Population dynamics of Leptonycteris curasoae (Chiroptera: Phyllostomidae) in Jalisco, Mexico

We estimated population size and sex ratio, and recorded mass, levels of fat, and reproductive condition of adults of Leptonycteris curasoae living in a sea cave in Chamela Bay, Jalisco, Mexico, 10 times between October 1992 and February 1994. We used carbon and nitrogen stable-isotope techniques to determine the general diet of this plant-visiting bat in 1993 and 1994. Size of roost in 1993 varied from ca. 5,000 individuals in March to ca. 75,000 in November. Females were absent from, or uncommon in, the roost from March through September. Beginning in July or August, many males and females migrated to the roost; bats left the roost in December. Some of these females migrate north to the Sonoran Desert to form maternity colonies in spring. Size of testis increased markedly from October through December, which we postulate is a mating period in this roost, Bats were lean in April and June (dry season) and fat in October and November (end of wet season). Stable-isotope analysis revealed that bats fed primarily at nonsucculent (C3) plants throughout the year; values for nitrogen were higher in the wet season than in the dry season. From a review of data on other roosts of L. curasoae, we conclude that most roosts have a seasonal fluctuation in size and sexual composition. We also postulate that two reproductive populations of females exist in Mexico; a spring-birth population and a winter-birth population. Seasonal fluctuations in size of roost mean that the timing of visits to the roost is critical for assessing the population status of this federally listed endangered bat.