Animals in urban areas that experience frequent exposure to humans often behave differently than those in less urban areas, such as exhibiting less vigilance or anti-predator behavior. These behavioral shifts may be an adaptive response to urbanization, but it may be costly if animals in urban areas also exhibit reduced anti-predator behavior in the presence of natural predators. In trials with only a human observer as the stimulus, urban squirrels exhibited reduced vigilance and anti-predator behavior compared to those in less urban areas. Next, we exposed squirrels in multiple urban and less urban sites to acoustic playbacks of a control stimulus (non-predatory bird calls), a natural predator (hawk), and dogs and recorded their vigilance and three different anti-predator behaviors when a human approached them while either broadcasting one of these three playbacks or no playbacks at all. Squirrels at urban sites also did not differ in their behavioral responses to the playbacks from possible predators (hawks or dogs) when they were compared to those at less urban sites exposed to these playbacks. Urban squirrels also exhibited increased vigilance and anti-predator behavior when exposed to a human paired with hawk playbacks compared to the control playbacks. Together, our results indicate that urban squirrels did perceive and assess risk to the natural predator appropriately despite exhibiting increased tolerance to humans. These results provide little support for the hypothesis that increased tolerance to humans causes animals to lose their fear of natural predators.

中文翻译：

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城市狐狸松鼠对人类表现出耐受性，但对天敌的刺激做出反应

经常接触人类的城市地区动物的行为通常与不太城市地区的动物不同，例如表现出较低的警惕性或反捕食者行为。这些行为转变可能是对城市化的一种适应性反应，但如果城市地区的动物在有天敌存在的情况下也表现出减少的反捕食者行为，那可能代价高昂。在仅以人类观察者为刺激的试验中，与城市地区较不发达地区的松鼠相比，城市松鼠表现出的警惕性和反捕食行为降低。接下来，我们将多个城市和非城市地点的松鼠暴露于控制刺激（非掠食性鸟类的叫声）、天敌（鹰）、当人类接近它们时，记录它们的警惕性和三种不同的反捕食者行为，同时播放这三种回放中的一种或根本没有回放。与那些暴露于这些回放的较不城市地点的松鼠相比，城市地点的松鼠对可能的捕食者（鹰或狗）的回放的行为反应也没有差异。与对照回放相比，城市松鼠在暴露于人类与鹰回放时也表现出更高的警惕性和反捕食者行为。总之，我们的结果表明，尽管城市松鼠对人类表现出更高的耐受性，但它确实能够适当地感知和评估对天敌的风险。