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

Abstract

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 (δ2H) 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 δ2H for inference of bat movements is that the relationship between δ2H 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 δ2H of hair (δ2Hhair) and long-term δ2H of growing-season precipitation (δ2HGSprecip) 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 δ2Hhair and δ2HGSprecip 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 δ2Hhair and δ2HGSprecip. These results establish the relationship between δ2Hhair and δ2HGSprecip for red bats, which is necessary for the use of δ2Hhair 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.

Geographic origins and population genetics of bats killed at wind‐energy facilities

“…, , Pylant et al. ), the specific months of precipitation that most strongly influence the food webs supporting them during the period of molt are unknown. Thus, we developed geostatistical models and maps of June–August δ 2 H‐precipitation (δ 2 H JJA ) values and mean annual δ 2 H‐precipitation (δ 2 H p ) values for North America using the online workspace IsoMAP (Bowen et al.…”

“…, Pylant et al. ), which provides a solid basis for using δ 2 H hair values to identify potential summering regions of individuals of unknown geographic origin. If turbine‐killed bats are primarily from populations that summer around wind‐energy sites, then deceased individuals should have δ 2 H values characteristic of local precipitation.…”

Red bat fatality: Geographic extents through deuterium and niche models

“…We chose deuterium for the isotopic analysis based on studies that focused on the correlation between δD k and δD p (Cryan et al , ; Fraser et al ; Ossa et al ; Plyant et al ). Plyant et al () found differences in the relationship of δD k and δD p in male and female red bats such that female red bats have a higher variance, which could be due to some females in the sample rearing young during that season and having different metabolic demands. Although a single equation could be used for both sexes, we decided that the R 2 of the combined equation (0.37) was not a large enough increase from the female's R 2 of 0.29 to choose it when the male's R 2 was 0.69 (Plyant et al ).…”

“…Plyant et al () found differences in the relationship of δD k and δD p in male and female red bats such that female red bats have a higher variance, which could be due to some females in the sample rearing young during that season and having different metabolic demands. Although a single equation could be used for both sexes, we decided that the R 2 of the combined equation (0.37) was not a large enough increase from the female's R 2 of 0.29 to choose it when the male's R 2 was 0.69 (Plyant et al ). Therefore, we converted the eastern red bat hair isotope values (δD h ) using 2 equations: for males, and for females, (Plyant et al ; Data S1, available online in Supporting Information).…”

“…The discrepancy of δD k and δD p ratios is caused by multiple fractionation events where hydrogen and its isotopes are unevenly integrated into tissues causing a discrimination of these isotopes throughout the food web (Bowen et al ). Several studies have developed equations that relate δD k to δD p (Cryan et al , Fraser et al , Ossa et al , Cryan et al , Plyant et al ), and the resulting δD p values can then be mapped onto a δD p isoscape (a series of precipitation isoclines), which narrows possible geographic extents latitudinally (north to south). However, a δD p isoscape does little to reduce the extent longitudinally (east to west).…”