Wild tree squirrels respond with multisensory enhancement to conspecific robot alarm behaviour.

Natural social communication in animals involves the use of multiple sensory channels but has traditionally been easier to study one channel at a time. As a consequence we know more about the simplified situation of unitary signal channels than we do about the natural situation in which these sources are integrated. Studies of single channels of communication underestimate, and can even misrepresent, the salience and meaning of messages that are normally communicated via multiple channels. However, new mechanical or robotic animal models allow us to test the meaning of multiple components of a signal, via multiple sensory channels. Being three-dimensional, they also allow these questions to be tested in natural field settings where ambient light may constrain other methods such as video playback. Robotic models have been successfully tested with wild amphibians, reptiles and birds. Here we show that a wild mammal, the eastern grey squirrel, Sciurus carolinensis, responds to a robotic model displaying alarm behaviour. Wild squirrels showed enhanced responses to multisensory, audio/visual signals of alarm compared to unisensory (either audio or visual) signals. This is significant for studies of the evolution of communication in that it underscores the importance of taking the complete signal into account, and it provides a method for studying multisensory communication in wild mammals. It is also important for studies of sensory integration, since the squirrels showed an enhanced behavioural response to multisensory signals, providing an overt parallel to brain mechanisms of other mammals that show neural enhancement to multisensory stimuli