Variation in body temperature and isolation calls of juvenile big brown bats, Eptesicus fuscus

As occurs in some poikilotherms, the acoustic signals of young birds and mammals may be influenced by ambient temperature because young cannot maintain a constant body temperature. This may have consequences in colonial species in which individual recognition of offspring by parents is important if care is to be directed appropriately. In bats, mothers use isolation calls of pups to locate their own infants. For isolation calls to function effectively for individual recognition, they must vary among individuals while remaining relatively consistent for any given individual. We investigated the effect of variation in body temperature on the isolation calls of the big brown bat. Young pups are unable to thermoregulate and thus experience a wide range of body temperatures, potentially affecting their ability to produce consistent vocalizations. We recorded the isolation calls of pups at different body temperatures and measured various characteristics of the calls. Pups produced isolation calls at body temperatures ranging from 11 to 37°C. However, with increasing body temperature, the isolation call frequencies as well as the call interval decreased, while call duration increased, but changes in call structure with body temperature were not consistent among individuals. Overall, isolation calls produced at various body temperatures were identified no more accurately via discriminant function analysis when body temperature was accounted for than when it was not. Isolation calls produced by different individuals at approximately the same body temperature were classified most accurately (79%). Variation in body temperature of young therefore has the potential to hinder individual recognition by mothers in colonial situations. Other identification cues, such as odour and spatial memory, may be important.