Population Structure and Dynamics of Juvenile Brazilian Free-tailed Bats (Tadarida brasiliensis mexicana) Banded in Central Texas

Abstract

During the summer months as many as 3 million Brazilian free-tailed bats (Tadarida brasiliensis mexicana) reside in an abandoned train tunnel at the Old Tunnel Wildlife Management Area, Kendall County, Texas. This study examined the population ecology of juvenile bats as it related to emergence patterns, sex ratios, and recruitment. To collect large numbers of bats efficiently a 1.8 m by 2 m double frame Harp trap was lowered in front of the south opening of the tunnel shortly after the start of the emergence. Banding occurred in late July and August of 1999 and 2000. Bands were placed on 4,000 and 3,625 bats, respectively. The sex of each juvenile banded and the dates of banding were recorded. Capture data showed no significant difference in the sex ratio in 1999, however the ratio was significantly male biased (p < 0.001) in 2000. Data from recaptures were analyzed using the Jolly-Seber method to estimate the juvenile population for both summers. Results show a decrease in the population from 1999 to 2000. Population trends, however, appear to be similar between the two summers.