Evaluation of stable isotopes as a tool to delineate geographic catchment areas of the little brown bat hibernacula in Western Upper Michigan

Kruger, Laura

It has been presumed that abandoned underground mines in Michigan's Western Upper Peninsula (WUP) are critical winter refuge for the little brown bat (Myotis lucifugus). The use of stable hydrogen, carbon and nitrogen isotope analysis of little brown bat hair was evaluated as a tool to estimate summering origins of hibernating adult male and female little brown bats from three mine hibernacula in the WUP. Little brown bats were sampled at summering locations within Pictured Rocks National Lakeshore, Apostle Islands National Lakeshore, and Grand Portage National Monument. Stable hydrogen isotopes proved to be the most useful for delineating potential mine catchment areas. Delineated potential catchment areas for each mine hibernaculum were concentrated to the south, suggesting Lake Superior serves as a partial migratory barrier. Sex-biased migration has been observed in migratory temperate species of bats. Although differences in variability between males and females at each mine were not significant, the presence of outlying stable hydrogen isotope values of two female little brown bats suggests some females may be migrating farther distances than males. Overall, the findings suggest that the mines sampled in this study are important hibernacula for little brown bats throughout the Great Lakes region. Stable isotope analysis of bat hair proves to be a promising new approach to determining migratory origins of hibernating bats in mines of the WUP; however, there are some limitations that need to be addressed in future research in order to improve the accuracy with which little brown bat hibernacula catchment areas can be predicted.

Evaluation of stable isotopes as a tool to delineate geographic catchment areas of the little brown bat hibernacula in Western Upper Michigan

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