Individual Variation In The Echolocation Calls Of Big Brown Bats Eptesicus Fuscus And Their Potential For Acoustic Identification And Censusing PDF Download

Bats are well-known for their ability to echolocate for orienting and foraging in the dark, but many bat species also produce other vocalizations in the presence of conspecifics. Such vocalizations may be used to avoid in-flight collisions, attract mates, defend territories, or facilitate group cohesion. The association between many of these vocalizations and their behavioral context is unknown. I used big brown bats (Eptesicus fuscus) as a model system to explore the communicative potential of these vocalizations and the behavioral context under which they are produced. Big brown bats were collected from two locations (Gorham, New Hampshire and Vershire, Vermont) and individual (n=12) and paired (n=10) bats were released inside an enclosure. Audio and video data were simultaneously collected to relate in-flight behavior with vocalizations. Bats in paired trials produced significantly more non-echolocation vocalizations, suggesting that these may serve a communicative function. A total of 915 putative communication calls were extracted from 10 paired trials and acoustic measurements were made. Twelve spectral and temporal parameters were measured for each call, and data were grouped as similar or dissimilar using hierarchical cluster analysis (HCA). The HCA grouped the data as 8 clusters, each cluster representing a unique call type. A principal components analysis (PCA) was run to determine the degree of acoustic dissimilarity across clusters representing call types. Results from PCA did not show discrete call categories. Overlap in the acoustic characteristics of call types was observed, suggesting that communication calls of big brown bats may be continuous and not discrete signal. Behavioral observations generated 29 detailed behavior categories which were further merged into 7 broad behavior categories. Larger clusters were associated with all broad categories, whereas smaller clusters were associated with some but not all broad behavior categories. Some calls that were grouped as 'cluster 7' were part of a call set and were mostly associated with the behavior category where both bats were perched. These calls were also longer in duration and lower in frequency, suggesting that bats may be using these acoustic features to communicate when perched. Many calls in 'cluster 8' that consisted of high frequency and short duration calls, was associated with the behavior category where one bat was flying close to a perched bat, suggesting that these calls might be used by bats in proximity.