Print PageBrazilian free-tailed bats (Tadarida brasiliensis) are one of the most abundant, wide ranging mammal species in North America. From March through October, numerous colonies of free-tailed bats roost in central Texas. Historically, these bats migrate south in October leaving their summer roosts unoccupied during the winter. Recently, overwintering populations have been discovered in central Texas. This behavioral change may be related to multiple factors, including global climate change. Because this phenomenon is relatively new, minimal survey and environmental data have been collected on overwintering populations of free-tailed bats in central Texas. The objectives of my study are to confirm the presence or absence of overwintering (November-February) free-tailed bat colonies at six sites known to be summer roosts, and evaluate temperature and humidity of habitats with and without overwintering bats during the winter seasons of 2010-2011 and 2011-2012. I placed 3 Hygrochron iButton data loggers within each site and 1 outside to monitor temperature and humidity hourly. Each site was entered once a month to determine if bats were present. Study sites included Bracken Bat Cave, the Chiroptorium (Bamberger Ranch), Davis Blowout Cave, D’Hanis Bridge, James River Bat Cave, and Old Tunnel.
Results/Conclusions
Bracken Bat Cave, the Chiroptorium, D’Hanis Bridge, and Old Tunnel were determined to have overwintering populations. Davis Blowout Cave and James River Bat Cave were vacant and treated as control sites. One way ANOVAs were performed on the weekly mean temperature and relative humidity of the sites to determine if significant differences existed between sites with bats and our control sites. The results showed a difference in both the temperature (F=19.27; df=1, 86; P<0.001) and the relative humidity (F=9.536; df=1, 86; P=0.003). The overall mean temperature of sites containing bats versus our control sites were 12.2°C and 15.5°C, respectively. The overall mean relative humidity of sites containing bats versus our control sites were 72.8% and 59.8%, respectively. Our results indicate that free-tailed bats are selecting for sites with lower temperatures and higher humidity. Winters in central Texas can be quite harsh with temperatures falling below freezing. Overwintering free-tailed bats would likely utilize torpor during these periods and would therefore benefit from colder sites with higher humidity for energy conservation. Overall, these data may lead to a greater understanding of the natural history of free-tailed bats and identification and protection of possible overwintering sites in central Texas.
