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

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