Variation in search-phase calls of bats

Abstract

Although echolocation calls of most bats exhibit species-specific characteristics, intraspecific variation can obscure differences among species and make reliable acoustic identification difficult. We examined levels of intraspecific variation in search-phase calls of 7 species of vespertilionid bats from several locations in the eastern and central United States. Echolocation calls were recorded from light-tagged bats using the Anabat II detector and associated software. Analook software was used to calculate values for 5 parameters of calls: duration, maximum frequency, minimum frequency, frequency of the body, and slope of the body. Analysis of our results indicates that most intraspecific variability in calls was attributable to differences among individuals and within individual call sequences. Observed levels of geographic variation, although significant in all species examined, were comparatively small and showed no trends among areas. We include a preliminary description of variability in echolocation calls of Nyticeius humeralis and Myotis leibii.