Population Dynamics of the Big Brown Bat (Eptesicus fuscus) in Southwestern Ohio

Abstract

Population dynamics of the big brown bat ( Eptesicus fuscus ) were studied for four years (1969–1972) in southwestern Ohio. Data were collected from 10,761 banded bats located in 81 summer nursery colonies and five winter hibernacula. Of 4506 immature big brown bats captured during the study period, 2223 (49.3 percent) were females. Contrary to previous studies, adult females outnumbered males in three of five winter hibernacul. Tooth wear of known age bats predicted population age class structure, but was a poor indicator of a specific age of a given individual. Survivorship curves for female bats were constructed from the percentage of banded individuals which were recaptured in subsequent years within the nursery colonies. Annual female mortality rate values for two large bat populations were 68.1, 28.7, and 72.0 percent and 89.5, 30.0, and 42.9 percent, respectively. Big brown bats recaptured at distances greater than 8 kilometers (km) (5 miles, mi) from the home colony were found to move in a southerly direction. In two instances record natural movements of 250 km and 290 km (155 and 180 mi) were recorded for E. fuscus . Larger populations of Eptesicus were located in the unglaciated region of the study area. Efficiency of young production per adult female was found to decrease with a corresponding increase in nursery population size. Merits of this inverse correlation efficiency as a potential population regulatory mechanism are discussed.