Predator-specificity of eastern gray squirrel alarm signals differs across sensory modalities

Background/Question/Methods

Studies of predator-specific alarm signals in birds and mammals have focused on vocalizations, but in eastern gray squirrels alarm signals include both vocalizations and tail signals. Their tail signals include small “twitches” and large “swishes.” Their alarm vocalizations include short broadband “kuks,” long broadband “quaas,” and narrowband “moans.” To test whether vocal and tail signals of gray squirrels differ with predator type, I presented individually identified squirrels with a series of objects to simulate terrestrial and aerial threats.

Results/Conclusions

Gray squirrels use twitches as general alarms, but their larger swishes are strongly associated with terrestrial threats. They similarly use kuk and quaa vocalizations as general alarms, but moans are strongly associated with aerial threats. This multimodal alarm signal system with each modality providing a threat-specific signal is unique among alarm signaling systems described to date and highlights the need to consider multimodal signaling in future studies.