Multimodal alarm behavior in urban and rural gray squirrels studied by means of observation and a mechanical robot

Urbanization of animal habitats has the potential to affect the natural communication systems of any species able tosurvive in the changed environment. Urban animals such as squirrels use multiple signal channels to communicate, but it is unknownhow urbanization has affected these behaviors. Multimodal communication, involving more than one sensory modality,can be studied by use of biomimetic mechanical animal models that are designed to simulate the multimodal signals and be presentedto animal subjects in the field. In this way the responses to the various signal components can be compared and contrastedto determine whether the multimodal signal is made up of redundant or nonredundant components. In this study, we presentedwild gray squirrels in relatively urban and relatively rural habitats in Western Massachusetts with a biomimetic squirrel modelthat produced tail flags and alarm barks in a variety of combinations. We found that the squirrels responded to each unimodalcomponent on its own, the bark and tail flag, but they responded most to the complete multimodal signal, containing both theacoustic and the moving visual components, providing evidence that in this context the signal components are redundant and thattheir combination elicits multimodal enhancement. We expanded on the results of Partan et al. (2009) by providing data on signalingbehavior in the presence and absence of conspecifics, suggesting that alarm signaling is more likely if conspecifics arepresent. We found that the squirrels were more active in the urban habitats and that they responded more to tail flagging in theurban habitats as compared to the rural ones, suggesting the interesting possibility of a multimodal shift from reliance on audio tovisual signals in noisier more crowded urban habitats [Current Zoology 56 (3): 313-326, 2010].

Urbanization of animal habitats has the potential to affect the natural communication systems of any species able to survive in the changed environment. Urban animals such as squirrels use multiple signal channels to communicate, but it is un- known how ttrbanization has affected these behaviors. Multimodal commtmication, involving more than one sensory modality, can be studied by use of biomimetic mechanical animal models that are designed to simulate the multimodal signals and be pre- sented to animal subjects in the field. In this way the responses to the various signal components can be compared and contrasted to determine whether the multimodal signal is made up of redundant or nonredundant components. In this study, we presented wild gray squirrels in relatively urban and relatively rural habitats in Western Massachusetts with a biomimetic squirrel model that produced tail flags and alarm barks in a variety of combinations. We found that the squirrels responded to each unimodal component on its own, the bark and tail flag, but they responded most to the complete multimodal signal, containing both the acoustic and the moving visual components, providing evidence that in this context the signal components are redundant and that their combination elicits multimodal enhancement. We expanded on the results of Partan et al. （2009） by providing data on sig- naling behavior in the presence and absence of conspecifics, suggesting that alarm signaling is more likely if conspecifics are present. We found that the squirrels were more active in the urban habitats and that they responded more to tail flagging in the urban habitats as compared to the rural ones, suggesting the interesting possibility of a multimodal shift from reliance on audio to visual signals in noisier more crowded urban habitats [Current Zoology 56 （3）： 313-326, 2010].