Stable hydrogen isotopes record the summering grounds of eastern red bats (Lasiurus borealis)

Bats face numerous threats associated with global environmental change, including the rapid expansion of wind-energy facilities, emerging infectious disease, and habitat loss. An understanding of the movement and migration patterns of these highly dispersive animals would help reveal how spatially localized the impacts from these threats are likely to be on bat populations, thus aiding in their conservation. Stable hydrogen isotope ratios (δ(2)H) can be used to infer regions where bats have foraged during the summer molt season, thus allowing an assessment of summering location and distance of movement of bats sampled during other times of year. However, a major impediment to the application of δ(2)H for inference of bat movements is that the relationship between δ(2)H of bat hair and precipitation tends to be species specific and is still unknown for some key species of conservation concern. We addressed this issue by using geo-referenced museum specimens to calibrate the relationship between δ(2)H of hair (δ(2)H(hair)) and long-term δ(2)H of growing-season precipitation (δ(2)H(GSprecip)) at the site of collection for eastern red bats (Lasiurus borealis), one of the main species of bats experiencing large numbers of fatalities at wind-energy facilities in North America. Based on comparison of δ(2)H(hair) and δ(2)H(GSprecip) values for males we estimated a period of molt of June 14–August 7. Within this period, male and female red bats exhibited a significant positive relationship between δ(2)H(hair) and δ(2)H(GSprecip). These results establish the relationship between δ(2)H(hair) and δ(2)H(GSprecip) for red bats, which is necessary for the use of δ(2)H(hair) to infer the movement and migration patterns of this important species. These results provide a critical resource to conservation biologists working to assess the impacts of environmental change on bat populations.