Meeting Abstract

1.9  Sunday, Jan. 4  Bats Aloft: Variation in Echolocation Call structure at High Altitudes GILLAM, EH*; MCCRACKEN, GF; WESTBROOK, JK; JENSEN, ML; BALSLEY, BB; University of Regina, SK Canada; University of Tennessee, Knoxville; USDA, Agricultural Research Service, College Station, TX; CIRES, University of Colorado, Boulder; CIRES, University of Colorado, Boulder gillam2e@uregina.ca

Bats alter their echolocation calls in response to changes in ecological and behavioral conditions, but little is known about how they adjust their call structure in response to changes in altitude. This study examines altitudinal variation in the echolocation calls of Brazilian free-tailed bats, Tadarida brasiliensis, a species known to fly at altitudes above 1000 m. From 50.2 hrs of recordings, we analyzed 113 high-quality echolocation call sequences (1,049 calls) recorded from 0 to 862 m above ground level. Bats flying near the ground (0-30 m) used shorter, higher frequency calls compared to bats recorded at higher altitudes, an effect likely due to the greater levels of echo-producing clutter (i.e. vegetation, buildings) found near the ground. When ground-level recordings are excluded, bats continue to shift towards the use of longer duration, lower frequency calls with increasing altitude. We propose that the observed high-altitude changes in call structure are a response to increasing acoustic attenuation rates, and/or decreasing insect densities at higher altitudes.