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United States Department of Agriculture

Agricultural Research Service

Research Project: ECOLOGICALLY-BASED MANAGEMENT OF BOLL WEEVILS AND POST-ERADICATION CROP PESTS Title: Bats aloft: Variation in echolocation call structure at high altitudes

Authors
item Gillam, Erin - UNIV OF REGINA, CANADA
item Mccracken, Gary - UNIV OF TENNESSEE
item Westbrook, John
item Jensen, Michael - UNIV OF COLORADO
item Balsley, Ben - UNIV OF COLORADO

Submitted to: Behavioral Ecology-Sociobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 23, 2009
Publication Date: July 17, 2009
Citation: Gillam, E.H., McCracken, G.F., Westbrook, J.K., Jensen, M.L., Balsley, B.B. 2009. Bats aloft: Variation in echolocation call structure at high altitudes. Behavioral Ecology-Sociobiology. 64:69-79.

Interpretive Summary: Bats alter their echolocation calls in response to changes in ecological and behavioral conditions, but little is known if they adjust the characteristics of their calls at different altitudes. This study examines altitudinal variation in the echolocation calls of the Brazilian free-tailed bat (Tadarida brasiliensis), a species known to fly at altitudes above 1000 m. From more than 50 hours of ultrasonic recordings, we found that bats flying near the ground used shorter, higher frequency calls compared to bats recorded at higher altitudes. The frequency effect was likely due to greater levels of echoes produced by clutter from vegetation, buildings, and other structures near the ground. Excluding ground-level recordings, bats continued to shift towards the use of longer duration, lower frequency calls with increasing altitude. These results will aid in the understanding of bat feeding flights, especially those during which they disperse over large regions to feed on insect pests of crops.

Technical Abstract: 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.

Last Modified: 12/21/2014
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