship, or coercive behavior in intersexual interactions predict copulation success in the Australian Lake Eyre dragon lizard, Ctenophorus maculosus . Males with superior fighting ability had higher mating success; however, male harassment (biting and chasing) was a much stronger predictor of copulation, likely because aggressive males are able to overcome female resistance. Better fighters also copulated for longer, which may increase sperm transfer and/or fertilization success. Conversely, courtship effort (head-bobs) decreased copulation success, but only for small males. Females were no less likely to reject males with higher fighting ability, suggesting that females do not prefer these males. Furthermore, males with superior fighting ability were no more or less likely to court or harass females. Instead, both fighting ability and aggression towards females independently increased mating success, potentially generating mutually reinforcing selection on male aggression.

Description: In collective decision making, groups collate social information to inform their decisions. Indeed, societies can gather more information than individuals—so social information can be more reliable than private information. Colonies of Temnothorax albipennis can estimate the average quality of fluctuating nest sites when the sharing of social information through recruitment is rare. However, collective decisions in T. albipennis are often reached with the use of recruitment. We use a new experimental setup to test how colonies react to fluctuating nest sites when they use recruitment to reach a decision. When recruitment is used, colonies consistently choose nest sites that fluctuate between being "good" and "poor" over constantly "mediocre" alternatives. Moreover, they do so even if the fluctuating option is only "good" for 25% of the time. The ants’ preference for fluctuating nest sites appears to be due to tandem running. Even if a nest site is only briefly "good," scouts that experience it when it is "good" are likely to perform tandem runs to it. However, a constantly "mediocre" nest site is unlikely to ever provoke tandem runs. Consequently, the fluctuating nest sites attracted more tandem runs, even when they were only "good" for a short time. This led to quorum attainment in fluctuating nest sites rather than in constant "mediocre" nest sites. The results of this experiment demonstrate how sharing of social information through recruitment can change the outcome of collective decisions.

Description: Differences in male and female phenotypes are often the results of sexual selection. Over the years, a vast number of studies investigated how and why the 2 sexes differ in their physical appearance, reaching the conclusion that peculiar visual traits, signals, or ornaments usually evolve under the pressure of sexual selection to mediate intrasexual competition and mate choice. In social contexts, however, males and females can hold different roles and social interactions may depend on the individual gender. The female-dominated hymenopteran societies represent a fascinating scenario to investigate recognition and communication among individuals of different genders outside a common sexual selection framework because sterile female workers typically do not mate and are not attracted to males. Here, we used laboratory bioassays (lure presentation experiments) to evaluate the ability of Polistes dominula workers to discriminate between individuals of the 2 genders, investigating the relevance of the chemical and visual cues potentially involved in such process. Our results showed that P. dominula workers are able to discriminate between the sexes and visual cues rather than chemical ones are responsible for such discrimination.

Description: Quantifying the interaction between dispersal, kinship, and genetic structure can provide insights into the factors that shape kin-structured mammal societies. Here, we first employ a combination of 8 years of capture–mark–recapture and molecular data to characterize the spatial and genetic relationships among female snow voles ( Chionomys nivalis ) in a population located in the Swiss Alps. Subsequently, we examine the individual-level consequences of kin structure in terms of fitness and mating patterns. Behavioral data, relatedness estimates, and spatial autocorrelation analyses indicate that females show strong philopatry, with spatially clustered females being characterized by high levels of genetic relatedness, leading to significant small-scale (〈30 m) spatial genetic structure (SGS). In line with selection favoring female philopatry, dispersing females had a lower fitness compared with philopatric individuals. However, we found a negative association between female reproductive success and the number of neighboring females. This suggests that female kin clustering does not constitute an adaptive strategy in this species, but rather that site tenacity is a by-product of the costs of dispersal. Although dispersal is frequently invoked as a means to avoid inbreeding, our results provide no evidence for premating inbreeding avoidance, which is in line with previous studies on mammals. Instead, in the majority of years, we observed that pairs were more-closely related than expected by chance. However, we found that both males and females with related partners had reduced reproductive success, suggesting the existence of inbreeding depression and/or postmating inbreeding avoidance mechanisms. On the whole, our results show how quantification of SGS within populations can provide insights into individual dispersal behavior and its fitness consequences, and into the ways in which social and genetic structure interacts to shape the evolution of free-living populations.

Description: The so-called "strength of weak ties" is a central concept in social network theory, especially for understanding how information and diseases are transmitted through socially structured populations. In general, weak ties occur in networks where relatively few individuals are responsible for maintaining linkages between groups of individuals that would otherwise be poorly connected. This common structural motif can be seen in the social networks of species with fission–fusion social organization, such as giraffe ( Giraffa camelopardalis ). Giraffe social networks are characterized by social cliques in which individuals associate more with members of their own social clique than with those outside their clique. Individuals involved in weak, between-clique social interactions are hypothesized to serve as bridges by which an infection may enter a clique and, hence, may experience higher infection risk. Here, we address this and other hypotheses explaining helminth infection patterns in wild giraffe, exploring the relative roles of the social network and ranging behavior in determining infection risk. We show that infection risk is more influenced by weak ties with individuals outside one’s clique than by repeated contact with a core set of associates. Even when controlling for age and home range size, individuals who engaged in more between-clique associations, that is, those with multiple weak ties, were more likely to be infected with gastrointestinal helminth parasites. Our results suggest that diverse social interactions with giraffe from multiple cliques may increase exposure to pathogens. The importance of weak ties in pathogen transmission has only rarely been empirically demonstrated in wildlife.

Description: Remote sensors such as Doppler radars are providing novel insights into the migrations of diverse animal taxa, but limits in scope and sensitivity can hamper the utility of these tools. For example, studies investigating whether songbirds compensate effectively for wind displacement during nocturnal migration have been challenged by the need to assess behavior on a large scale. In addition, these studies typically overlook the potential role low-altitude diurnal flights play in dealing with unfavorable winds. In such cases, a combination of approaches—new and traditional—may be necessary to understand behavior more completely. Here, we unite ground-based visual observations with a new radar analysis method to investigate how songbirds deal with crosswinds over the northeast United States. We find that nocturnally migrating birds experienced significant wind drift, even though they often flew at 90° or more to the wind direction. Significantly, more birds undertook reoriented diurnal flights after nocturnal wind drift, and wind influence, nocturnal migration intensity, and time of season together explained the majority of variation in counts of these "morning flights." This study shows that bird behavior during migration can be strongly shaped by the danger of wind drift and that some songbird species respond to drift with reoriented diurnal migratory flights. Knowledge of birds’ interactions with wind is essential for successfully modeling migratory behavior and assessing the risks associated with changing habitats and meteorological patterns. Furthermore, an understanding of the degree to which drift defines migratory behaviors may have value across animal taxa.

Description: The question, "Why should prey advertise their presence to predators using warning coloration?" has been asked for over 150 years. It is now widely acknowledged that defended prey use conspicuous or distinctive colors to advertise their toxicity to would-be predators: a defensive strategy known as aposematism. One of the main approaches to understanding the ecology and evolution of aposematism and mimicry (where species share the same color pattern) has been to study how naive predators learn to associate prey’s visual signals with the noxious effects of their toxins. However, learning to associate a warning signal with a defense is only one aspect of what predators need to do to enable them to make adaptive foraging decisions when faced with aposematic prey and their mimics. The aim of our review is to promote the view that predators do not simply learn to avoid aposematic prey, but rather make adaptive decisions about both when to gather information about defended prey and when to include them in their diets. In doing so, we reveal what surprisingly little we know about what predators learn about aposematic prey and how they use that information when foraging. We highlight how a better understanding of predator cognition could advance theoretical and empirical work in the field.

Description: Cooperative breeding occurs in several major animal phyla, predominantly in arthropods and chordates. A number of comparative analyses have focused on understanding the evolution of cooperative breeding, yielding mixed, inconclusive, and often phyla-specific findings. We argue that much of this ambiguity results from an erroneous classification of social systems into noncooperatively and cooperatively breeding species. The shortcomings of this assumption are apparent among birds where noncooperative species constitute a heterogeneous group: some species are clearly non–family living, with offspring dispersing at or shortly after nutritional independency, whereas other species form persistent family groups through offspring delaying their dispersal substantially beyond independency. Here, we propose an objective, life history–based criterion classifying noncooperative bird species into non–family living and family living species. We demonstrate that by using the family time (the time offspring remain with its parent/s beyond independence) and body size–scaled reproductive investment, we are able to differentiate 2 groups with contrasting life histories. Our classification matches seasonal environmental variation experienced by different species: family living species postpone dispersal beyond the onset of less favorable autumn conditions. We discuss the consequences of this new social system classification for evolutionary and ecological research, potentially allowing solutions to some of the most intriguing riddles in the evolutionary history of birds—and cooperative behavior itself.

Description: Humans have brought about unprecedented changes to environments worldwide. For many species, behavioral adjustments represent the first response to altered conditions. In this review, we consider the pivotal role that behavior plays in determining the fate of species under human-induced environmental change and highlight key research priorities. In particular, we discuss the importance of behavioral plasticity and whether adaptive plastic responses are sufficient in keeping pace with changing conditions. We then examine the interplay between individual behavioral responses and population processes and consider the many ways in which changes in behavior can affect ecosystem function and stability. Lastly, we turn to the evolutionary consequences of anthropogenic change and consider the impact of altered behaviors on the evolutionary process and whether behavior can facilitate or hinder adaptation to environmental change.

Description: Non-native species can serve as a prey resource for native predators. Yet because there is often no shared evolutionary history between the predator and prey, individuals within a predator population may vary greatly in their willingness to consume a recently introduced, yet profitable prey. Here, we measured individual variation in diet, behavior, and demographic traits of the native predatory mud crab, Panopeus herbstii , and evaluated how these traits influenced an individual’s consumption of a recently introduced, non-native crab, Petrolisthes armatus , using both simultaneous and no-choice assays. These same individual predatory mud crabs were also assayed to quantify their antipredator reaction and exploratory behavior. Results indicated significant variation in the diets of individual predators with 45% specializing on native mussels, 14% specializing on non-native Petrolisthes , and the remainder eating multiple prey species. When given a choice of alternative prey, individual Panopeus predators that consumed a larger proportion of Petrolisthes were female, smaller, and more likely to flee in response to predators. When given no choice of alternative prey, Petrolisthes was consumed more frequently by Panopeus that were female and less exploratory. We suggest that individuals that more readily consume non-native Petrolisthes may be attempting to reduce competition with conspecifics that are larger, more aggressive, exploratory, and male. Our results suggest that at least initially following invasion, adoption of a non-native prey species into the diet of a native predator may not occur universally within the population. Such nonuniform predation pressure could contribute to the non-native prey’s release from natural enemies.

Description: In socially monogamous species, in which both sexes provide essential parental care, males as well as females are expected to be choosy. Whereas hundreds of studies have examined monogamy in biparental birds, only several such studies exist in fish. We examined mate choice in the biparental, colonial cichlid fish Neolamprologus caudopunctatus in Lake Tanganyika, Zambia. We genotyped more than 350 individuals at 11 microsatellite loci to investigate their mating system. We found no extrapair paternity, identifying this biparental fish as genetically monogamous. Breeders paired randomly according to their genetic similarity, suggesting a lack of selection against inbreeding avoidance. We further found that breeders paired assortatively by body size, a criterion of quality in fish, suggesting mutual mate choice. In a subsequent mate preference test in an aquarium setup, females showed a strong preference for male size by laying eggs near the larger of 2 males in 13 of 14 trials.

Description: Demographic variation, such as changes in population size, affects group-living conditions and thus creates new opportunities for individuals to interact socially. To understand how this variation in the social environment affects social structure, we used social network analysis to explore affiliative behaviors of nonpup (i.e., 1 year or older), female, yellow-bellied marmots ( Marmota flaviventris ). We examined 4 social attributes (outdegree, indegree, closeness centrality, and betweenness centrality) to measure social plasticity in response to group size variation. We found that, in response to increases in group size, individuals established fewer social connections than possible, which suggests that marmots experience constraints on sociality. Similarly, closeness and betweenness centrality decreased as group size increased, suggesting that females are expected to lose influence over other members of the group as group size increases, and there are substantial constraints on marmots transmitting information to others in large groups. Our results also suggest that group-level responses, such as behavioral plasticity, can be explained by individual-level mechanisms that evaluate the costs and benefits of sociality. Interestingly, the mechanistic basis of these group-level responses may, at times, follow patterns expected by chance. We propose that further research is necessary to uncover the mechanisms underlying the individual-level behavioral response. Like group size effects studied in other domains, formally considering group size effects on social structure may shed novel light on the constraints on sociality.

Description: Postcopulatory variation in reproductive success is fundamental for sexual selection. Because evolutionary change is impossible without a heritable basis for variation, the study of postcopulatory variation has mainly focused on genetic differences between males, that is, the effect of sperm competition or differential female responses toward male genotypes (cryptic female choice). The role of environmental components in shaping postcopulatory variation in reproductive success is well known, for example, in the form of damaging lifestyle effects on sperm, but their effect on eliciting female responses has rarely been tested, as has its relative significance compared with male genotypic effects. Here we provide such a test in bedbugs, a species where cryptic female choice has been hypothesized to be directed toward specific sperm genotypes. We measured female transcriptomic responses after experimentally controlling the male genetic and environmental component of the ejaculate. For identical female genetic background and identical male age at mating, we analyzed female gene expression in response to insemination with sperm of 3 different inbred populations (genotypes), each exposed to 1 of 2 environmental treatments (sperm storage duration in the male). Females responded mainly to environmental variation: 〉15 times more genes were differentially expressed, including stress response genes, compared with male genotypic variation. Our results suggest that postcopulatory natural selection exists and plays a significant role in the evolution and diversification of reproductive traits. Our results add complexity to testing the cryptic female choice hypothesis and show that nongenetic ejaculate effects are an important but underappreciated source of variation in biology.

Description: Heterospecific eavesdropping on alarm calls is well documented, but less is known about the factors influencing asymmetry in the reliability of heterospecific alarm calls. Partial overlap of predators between heterospecifics has been hypothesized as 1 possible mechanism driving asymmetric eavesdropping. We tested the responses of common mynas ( Acridotheres tristis ) and red-vented bulbuls ( Pycnonotus cafer ) to reciprocal playbacks of alarm and social calls by measuring changes from baseline in the rates of fly-bys near the speaker and in rates of singing. We found an asymmetric communication network between bulbuls and mynas: bulbuls only responded to conspecific alarm calls, whereas mynas responded to both bulbul and conspecific alarm calls. This communication asymmetry may be due to a partial overlap in predators between species. Mynas were observed to spend time in both trees and on the ground and may be susceptible to both aerial and ground predators. We observed bulbuls primarily in trees and therefore may be susceptible primarily to aerial predators. If this is the case, then the alarm calls of mynas are less reliable to bulbuls compared with the reliability of alarm calls of bulbuls to mynas. However, further studies into the predators of each species are necessary before drawing a definitive conclusion. Our study demonstrates a differential responsiveness of 1 species on the alarm calls from another species for predator information and underscores the importance in considering heterospecific communication networks in the removal of species from a community.

Description: Allonursing, the nursing of another female’s offspring, is assumed to impose a substantial energetic cost given the high cost of lactation to mothers. However, these costs have not been quantified. In cooperatively breeding mammals where helpers contribute to lactation, they might be expected to modify their behavior to mitigate these potential costs. Here, we show that overnight weight loss during lactation did not differ between allonurses and controls. However, meerkat helpers that allonursed do not gain weight over a reproductive bout as non-allonursing subordinate females did, suggesting that allonurses may incur some cost. Allonurses may mitigate the costs by increasing foraging effort during lactation. Allonurses do not, as expected, reduce investment in other cooperative behaviors during lactation. We suggest that the increase in cooperative behavior, including allonursing, may serve a social function, but further work is needed to confirm this hypothesis.

Description: The adrenocortical stress response may divert energy away from sexual ornamentation, such that ornaments signal exposure or resistance to physiological stress. Alternatively, steroid glucocorticoids released via the stress response may support ornament development by stimulating foraging and metabolism. The relationship between glucocorticoids and ornamentation may vary with ornament type and across age and sex classes that experience different resource allocation tradeoffs. In yellow warblers ( Setophaga petechia ), we conducted the first study to simultaneously assess whether relationships between corticosterone (the primary avian glucocorticoid) and ornamentation depend on sexual pigment type, age, and sex. We quantified carotenoid- and phaeomelanin-based pigmentation using spectrometry, and assayed corticosterone in feathers (CORT f ) to derive an integrative metric of corticosterone levels during molt. Yellow warblers with lower carotenoid hue (lambda R50) had higher CORT f , suggesting that carotenoid hue may signal stress during molt across age and sex classes. Carotenoid chroma also negatively correlated with CORT f . However, this correlation was absent in older males, seemingly because these males display more saturated carotenoid pigmentation, and thus less variance in carotenoid chroma. Young males with higher CORT f also tended to have poorer quality tertial feathers, indicating poor condition at molt. Phaeomelanin-based pigmentation was largely unrelated to CORT f , suggesting that pleiotropic effects do not link phaeomelanogenesis and CORT release. Finally, CORT f was repeatable across years within individuals. Thus, carotenoid- and phaeomelanin-based pigmentation communicate nonequivalent information about physiological stress, with carotenoid pigmentation having the potential to signal stable differences in stress levels that could affect fitness.

Description: Animal populations are currently under pressure from multiple factors that include human land use and climate change. They may compensate for such effects by reducing, either by habituation or by natural selection, the distance at which they flee from humans (i.e., flight initiation distance), and this adaptation may improve their population trends. We analyzed population trends of common breeding birds in relation to flight initiation distance and geographical location (latitude, longitude, and marginality of the breeding distribution) across European countries from Finland in the north to Spain in the south while also considering other potential predictors of trends like farmland habitat, migration, body size, and brain size. We found evidence of farmland, migratory, and smaller-sized species showing stronger population declines. In contrast, there was no significant effect of relative brain size on population trends. We did not find evidence for main effects of flight initiation distance and geographical location on trends after accounting for confounding and interactive effects; instead, flight initiation distance and location interacted to generate complex spatial patterns of population trends. Trends were more positive for fearful populations northward, westward, and (marginally) toward the center of distribution areas and more negative for fearless populations toward the south, east, and the margins of distribution ranges. These findings suggest that it is important to consider differences in population trends among countries, but also interaction effects among factors, because such interactions can enhance or compensate for negative effects of other factors on population trends.

Description: Sociality is associated with a variety of costs and benefits, one of which can be to increase the likelihood of individuals solving novel problems. Several hypotheses explaining why groups show higher innovative problem-solving efficiencies than individuals alone have been proposed including the sharing of antipredator vigilance and the pool-of-competence effect, whereby larger groups containing a more diverse range of individuals are more likely to contain individuals with the skills necessary to solve the particular problem at hand. Interference between group members may cause groups to have lower problem solving abilities, however. Using a simulation approach, we model the shape of the relationship between group-level problem-solving probability and group size across a range of facilitation and inhibition scenarios, various population distributions of problem solving, and a task requiring 1 action or 2 actions to be solved. Simulations showed that both sharing of antipredator vigilance and the addition of competent individuals to an existing group lead to positive relationships between group-level problem solving and group size that reach 100% solving probability, whereas interference effects generate group-solving probabilities that rise to a maximum and decrease again, generating a group size for which problem solving is maximized. In contrast, both inhibition and facilitation scenarios generate identical patterns of individual efficiencies. Our results have important implications for our ability to understand the mechanisms that underpin group-size effects on problem solving in nonhumans.

Description: Although personality has been well studied in a wide range of species, relatively few studies have assessed if behavior in standardized captive tests is predictive of behavior in the wild. We captured wild zebra finches around 2 breeding colonies and assayed their exploratory behavior with a novel environment test. The birds’ foraging behavior in the wild was also measured with the use of a passive integrated transponder tag system to monitor their use of feeders that were periodically moved around the colonies to assess exploratory behavior and sociality. During the same period, individuals’ reproductive success was monitored at the nest-boxes being used in this area. We found that our measures of sociality, wild, and captive exploration were repeatable, but contrary to our predictions, exploration in the novel environment test was not significantly correlated with exploration of feeders in the wild. We failed to find a predicted negative relationship between exploration and sociality, instead finding a significant positive correlation between exploration in the novel environment and sociality. Finally, we found little evidence that any of our measured personality traits influenced reproductive success at the colony, either individually or when the interactions between the personalities of both members of the pair were taken into account. The only exception was that highly exploratory males (assayed with wild feeder behavior) were more likely to make breeding attempts than less exploratory males. Our results suggest that researchers should use caution when using tests such as the classic novel environment test to make inferences about personality in wild populations.

Description: Life-history theory predicts a trade-off for allocation of limited resources to reproduction and self-maintenance; however, many of the underlying physiological mechanisms remain elusive. There is growing evidence for oxidative stress to play an essential role in this trade-off because some by-products from the immune system and from normal metabolism generate reactive oxygen species that can cause oxidative damage. We manipulated reproductive effort of male and female great tits shortly before reproduction by clipping feathers of either the male or female parent of pairs of known age, given that parental effort may differ between the sexes and change over the lifetime of an individual. We quantified the effect of the treatment on morphological, physiological, behavioral, and reproductive traits. We found that feather clipping led to a decrease in parental body mass and to a reduced clutch size. Nestlings raised by clipped fathers showed reduced body mass although feeding rate was equally high between clipped and control individuals. In contrast to our predictions, we found that the feather clipping did not affect oxidative status. However, independently of the treatment, adult males had higher antioxidant capacity than females and older males showed higher oxidative damage compared with yearlings. Thus, our results suggest that the self-maintenance was prioritized over reproduction. It suggests that males are more susceptible to increased workload than females and thus more likely to reduce allocation of resources to reproduction.

Description: In conspecific brood parasitism, some females ("parasites") lay eggs in nests of other females of the same species ("hosts"). This reproductive tactic is particularly common in waterfowl, in which studies suggest that parasites are often related to the host. Here, we test the hypothesis that hosts may discriminate and reject unrelated parasites. Based on observations and 〉4100h of digital video film, we analyze behavioral interactions at 65 nests of High Arctic common eiders during the laying sequence. We also estimate parasitism and host–parasite relatedness by albumen fingerprinting of 975 eggs from 232 nests. Among the video-filmed nests in which interactions were recorded during the egg-laying period, 11 had eggs from 2 females. At 8 of these 11 nests, there was overt female aggression and significantly lower host–parasite relatedness (mean coefficient of relationship r = –0.40) than in the nests with tolerant or no interactions ( r = 0.91). The results demonstrate active female kin discrimination in common eiders, used against nonrelatives that try to lay eggs in the nest. Other females trying to access the nest were often prevented from doing so: in 65% of 34 such attempts, the sitting female rejected the intruder. Brood "parasitism" in eiders and other waterfowl is complex, ranging from violent female conflict and parasitic exploitation of the host’s parental care to nest takeover and potential kin selection favoring acceptance of related parasites. These and other aspects of female sociality in eiders are discussed; in some respects, they may resemble certain long-lived matriarchal mammals.

Description: In social mammals, condition and health are important determinants of the ability of males to achieve high dominance rank. Measures of individual condition are also predicted to affect male fitness via female preference for high-quality mates. We examined intermale variation in phenotypic quality (immune function and oxidative stress) in relation to male dominance status and mating success in a species with prominent female choice and a lack of male–female sexual coercion, the rhesus macaque ( Macaca mulatta ). We quantified immunity via 2 functional assays of innate immune response (bacteria killing assay and hemolytic complement assay) and measured oxidative stress via a lipid peroxidation assay in 15 adult males from 1 social group of macaques on Cayo Santiago, Puerto Rico. We then observed these males throughout the mating season to test the prediction that males in better condition achieved higher mating success. Males with more robust innate immune response and lower oxidative damage mated with a greater number of potentially fertile females. Male dominance rank, however, also correlated with our measures of quality. Higher-ranking males had more robust functional innate immune response and lower levels of oxidative damage. After accounting for rank, male quality was no longer correlated with mating success. These results demonstrate a potentially important role of male phenotypic quality in the mating system of a long-lived, group-living primate. What are the exact behavioral mechanisms via which sexual selection may operate on traits related to immunocompetence and resistance to oxidative damage in this species, however, remains an open question.

Description: Pollinators have the capability of discriminating a wide variety of floral cues in order to identify rewarding flowers. However, little is known about how possible ecological or functional implications of horizontal and vertical positioning of flowers affect pollinator decision making. Flowers are commonly either arranged horizontally in meadows or vertically in inflorescences and blooming trees or bushes. Using bumblebees ( Bombus terrestris ), we here investigate if these 2 different foraging scenarios affect decision-making accuracy using an operant learning paradigm. Training foragers to feeders arranged either horizontally or vertically but bearing identical color or pattern cues, we found a highly significant and consistent difference in feeder choice accuracy. Bees presented with horizontally arranged feeders achieved accuracies of more than 90% by the end of the training. In contrast, bees foraging on vertically arranged feeders largely disregarded the feeder cues and accuracies remained well below 70%. Apart from feeder arrangement (horizontal, vertical) neither cue type (color, pattern), feeder display orientation (horizontal, vertical) nor vertical feeder distribution contributed significantly to choice accuracy. Training bees successively on vertical, horizontal, and vertical feeder arrays revealed that individual bees are capable of discriminating the presented feeder cues with high precision on the horizontal plane but did not use the acquired knowledge on subsequently presented vertically arranged feeders. Our results indicate that the spatial arrangement of flowers has marked effects on the foraging strategy employed by a generalist pollinator. We discuss the broader implications of foragers selectively allocating attention to focus on or disregard environmental information depending on spatial context.

Description: As for other pollinators, hummingbirds have been classified as trapliners, that is, foragers that repeat the order in which they will revisit several locations. Although the study of hummingbird foraging behavior is extensive, there has been no direct evidence for the repeatability of hummingbird traplines. Here, we show that male territorial rufous hummingbirds repeated the order in which they visited artificial flowers in an array, which we increased one by one from 2 to 5 flowers. Despite the large number of possible routes that the birds could have flown around the flower arrays, the birds flew only a very small subset of routes and those routes were most often the shortest distance routes around the flowers. To our knowledge, this is the first quantitative evidence that hummingbirds do develop traplines when foraging.

Description: Animals may perceive humans as a form of predatory threat, a disturbance, triggering behavioral changes together with the activation of physiological stress responses. These adaptive responses may allow individuals to cope with stressful stimuli, but a repeated or long-term exposure to disturbances may have detrimental individual- and population-level effects. We studied the effects of human activities, particularly hunting, on the behavior and physiological status of a near-threatened nongame steppe bird, the little bustard. Using a semiexperimental approach, we compared before, during, and after weekends: 1) the type and intensity of human activities and 2) the behavior and 3) physiological stress (fecal corticosterone metabolites) of wintering birds. Higher rates of human activity, in particular those related to hunting, occurred during weekends and caused indirect disturbance effects on birds. Little bustards spent more time vigilant and flying during weekends, and more time foraging in the mornings after weekend, possibly to compensate for increased energy expenditure during weekends. We also found increased physiological stress levels during weekends, as shown by higher fecal glucocorticoid metabolite concentrations. Increased corticosterone metabolite levels were associated with the highest levels of hunting-related disturbances. Little bustard showed marked behavioral and physiological (stress hormones) responses to human activities that peaked during weekends, in particular hunting. The long-term effect of this particular activity carried out during weekends from autumn throughout winter might adversely impact wintering populations of this nongame endangered species, potentially counteracting conservation efforts conducted on local as well as foreign breeding populations.

Description: Urbanization involves dramatic environmental alterations, which can limit survival and reproduction of organisms and contribute to loss of biodiversity. One such alteration is anthropogenic noise, which biases natural ambient noise spectra toward low frequencies where it may interfere with acoustic communication among birds. Because vocalizing at higher frequencies could prevent masking by noise, it has been hypothesized that species with higher song frequencies should be less affected by urbanization. Indeed, evidence is accumulating that urban birds often vocalize at higher frequency than nonurban birds. However, the extent to which singing frequency affects their success in cities is less clear. We tested this hypothesis with a comprehensive phylogenetic Bayesian analysis comparing song frequency of songbirds from 5 continents with 4 measures of success in urbanized environments. Tolerance to urbanization was not associated with dominant or minimum song frequencies, regardless of the metric used to quantify urban success and the intensity of the urban alterations. Although song frequency was related to habitat preferences and body size of the species, none of these factors explained the lack of association with urban success. Singing high may be beneficial for signal perception under noisy conditions, but these high frequencies are apparently no guarantee for the success of bird species in urbanized environments.

Description: Activity patterns have profound implications on primates’ morphology, physiology, and behavior and have likely driven their diversification. The last common ancestor of extant primates has been traditionally considered nocturnal although this notion has been recently debated due to emerging contradictory evidence. Previous studies underestimated the role of cathemerality (i.e., the ability to remain active throughout a 24-h cycle) by simplifying primate activity to the diurnal–nocturnal dichotomy. We estimated the evolutionary trajectories of activity patterns in primates and investigated how these may have influenced their diversification rates. We used a comprehensive data set to test multiple evolutionary hypotheses, following a robust Bayesian framework by using 5000 calibrated phylogenetic trees to account for phylogenetic uncertainty. Our results support a nocturnal ancestor that has shifted to diurnality in the Simiformes, has retained nocturnality in Lorisiformes and most Lemuriformes, and shifted to cathemerality in the ancestor of Lemuridae. The diversification of activity patterns in primates seems to have mainly arose by speciation rather than shifts between activity patterns, suggesting a low flexibility of diurnal and nocturnal patterns and the key importance of cathemeral activity as transitional state to shift between more specialized activity patterns. A cathemeral activity seems to appear well before diurnality in Malagasy lemurs, suggesting an ancient origin of this trait on the island and rejecting the hypothesis of a recent transition. The present research contributes to further disentangle the adaptive role of activity patterns in primate evolution.

Description: Many animals communicate through acoustic signaling, and "acoustic space" may be viewed as a limited resource that organisms compete for. If acoustic signals overlap, the information in them is masked, so there should be selection toward strategies that reduce signal overlap. The extent to which animals are able to partition acoustic space in acoustically diverse habitats such as tropical forests is poorly known. Here, we demonstrate that a single cicada species plays a major role in the frequency and timing of acoustic communication in a neotropical wet forest bird community. Using an automated acoustic monitor, we found that cicadas vary the timing of their signals throughout the day and that the frequency range and timing of bird vocalizations closely track these signals. Birds significantly avoid temporal overlap with cicadas by reducing and often shutting down vocalizations at the onset of cicada signals that utilize the same frequency range. When birds do vocalize at the same time as cicadas, the vocalizations primarily occur at nonoverlapping frequencies with cicada signals. Our results greatly improve our understanding of the community dynamics of acoustic signaling and reveal how patterns in biotic noise shape the frequency and timing of bird vocalizations in tropical forests.