Data from: Evaluating biotic and abiotic drivers of avian community mobbing responses along urban gradients in Southern California

Urbanization is a significant pressure affecting wildlife, and has the
potential to greatly alter behavioral responses in animal communities. A
behavioral response that is potentially affected by urbanization is the
mobbing of predators by potential avian prey species. We explored the
effect of various abiotic and biotic factors in influencing avian mobbing
responses along an urban-rural gradient. We conducted predator simulations
by using playback of the vocalizations of the Western Screech-owl,
Megascops kennicottii, which is a predatory species that elicits a mobbing
response from other birds. These vocalizations, accompanied by stuffed
models of the screech-owls, were broadcast at a variety of points along an
urban-rural gradient in Los Angeles and Orange Counties in southern
California. We used an experimental approach using playback, i.e.,
vocalization and models, to investigate whether mobbing responses of birds
change in areas where predators may be naturally present (high vegetation
density) or absent (high impervious cover). We recorded the number of
individual birds and species that exhibited mobbing behavior at
experimental sites, as well as various biotic and abiotic factors that may
influence avian mobbing, including noise level, impervious surface cover,
avian community turnover across the urban-to-rural gradient, and the
structure of local vegetation, which we assumed may be important for
either hosting roosting screech-owls or providing cover for mobbing bird
species. For both the number of mobbing individuals and species, we showed
that mobbing responses decreased with increasing noise levels and
percentage of impervious surfaces and increased with increasing woody
vegetation. There was some evidence that predator presence influenced
mobbing responses. Our results show that the changes associated with
urbanization can significantly alter anti-predator behavior in birds, and
that these changes can alter avian social eavesdropping networks.

城市化是影响野生动物的重要压力源，且有可能极大改变动物群落的行为响应模式。潜在受城市化影响的一类行为响应，是鸟类潜在猎物物种对捕食者的围攻行为（mobbing behavior）。本研究探究了城乡梯度下各类非生物与生物因子对鸟类围攻行为的调控作用。我们通过回放西美鸣角鸮（Megascops kennicottii）的鸣叫声开展捕食者模拟实验，该物种为一种可诱发其他鸟类产生围攻行为的捕食者。我们将这些鸣叫声与西美鸣角鸮的剥制标本相结合，在南加州洛杉矶县与橙县的城乡梯度沿线多个点位进行了播放。本研究采用声音回放（playback，即鸣叫声播放与标本展示）的实验方法，旨在探究鸟类的围攻行为是否会在捕食者自然存在（植被密度较高）或缺失（不透水面覆盖度较高）的区域发生变化。我们记录了实验点位上表现出围攻行为的鸟类个体数量与物种数，同时记录了可能影响鸟类围攻行为的各类非生物与生物因子，包括噪音水平、不透水面覆盖度、城乡梯度下的鸟类群落更替情况，以及本地植被结构——我们推测其既可作为鸣角鸮的栖息场所，也能为参与围攻的鸟类提供庇护。无论是围攻鸟类的个体数还是物种数，我们的结果均显示：围攻行为随噪音水平与不透水面占比的升高而减弱，随木本植被覆盖率的提升而增强。另有部分证据表明，捕食者的存在与否会对围攻行为产生影响。本研究结果表明，与城市化相关的环境变化可显著改变鸟类的反捕食行为，且此类变化能够重塑鸟类的社会偷听网络（social eavesdropping networks）。