Common urban birds continue to perceive predator calls that are overlapped by road noise

Recent studies suggest that songbird communication is negatively affected by anthropogenic noise. However, much of the current literature focuses on inter- and intra-sexual communication. Songbirds also use acoustic cues for many other functional behaviors. One example associated with fitness consequences is the identification of predatory threats through acoustic cues. To test the effect of anthropogenic noise on detection of acoustic cues, we compared the rates of seven anti-predator behavioral responses in urban dwelling songbirds foraging at bird feeders when exposed to playback of calls from predatory Cooper’s hawks under quiet conditions, and when overlapped with road noise. Only a single behavior, freeze response, decreased significantly when calls were overlapped with noise. However, freeze responses occurred in only a small percentage of playback trials, raising some question regarding the biological relevance of this observed difference. Overall, our results suggest that common urban songbirds are relatively successful at perceiving acoustic signals associated with predator presence. Whether this ability is commonplace amongst songbird species is unknown and warrants additional study. However, if this trait is not widespread, it may be an additional characteristic determining which bird species can inhabit noisy areas.

     

Urbanization alters fear behavior in black-capped chickadees

Urban landscapes contain a multitude of novel sensory stimuli, and urban dwelling animals, such as songbirds living near human dwellings, must quickly learn how to respond to these unfamiliar cues. When exposure reveals that a stimulus is associated with a cost, fearful behavior should increase. Conversely, neophobic fear should decrease when negative outcomes do not regularly follow the stimulus. Because exposure to anthropogenic stimuli is more common in birds that inhabit urbanized landscapes, their fear response patterns should more accurately reflect the risks associated with these stimuli. We conducted a series of feeder and playback experiments to explore whether urbanization altered black-capped chickadees’ (Poecile atricapillus) fear responses to model cats, humans, a novel object, and anthropogenic noise. We predicted that fearful responses to cat models would increase in birds as urbanization increased because negative interactions with cats are more common in the city. However, we expected urban birds to be less fearful of our other stimuli because fitness costs are absent or less severe. As predicted, the fear of cats increased with urbanization, but the fear of noise decreased - as indicated by willingness to visit a feeding station. Other stimuli were not associated with urbanization, which may be related to the use of county and city parks where human presence is relatively common. Nonetheless, our results suggest that plastic fear responses to novel stimuli may facilitate urban success in the black-capped chickadee. More generally, behavioral plasticity may indicate the ability of a species to thrive in the urban environment.