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

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.

有关城市化对鸟类影响的研究已探索了多样的行为模式（如觅食、繁殖、迁徙），但针对城市对鸟类集群习性影响的相关研究仍较为匮乏。诸多城市环境因子可能对集群鸟类产生影响，包括城市中不透水面（impervious surfaces）占比偏高、城市热岛效应，以及栖息地与资源（如食物、水源）可获得性的变化。
本研究依托五年期的公民科学数据平台eBird的公开数据，针对美国亚利桑那州凤凰城的崖燕（Petrochelidon pyrrhonota）——一种如今常于桥梁等临水或近水人工建筑上繁殖的常见集群鸟类——的集群规模开展城市影响相关调查。基于这类新热带迁徙鸟类在该沙漠环境中的独特繁殖习性，我们提出假设：凤凰城的崖燕会在食物与水源更充足、人工建筑更多的区域形成更大的集群。
研究结果显示，崖燕集群规模与距水源及农田的距离呈显著正相关，但与不透水面密度并无显著关联。上述结果表明，在该沙漠生态系统中，大量人类提供的食物与水源资源使得崖燕在繁殖季能够形成更大的社会集群。
尽管诸多研究证实了城市对本土野生动物的负面影响，但本研究结果凸显了城市与/或农业“绿洲”如何帮助部分本土物种摆脱自然资源胁迫，使其在受人类活动影响的环境中得以繁衍生息并扩大集群规模。