Urban and rural chickadee response to novel object and simulated predator

Urbanization is changing natural landscapes worldwide, pushing species to quickly acclimate or adapt if they are to survive in urban environments. Mountain chickadees (Poecile gambeli) readily nest in both urban and rural environments without suffering apparent reproductive costs. However, whether urban-nesting chickadees are successful in these environments due to differences in behaviour between urban and rural birds remains untested. We examined the behavioural responses of urban and rural nesting mountain chickadee females when presented with a novel object (red plastic cup) or simulated predator (imitation squirrel model) at the nest. Behavioural responses depended on both the type of model and the habitat. As expected, mountain chickadees responded more strongly to squirrel models than novel objects; however, the magnitude of the difference in response depended on habitat. Urban birds seemingly ignored the novel object, spending little time investigating, and re-entering the nest box quickly. In contrast, rural birds spent more time reacting to the novel object and alarm calling within 5 m of the nest. When presented with a predator model, the urban birds reacted relatively more strongly (compared to the novel stimulus) than rural birds, spending more time within 5 m of the nest and alarm calling. These results suggest that either mountain chickadees in urban environments quickly acclimatize to the presence of novel objects or, potentially, that less neophobic birds disproportionately settle in urban environments or experience positive selection in urban areas. Either way, reduced neophobia may aid in mountain chickadees' ability to readily and successfully nest in such habitats.城市化正在重塑全球范围内的自然景观，迫使物种若要在城市环境中存续，必须快速完成驯化或适应。山地山雀（Mountain chickadee，*Poecile gambeli*）可在城市与乡村环境中顺利筑巢，且未表现出明显的繁殖成本。然而，城市筑巢的山地山雀能否在这类环境中成功存续，是否源于城乡个体的行为差异，目前尚未得到验证。我们在巢位处呈现新奇物体（novel object，即红色塑料杯）或模拟捕食者（simulated predator，即仿真松鼠模型），以此检测城乡筑巢山地山雀雌性个体的行为反应。行为反应同时取决于刺激模型类型与栖息生境。正如预期，山地山雀对松鼠模型的反应强度高于新奇物体；但反应差异的幅度则因生境而异。城市个体似乎对新奇物体毫无兴趣，仅花费极少时间进行探查，并快速返回巢箱。相较之下，乡村个体则会花费更多时间对新奇物体作出反应，并在巢位5米范围内发出警戒鸣叫（alarm calling）。当遭遇捕食者模型时，相较于新奇刺激，城市个体的反应强度相对更高：它们会在巢位5米范围内停留更久，并发出更多警戒鸣叫。上述结果表明，要么是城市环境中的山地山雀能够快速适应新奇物体的存在，要么是新物恐惧（neophobia）程度更低的个体更倾向于定居城市环境，或是在城市区域中受到了正向选择。无论何种机制，新物恐惧的降低或许有助于山地山雀在这类生境中顺利且成功地筑巢。