Patterns of activity and fatality of migratory bats at a wind energy facility in Alberta, Canada

Abstract

Studying migratory behavior of bats is challenging. Thus, most information regarding their migratory behavior is anecdotal. Recently, however, fatalities of migratory bats at some wind energy facilities across North America have provided the opportunity and impetus to study bat migration at fine spatial and temporal scales. Using acoustic monitoring and carcass searches, we examined temporal and spatial variation in activity levels and fatality rates of bats at a wind energy facility in southern Alberta, Canada. Our goals were to better understand the influence of weather variables and turbine location on the activity and fatality of hoary bats (Lasiurus cinereus) and silver‐haired bats (Lasionycteris noctivagans), and to use that understanding to predict variation in fatality rates at wind energy facilities and recommend measures to reduce fatalities. Overall activity of migratory bats and of silver‐haired bats increased in low wind speeds and warm ambient temperatures, and was reduced when the wind was from the North or Northeast, whereas hoary bat activity increased with falling barometric pressure. Fatalities of migratory bats in general increased with increased activity of migratory bats, increased moon illumination, and falling barometric pressure and were influenced by the interaction between barometric pressure change and activity. Fatalities of silver‐haired bats increased with increased activity, moon illumination, and winds from the south‐east. Hoary bat fatalities increased with falling barometric pressure. Our results indicate that both the activity and fatality of migratory bats are affected by weather variables, but that species differ in their responses to environmental conditions. Spatially, fatalities were not influenced by the position of turbines within a turbine row, but were influenced by the location of turbines within the facility. Our findings have implications for our understanding of bat migration and efforts to reduce fatalities at wind energy facilities. To maximize the reduction of bat fatalities, operators of wind energy facilities could incorporate migratory bats' response to environmental variables, such as barometric pressure and fraction of moon illuminated, into their existing mitigation strategies. © 2011 The Wildlife Society.

Behavior of bats at wind turbines

“…Bats rely on vision for long-distance orientation (23)(24)(25), are known or suspected to orient through landscapes using light cues, such as stars and postsunset glow (26,27), and use visual cues to help them find roosts in trees (28). The effects of moonlight on bat activity and fatality at turbines are not well understood, but a study in Alberta, Canada, reported higher fatality rates of silver-haired bats (Lasionycteris noctivagans) at wind turbines on nights when the moon was fully illuminated (29). There is no evidence that tree bat activity in the absence of, or distant from, turbines varies with lunar cycles or illumination (30).…”

Origins and migratory patterns of bats killed by wind turbines in southern Alberta: evidence from stable isotopes

“…There v www.esajournals.org appears to be some degree of sexual segregation during summer, with females potentially migrating greater distances than males (Findley and Jones 1964, Cryan 2003, Cryan et al 2004. Although their distribution is unknown, the relatively high proportion of adult male hoary bat fatalities at wind energy installations in Alberta (Baerwald and Barclay 2011) suggests that more adult males move into the province than previously suspected. In Alberta, 54% of bat fatalities at wind energy installations are hoary bats (E. F. Baerwald, unpublished data).…”

“…We thus predicted that the isotope values in the fur of adult females are lower than those of adult males, reflecting the longer, more northern migration made by females. Based on capture and fatality records (Baerwald and Barclay 2011), we further predicted that the degree of sexual segregation, thus the difference in isotope values between males and females, is greater in hoary bats. Finally, to explore the temporal patterns of bat migration, we examined the relationship between isotope values and date.…”

“…Given that hoary and silver-haired bats differ in size, morphology, and roosting and foraging behavior, and thus likely differ in their optimal migration strategies (Barclay 1985, Hedenstrom 2008, 2009, Baerwald and Barclay 2011, our underlying hypothesis was that these differences influence their distribution and migration, which would be reflected in the isotopic signature of their fur. We thus predicted that the stable isotope values present in the fur of hoary and silver-haired bats differ.…”

“…We thus predicted that the stable isotope values present in the fur of hoary and silver-haired bats differ. Based on published range maps, inferred migratory behavior (Barclay 1984, Cryan 2003, and the seasonal timing of fatalities (Baerwald and Barclay 2011), we specifically hypothesized that (1) bats killed at turbines in southwestern Alberta are migrants (i.e., not local) and that (2) hoary bats originate from farther north and from a broader range than silver-haired bats do. If bat fatalities at turbines represent migrants, we predicted that both the variance and the mean isotope values of their fur are greater than the isotope values in the fur of resident bats (i.e., fur collected from bats on their summering grounds) from the same latitude as the wind energy facilities.…”