Zoological Studies

Vol. 40 No. 4, 2001

Timing and Variation in the Emergence and Return of Mexican Free-tailed Bats, Tadarida brasiliensis mexicana

Ya-Fu Lee* and Gary F. McCracken

Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA

Ya-Fu Lee and Gary F. McCracken (2001) We investigated the timing and variation in evening emergence and dawn return of a maternity colony of Mexican free-tailed bats, Tadarida brasiliensis mexicana, in the summers of 1996 and 1997.  In both summers, the onset of evening emergences and the end of dawn returns correlated with sunset and sunrise, respectively.  Bats tended to emerge earlier in relation to sunset during late summer than in spring to early summer. Dawn returns ended progressively later in relation to sunrise through the season. Bats emerged much earlier and ended dawn returns later in 1996 than in 1997, coincident with a severe drought in spring to midsummer 1996.  Bat captures during different seasons at the cave entrance indicate that patterns of emergence and return were non-random with regard to age, sex, and reproductive classes of bats.  Higher proportions of reproductive females emerged earlier in the evening and returned later at dawn.  Non-reproductive and post-lactating females and males exhibited an opposite pattern. Higher proportions of juveniles tended to emerge earlier in the evening and to return earlier at dawn.

Key words: Activity patterns, Bats, Tadarida brasiliensis mexicana.

*Correspondence: Division of Forest Protection, Taiwan Forestry Research Institute, Taipei, Taiwan 10051, R.O.C. Tel: 886-2-23039978 ext. 2513. Fax: 886-2-27858059. E-mail: abramus@protect.tfri.gov.tw