Overwintering Brazilian Free-Tailed Bats (Tadarida Brasiliensis) in Central Texas: Baseline Population Estimates and Microclimate Habitat Analysis
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Colonies of Brazilian free-tailed bats (Tadarida brasiliensis) roost in central Texas from March through November. These bats have historically migrated south in late fall leaving summer roosts unoccupied during winter. Recently, new overwintering populations have been discovered in central Texas. The objectives of my study were to confirm the presence or absence of overwintering free-tailed bat colonies at six summer roosts, conduct baseline population estimates, and evaluate temperature and absolute humidity of habitats with and without overwintering bats during winters of 2010-2011 and 2011-2012. I placed 3 Hygrochron iButton data loggers within each roost and 1 outside to monitor temperature and humidity hourly. I entered each roost once a month (November-February) to determine bat presence. I recorded digital images with a laser caliper at 2 roosts with overwintering Brazilian free-tailed bat populations. I analyzed and estimated population sizes using ImageJ software. I estimated population size at a bridge using crevice measurements combined with previously established roosting densities for bridges. I estimated the population at a bat house roost containing Brazilian free-tailed bats using the percentage of space occupied based on dimensions and previously established roosting densities for bat houses. Two roosts were vacant and treated as control sites. My results indicated a difference in temperature (P = 0.086) but not absolute humidity (P = 0.813) between unoccupied and occupied overwintering roosts (α = 0.10). The populations increased at all occupied roosts from 2010 to 2011. I also report the northern-most occurrence of overwintering Brazilian free-tailed bats known in Texas. Overall, these data may lead to a greater understanding of the natural history of Brazilian free-tailed bats and identification and protection of potential overwintering sites in central Texas.