HRISTOV, N.I.*; BETKE, M.; KUNZ, T.H.; Boston University; Boston University; Boston University: Assessment of Brazilian Free-tailed Bat (Tadarida brasiliensis) Populations Using Advanced Infrared Thermal Imaging

The Brazilian free-tailed bat (Tadarida brasiliensis) is widespread in the southwestern United Stated between March and October, where it typically roosts in caves, buildings and bridges, forming some of the largest aggregations of mammals known to mankind. Each night these bats emerge from their roosts to feed on enormous quantities of insects, providing one of the most impressive examples of a large scale insect control service to both natural and agroecosystems. Yet, despite their estimated impact on insect populations, the exact role of this species is poorly understood by the scientific community. The goal of our project is to develop and apply new empirical and analytical methods for the accurate and reliable census of large numbers of bats using advanced infrared thermal imaging. Bat emergences were monitored at 6 major colonies in Texas and New Mexico using high-performance infrared thermal cameras. Seasonal trends were followed monthly at 3 of these sites. Recordings of the nightly emergences were analyzed using adaptive visual recognition algorithms that automatically identify and track individual bats. We present the first accurate and reliable estimates of the number of Brazilian free-tailed bats at 6 locations in Texas and New Mexico. Our data indicate large fluctuations in the size of the colonies on a seasonal as well as daily basis. Some of these fluctuations reflect the migratory habits of these bats, but others may be linked to large-scale weather patterns and related insect availability. These results will be discussed in the context of multi-scale ecological and economic modeling as well as in developing plans for the protection of these bats as an important national resource.