ALBERT

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: Many theoretical models on the evolution of nestling begging assume this behavior is costly, so that only nestlings in real need of food would profit from giving intensive signals to parents. However, evidence accumulated for the last 2 decades is either contradictory (growth costs) or scant (immunological cost). Here, we experimentally test the existence of both costs in pied flycatcher ( Ficedula hypoleuca ) nestlings, a species in which parents appropriately respond to honest begging signals. Nestlings were paired by nest of origin and similar body mass. In each pair, a nestling was forced to beg for 51s/meal, whereas the other begged for only 3.4s/meal, both receiving the same amount of food. Simultaneously, the nestling immune response to an antigen (phytohemagglutinin) was measured. Experimental nestlings showed reduced immunocompetence compared with control chicks, which in this species could be regarded as a genuine direct cost. High-begging nestlings also gained less mass during the daylight activity hours. However, they lost less mass while resting at night, resulting in similar mass gains for both groups across the whole daily cycle. This suggests that negative effects of excess begging on mass gain can be compensated for by nestlings, thus avoiding the negative fitness consequences (i.e., cost) of a retarded growth. Mixed results found in previous studies may reflect interspecific differences in compensatory changes in mass gain. But if such differences do not map into fitness consequences, they may be of little help to answer the question of whether begging entails direct growth costs.