Stable isotope analysis of a behaviorally novel colony of Tadarida brasiliensis mexicana (Brazilian Free-tailed Bat) in West Texas
Miller, Jennifer Jean
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The objective of this research is to evaluate the status of a colony of Tadarida brasiliensis mexicana (the Brazilian Free-tailed Bat, also known as the Mexican Freetailed Bat) in west Texas. Populations of Tadarida brasiliensis mexicana are thought to be migratory in the central and southwest regions of the United States, but a roosting location in west Texas has been observed to have year-round emergences. This behavior is contradictory to the published literature. Hydrogen stable isotope analysis of hair samples was used to determine whether this roost supports a stationary colony or whether it is being used by a number of transient populations throughout the year. Statistical analysis was used to create individual probability maps for analyzed stable isotope values. These maps used predicted hydrogen stable isotopes to assign possible molting locations of sampled individuals based on both sample month and growing season. Although low temperatures and structural restraints prevented the sampling of individuals during the December 2009 to February 2010, bats were observed or heard in the roost every month. Visual observations and statistical analysis of analyzed stable isotope values confirm that the colony is composed of a number of transient populations. Additionally, the documentation of Tadarida brasiliensis mexicana roosting year-round in west Texas is the first documentation of such behavior in this region. This location represents the northern-most latitude in which this subspecies has been found during the winter and may be an indication of extending winter range and/or behavioral changes.