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Data from: Urban environmental predictors of group size in cliff swallows (Petrochelidon pyrrhonota): A test using community-science eBird data

McGraw, Kevin1; Rueda, Cassie2

Published Apr 23, 2025 on Dryad. https://doi.org/10.5061/dryad.c866t1gfd

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Abstract

Studies on the impacts of urbanization on birds have explored a wide variety of behaviors (e.g. foraging, breeding, migratory), but there is little research on the impacts of cities on avian coloniality. Various urban-environmental factors may impact colonial birds, including the predominance of impervious surfaces in cities, as well as the urban heat island effect and shifts in habitat and resource availability (e.g. food, water). Here we used five years of community-science data available in eBird to investigate urban impacts on group size in cliff swallow (Petrochelidon pyrrhonota), an abundant colonial bird species that now breeds readily under bridges and other built structures over or near water in Phoenix, Arizona, USA. We hypothesized that, based on the unique breeding habits of these neotropical migratory birds in this desert environment, swallows in Phoenix would form larger groups in areas with more food and water sources and with more built structures. In fact, we found that proximity to water sources and cropland, but not impervious surface density, was positively and significantly related to group size. These results suggest that, in this desert ecosystem, an abundance of often-human-provided food/water resources permits cliff swallows to form larger social groups during breeding. Although many studies show harmful impacts of cities on local wildlife, our findings highlight how urban and/or agricultural ‘oases’ may relieve some native species from natural resource stressors and permit them to thrive and increase in group size in human-impacted environments.