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Offshore wind energy in the U.S. is a growing industry, and there is concern that offshore turbines may impact bats that migrate over the ocean. We reviewed the literature to synthesize historic and contemporary accounts of bats in the marine environment to better understand which North American species have the highest exposure risk from offshore wind development, and when and where we might expect the highest fatalities to occur at sea.
Bat activity surveys to predict risk at wind farms have long been the industry standard. We found no relationship between bat echolocation rates and bat fatality rates at 49 wind farms across the U.S. and Canada, changing the landscape of the consulting world. This research is saving wind energy clients tens of thousands of dollars on surveys that do not work, allowing them to put that money towards more effective risk assessment methods.
The known distributions of eastern red bats and western red bats in western North America have changed greatly over the past 2 decades, resulting in inaccurate range maps and uncertainty regarding the presence or probable absence of these species within states and provinces. We obtained capture and specimen records from the western United States and Canada for 276 eastern red bats and for 863 western red bats. We documented the expansion of the range of eastern red bats in northwestern Canada and clarified the northern and eastern limits of western red bat distribution in the United States.
While various identification models have been studied extensively, there has been little study of methods for selecting bat calls prior to modeling or methods for validating results after modeling. We obtained two call libraries for 11 North American bat species. We used four acoustic filters to automatically select and quantify bat calls from the combined library. We found that filters affect every stage of echolocation identification, and that the composition of call libraries affected estimates of correct classification rates. We recommend that researchers carefully design and test filters and include adequate descriptions in publications, and caution that it may not be possible to extend inferences about model accuracy beyond the training call library.
In the journal Bat Research News, we describe the unusual occurrence of finding intertwined carcasses of two eastern red bats that had apparently died while mating. Red bats initiate mating on the wing and drop to the ground to consummate the act. We propose that this pair died due to falling from a great height onto a hard, paved parking lot, and indicate this may be an increasing source of mortality in an increasingly paved world.
The costs and beneﬁts of torpor for bats may vary across their range, resulting in different thermoregulatory behaviors. We compared torpor use and roosting behavior for female western long-eared bats in the mountains and prairies of Alberta. We found that females in the mountains minimized their use of torpor and selected exposed roosts with warm microclimates during pregnancy, and then switched to clustering with other individuals during lactation when conditions were cooler. In the prairies, females roosted alone in cooler, less exposed roost types and spent more time in torpor. Our results illustrate the importance of considering geographic variation in behavior across the range of a species.
We compared the external morphology of western long-eared bats living in mountain (cool, wet) and prairie (warm, dry) environments in southern Alberta to test whether ﬂight permits genetic exchange between populations thereby limiting divergence in morphological traits. Ears and wings were signiﬁcantly larger for bats in the mountains,suggesting that there is limited gene ﬂow between populations despite their geographic proximity, and adaptation to differences in aridity or foraging habitat. However, body size was similar between environments, suggesting that either bats possess an ecologically ﬂexible body type or that differences in extremity size are the result of environmentally induced phenotypic plasticity.
Entering torpor can yield significant energy savings for temperate-zone bats but can be costly for reproductive females by slowing fetal development and reducing milk production. We studied western long-eared bats in the Rocky Mountains of Alberta and found that bats entered torpor frequently, but nonreproductive females spent longer periods in torpor. Reproductive females roosted in crevices that warmed rapidly and reached warm daytime temperatures. Females roosted alone during pregnancy but formed small colonies within roosts during lactation when ambient conditions were cooler. Nonreproductive females roosted alone in crevices in the ground.These roosts had cooler, more stable microclimates, allowing females to enter deeper bouts of torpor and remain torpid longer