Population structure of migratory Mexican free-tailed bats Tadarida brasiliensis mexicana (Chiroptera) in a Chihuahuan Desert roost
Lopéz-González, CeliaRascón, JorgeDaniel Hernández-Velázquez, Francisco
Cueva del Guano, located in the state of Durango, northern Mexico, is inhabited by a colony of migratory Mexican free-tailed bats and it is located within one of the proposed migratory paths. To document the use bats make of this cave and its importance as a refuge for migratory populations, we observed, sampled, banded, and released bats monthly for 26 months in 2005-2008 to 1) estimate population size and fluctuations using counts at emergence time and mark-recapture data, and 2) determine sex ratio, relative age, and reproductive condition of random samples of 100 individuals. The cave is occupied year-round by T. brasiliensis, with population size ranging from at least 2,524 bats in March to at least 19,360 in September. Sex ratio, age structure, and reproductive condition suggest that the cave is used by two discrete groups of free-tailed bats; one that resides year-round in the cave and another (mostly females) that uses it as a transient roost in spring and autumn. Evidence of two migratory groups occupying the same roost at least part of the year points to the existence of a complex system of interactions among migratory populations.