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The recently discovered invasive fungus Pseudogymnoascus destructans has been implicated in the deaths of millions of cave-hibernating bats in North America since 2006. While the loss of these mammals is likely to cause disturbances in surrounding ecosystems, one possible outcome is the sudden availability of foraging opportunities for migratory bats, which have remained unaffected by the fungus. Recognizing the possibility of this scenario, I hypothesized that areas witnessing dramatic losses of once-common bat species – such as the little brown bat Myotis lucifugus – would have concomitant increases in activity of other bat species that had been rarely detected or observed in the same areas, such as the eastern red bat Lasiurus borealis. Assuming that these species use the same resources and that such resources are limited in availability, reduced competition would allow the numbers and periods of use to increase for the once-uncommon species – a phenomenon known as competitive release. To test my hypothesis, I repeated an acoustic study (Divoll, unpublished data) of foraging bats at two locations in Acadia National Park (ANP), Mount Desert Island (MDI), ME. I used Wildlife Acoustics SM2BAT ultrasonic recorders nightly from April through October 2013 to acoustically identify species and to quantify echolocation rates from sites at Jordan and Bubble Ponds in the park. These data were compared to recordings collected in the same months in 2010, one-and-a-half years prior to the detection of the fungus on little brown bats in Acadia (Connery et al, 2012). In addition, I compared meteorological conditions (average precipitation, temperature, and sky cover) between years to determine whether variations in echolocation activity could be attributed to changes in environmental conditions. Two recorders were used, one at Bubble Pond and one at Jordan Pond. There were no statistically significant differences in weather between 2010 and 2013; however, 51,206 bat echolocation events were recorded in 2013 and 113,579 events were recorded in 2010. Recorders at Jordan Pond failed at key times of bat activity, and statistically significant differences between migratory bats were not observed. However, at Bubble Pond, detection of echolocation calls from little brown bats dropped significantly from a monthly average of 1468 occurrences per night in 2010 to 37 in 2013 (t-test, p < 0.001), while recorded occurrences of eastern red bats increased from 16 calls per night per month in 2010 to 83 in 2013 (t-test, p < 0.001). These data are consistent with the competitive release hypothesis.
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