Utilization of Southwestern Bat Caves by Terrestrial Carnivores

Abstract

Utilization of bat caves in the southwestern United States by terrestrial mammals was investigated. Raccoons (Procy-on lotor) and striped skunks (Me phitis mephitis) made considerable use of the caves, feeding on fallen bats at the entrances and within the caves. Ringtail cats (Bassariscus astutus), opossums (Didelphis virginianus) and other terrestrial mammals appeared to use the caves less extensively. There was evidence of raccoon denning in at least one cave. No evidence of any canids using the caves was found. INTRODUCTION Numerous reports in the literature cite incidental observations of associations between bats and other native fauna; frequently these are reports of predation on bats. Many such reports refer to reptiles (Stager, 1942; Barr and Norton, 1965; Mankins and Meyer, 1965), raptorial birds (Stager, 1941; Downing, 1961; Perry and Rogers, 1964), or other species (Martin, 1961; Elwell, 1962) feeding on bats or living in bat caves; but only a few reports refer to terrestrial carnivores' feeding on bats (Sperry, 1933; Constantine, 1967) and occasionally being seen in bat caves. This study was undertaken to learn more about the association that exists between large bat caves and native terrestrial carnivores of the southwestern United States. It seemed probable that predators seeking food might be attracted to caves, particularly during the warmer months when these caves are inhabited by large numbers of bats. In addition to providing food for the predators, the caves might also be used for shelter. MATERIALS AND METHODS The four caves studied-Bracken, James River, Ney and Davis Blowout-are multichambered caverns in limestone formations on the Edwards Plateau in central Texas. They were selected because they are known to harbor large bat populations in summer months (Davis et at., 1962). Mexican free-tailed bats (Tadarida brasiliensis mexicana) use these as nursery caves, and, between May and August, large numbers of lactating females and flightless suckling young are found in the caves. Lesser numbers of other free-tailed bats and bats of other species are frequently found in these caves during the warm months. Each cave has at least one entrance readily accessible to any terrestrial mammal. Bracken is approximately 12 miles W of New Braunfels, Comal Co., Texas. The summer bat population has 1 Rabies Control Unit, Viral Zoonoses Section, Viral Diseases Branch, Epidemiology Program, Center for Disease Control, U. S. Public Health Service, P. 0. Box 363, Lawrenceville, Georgia 30245. 2Las Cruces, New Mexico.