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Abstract:
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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. |