ALBERT

Description: Quantifying drought at different temporal scales by varying the time length (i.e., grain) and timing (i.e., window) describes different hydrologic attributes which may uniquely influence animal food supplies, vegetation greenness/structure, and other factors affecting populations. For North American Great Plains breeding birds, drought had negative, but species and temporal scale‐dependent effects, supporting a larger pattern of multiple and nuanced wildlife responses to unfavorable weather. Considering drought at different temporal scales may better reveal mechanisms behind drought impacts on birds and other organisms, and improve understanding of the effects of anthropogenic climate change on species and the landscapes they inhabit. Abstract Global climate change is increasing the frequency and intensity of weather extremes, including severe droughts in many regions. Drought can impact organisms by inhibiting reproduction, reducing survival and abundance, and forcing range shifts. For birds, considering temporal scale by averaging drought‐related variables over different time lengths (i.e., temporal grains) captures different hydrologic attributes which may uniquely influence food supplies, vegetation greenness/structure, and other factors affecting populations. However, studies examining drought impacts on birds often assess a single temporal grain without considering that different species have different life histories that likely determine the temporal grain of their drought response. Furthermore, while drought is known to influence bird abundance and drive between‐year range shifts, less understood is whether it causes within‐range changes in species distributions. Our objectives were to (a) determine which temporal grain of drought (if any) is most related to bird presence/absence and whether this response is species specific; and (b) assess whether drought alters bird distributions by quantifying probability of local colonization and extinction as a function of drought intensity. We used North American Breeding Bird Survey data collected over 16 years, generalized linear mixed models, and dynamic occupancy models to meet these objectives. Different bird species responded to drought at different temporal grains, with most showing the strongest signal at annual or near‐annual grains. For all drought‐responsive species, increased drought intensity at any temporal grain always correlated with decreased occupancy. Additionally, colonization/extinction analyses indicated that one species, the dickcissel (Spiza americana), is more likely to colonize novel areas within the southern/core portion of its range during drought. Considering drought at different temporal grains, along with hydrologic attributes captured by each grain, may better reveal mechanisms behind drought impacts on birds and other organisms, and therefore improve understanding of how global climate change impacts species and the landscapes they inhabit.

Description: Landscape function is largely determined by landscape structure. Evidence suggests that landscape heterogeneity often benefits generalists over sympatric specialists. The scale at which animals perceive that heterogeneity likely varies across species and could play an important role in determining the species assemblages supported by different landscapes. In this study, we investigated the relative importance of landscape heterogeneity in the structuring of raptor assemblages in mixed-grass prairie. We compared niche breadth and overlap of 14 species in two landscapes that differed in heterogeneity. We used a modified line transect approach and distance sampling to determine approximate locations of raptors and mapped these locations in a GIS. We then compared land cover in buffered areas around detection locations to randomly selected locations at different scales. We calculated Outlying Mean Index to quantify niche breadth and compare among species. Species composition was similar in both landscapes, but niche characteristics differed according to heterogeneity. Raptor assemblages were better predicted by land cover composition in heterogeneous landscapes than by land cover configuration in homogenous landscapes. Outlying Mean Index analysis suggested that six of the 14 species occupied marginal niches and narrower niche breadths in homogeneous landscapes. None of these species demonstrated marginality but occupied broader niche breadths in heterogeneous landscapes. Our study provides evidence that heterogeneity is important in providing conditions necessary to support multiple, sympatric birds of prey in mixed-grass prairie. Species overlapped broadly under heterogeneity but less in landscapes with larger patches of distinct land cover types.

Description: [1]  The areal extent and volume of peak freshwater (river and lake) ice are quantified across the Northern Hemisphere for the period 1957-2002. Quantification is conducted using a degree-day ice-growth model and ice-growth coefficients defined for fourteen ice-specific hydro-climatic regions. The model is driven by ERA-40 gridded daily air-temperature data, and the Global Lakes and Wetlands Database is employed to spatially define rivers and lakes. Results indicate that the total area covered by freshwater ice, at peak thickness, north of the January 0 °C-isotherm (excluding the Greenland ice sheet) is 1.7x10 6 km 2 and the total freshwater-ice volume is 1.6x10 3 km 3 . This area is approximately equal to that of the Greenland ice sheet, and the volume to snow on land (Northern Hemisphere). Such values now permit a more complete quantification of the cryosphere (evaluations already having been completed for other components, such as snow, glaciers and sea ice) and provide a reference dataset for assessing future climate-related changes.

Description: Quantifying drought at different temporal scales by varying the time length (i.e., grain) and timing (i.e., window) describes different hydrologic attributes which may uniquely influence animal food supplies, vegetation greenness/structure, and other factors affecting populations. For North American Great Plains breeding birds, drought had negative, but species and temporal scale‐dependent effects, supporting a larger pattern of multiple and nuanced wildlife responses to unfavorable weather. Considering drought at different temporal scales may better reveal mechanisms behind drought impacts on birds and other organisms, and improve understanding of the effects of anthropogenic climate change on species and the landscapes they inhabit. Abstract Global climate change is increasing the frequency and intensity of weather extremes, including severe droughts in many regions. Drought can impact organisms by inhibiting reproduction, reducing survival and abundance, and forcing range shifts. For birds, considering temporal scale by averaging drought‐related variables over different time lengths (i.e., temporal grains) captures different hydrologic attributes which may uniquely influence food supplies, vegetation greenness/structure, and other factors affecting populations. However, studies examining drought impacts on birds often assess a single temporal grain without considering that different species have different life histories that likely determine the temporal grain of their drought response. Furthermore, while drought is known to influence bird abundance and drive between‐year range shifts, less understood is whether it causes within‐range changes in species distributions. Our objectives were to (a) determine which temporal grain of drought (if any) is most related to bird presence/absence and whether this response is species specific; and (b) assess whether drought alters bird distributions by quantifying probability of local colonization and extinction as a function of drought intensity. We used North American Breeding Bird Survey data collected over 16 years, generalized linear mixed models, and dynamic occupancy models to meet these objectives. Different bird species responded to drought at different temporal grains, with most showing the strongest signal at annual or near‐annual grains. For all drought‐responsive species, increased drought intensity at any temporal grain always correlated with decreased occupancy. Additionally, colonization/extinction analyses indicated that one species, the dickcissel (Spiza americana), is more likely to colonize novel areas within the southern/core portion of its range during drought. Considering drought at different temporal grains, along with hydrologic attributes captured by each grain, may better reveal mechanisms behind drought impacts on birds and other organisms, and therefore improve understanding of how global climate change impacts species and the landscapes they inhabit.