Wed, Aug 04, 2021:On Demand
Background/Question/Methods
Land cover changes that result from increasing urbanization alter habitat type, structure, and resource availability on local and global scales. Vultures provide important ecosystem services including disease management and nutrient cycling, making them an important feature of urban areas. For vultures, urbanization may have both positive and negative impacts, such as increased foraging opportunities due to the presence of roadkill and decreased nesting success due to human presence, complicating our understanding of the effect of urbanization on these essential species. I examined how local and landscape features affect roost attendance and nesting success of black vultures (Coragyps atratus) and turkey vultures (Cathartes aura) in the Charlotte Metropolitan Area, USA. I counted the number of vultures at twenty-nine permanent roost sites once a month between November 2019-March 2020 and November 2020-March 2021 and monitored the nesting activities and periods once a week between March and August 2020 at two rural black vulture nests and one urban black vulture nest. At each roosting site, I characterized vegetation height, roost height, right-of-way corridor width, and weather conditions, and measured land cover, carcass density, and Developed-Forest edge density in the surrounding landscape within radii ranging from 0.4km to 20km. I tested the effects of these variables on the number of vultures at roosts using generalized linear models and multi-model inference.
Results/Conclusions The best model for roost attendance included the date, wind speed, corridor edge vegetation height, carcass density within 15km and 20km of roosts, Developed land cover within 15km of roosts, and Developed-Forest edge density within 15km of roosts. Of these variables, Developed land cover was associated with higher numbers of vultures while all other variables were associated with lower roost attendance. The two rural black vulture nests each successfully fledged two young whereas the urban nest failed with no eggs hatched. The rural black vulture nests each had much less developed landcover and more forested landcover surrounding the site, potentially representing negative impacts of developed land cover on vulture nesting success. The negative effect of carcass density on vulture numbers suggests more reliance of vultures on trash and other anthropogenic food sources. The change in urban vulture diets may have important implications for urban systems, altering nutrient cycling within ecosystems and decreasing the reproductive success of urban vultures.
Results/Conclusions The best model for roost attendance included the date, wind speed, corridor edge vegetation height, carcass density within 15km and 20km of roosts, Developed land cover within 15km of roosts, and Developed-Forest edge density within 15km of roosts. Of these variables, Developed land cover was associated with higher numbers of vultures while all other variables were associated with lower roost attendance. The two rural black vulture nests each successfully fledged two young whereas the urban nest failed with no eggs hatched. The rural black vulture nests each had much less developed landcover and more forested landcover surrounding the site, potentially representing negative impacts of developed land cover on vulture nesting success. The negative effect of carcass density on vulture numbers suggests more reliance of vultures on trash and other anthropogenic food sources. The change in urban vulture diets may have important implications for urban systems, altering nutrient cycling within ecosystems and decreasing the reproductive success of urban vultures.