Urban junco flight initiation distances correlate with approach velocities of anthropogenic sounds

Urban-dwelling birds face novel visual cues and soundscapes. To thrive in these challenging environments, individuals must correctly identify and calibrate threats posed by humans and their activities. We showed that Dark-Eyed Juncos (Junco hyemalis) residing in an urban habitat responded differently to the sounds that approaching people and objects make. A person approached juncos simultaneously playing the sounds of object types that normally move at different relative velocities: faster (bicycles), intermediate (skateboards and scooters), or slower (people walking). Juncos responded at significantly greater distances and moved further in relation to what sound cues would normally imply about the velocity of approach. Absolute stimulus volume was not a significant predictor of response across object type. The responses occurred without the presence of visual cues, suggesting that an auditory cue alone and without visual confirmation can produce an appropriate response. Overall, this shows that this population of urban juncos has the ability to respond appropriately to novel anthropogenic sound cues. The question remains as to how universal such abilities are across species, different urban situations, and in natural habitats.

栖息于城市环境的鸟类会面临全新的视觉信号与声景。为在这类充满挑战的环境中繁衍生息，个体必须准确识别并研判人类及其活动所构成的威胁。我们的研究显示，栖息于城市生境的暗眼灯草鹀（Dark-Eyed Juncos，Junco hyemalis），对接近的人类及物体所发出的声响会产生差异化反应。实验中，当人类向灯草鹀靠近时，同步播放三类通常以不同相对速度移动的物体的声响：快速移动的物体（自行车）、中等速度移动的物体（滑板与踏板车），以及慢速移动的物体（步行的人类）。相较于这些声响线索通常所暗示的接近速度，灯草鹀的避险反应距离显著更远，且移动幅度也更大。在不同物体类型间，刺激声的绝对音量并未对反应情况产生显著影响。此类反应在无视觉线索的情况下即可触发，这表明仅依靠听觉线索、无需视觉佐证，就能引发恰当的避险反应。综上，该结果表明，这一城市生境的暗眼灯草鹀种群，能够对新型人为活动声响线索做出恰当的响应。但仍有问题有待解答：这类能力在不同物种、不同城市环境以及自然生境中，其普遍性如何。