Submitted to: North American Symposium on Bat Research
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2001
Publication Date: N/A
Technical Abstract: As with numerous other characteristics of their ecology, behavior, and physiology, Brazilian free-tailed bats, Tadarida brasiliensis, show remarkable variability and plasticity in their echolocation calls. Earlier field and laboratory studies documented that Tadarida exhibit the whole range of echolocation signals excluding very long constant-frequency (CF) signals, found among all other Microchiropteran bats. Recordings fro radio microphone bat detectors at altitudes of up to 1000 meters over Texas document thousands of quasi-CF (QCF) calls at 19 to 23 kHz that can exceed 20 ms duration. These calls, which from all evidence are those of T. brasiliensis, appear to document the exception to the species' call repertoire. Typical search calls of T. brasiliensis recorded at ground level are CF and QCF at approximately 50 kHz and 10 ms in duration. Our observations and those of numerous other field researchers document that the search calls emitted by these bats near ground level are typically at 32 to 25 kHz. However, many calls recorded at ground level over corn and cotton fields where T. brasiliensis forage in great abundance, as well as calls recorded as high as 500 meters above the ground, exceed 10 ms duration, satisfy the definition of search calls, and approach 50 kHz. We are investigating whether these are also calls of T. brasiliensis, and, if so, what is their ecological context. Calls recorded from 32 light-tagged, hand-released T. brasiliensis document a diverse suite of calls, including frequency-modulated (FM) with several harmonics, FM tailing with CF, and short CF/FM.