Northern Long-Eared Bat Roost Tree Characteristics 2015-2017
2018-12
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Northern Long-Eared Bat Roost Tree Characteristics 2015-2017
Published Date
2018-12
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University of Minnesota Duluth
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Technical Report
Abstract
Female northern long-eared bats (Myotis septentrionalis) give birth to a single young, which is raised in a maternity roosting colony in trees. Young are born and lactation occurs from mid-June through at least late July in Minnesota. Bat pups are unable to fly for 3-4 weeks after birth, so the adult females leave the young in the maternity roost while they forage.
We tracked bats with VHF radiotransmitters to their roosts each day. At dusk, field crews conducted emergence surveys to count the number of bats emerging and find the roost entrance. In total we found 238 day roost locations of 83 female northern long-eared bats across the forested region of Minnesota. We returned to each roost tree to measure habitat characteristics. Female northern long-eared bats roosted in at least 27 different tree species. Almost all of the roost trees were in upland forests. In northern Minnesota, aspen (Populus tremuloides) was most commonly used as roosts. In central Minnesota, maple (Acer spp.) and aspen trees were most commonly used, and in southern Minnesota, oak trees (Quercus spp.) were most commonly used as roosts. About 90% of roost trees were deciduous species, and 10% of roost trees were coniferous species. Roost trees were more decayed and larger in diameter than available trees. Northern long-eared bats most often roosted in cavities and crevices of trees, although some roosted under loose bark or where branches had broken off. Four roosts were in unoccupied buildings.
Each roost tree location buffer and random location was overlaid on NLCD, GAP, and LandFire cover type classifications to calculate percent of area in forest cover variables. Variables related to deciduous forest were characteristic of roost tree locations. The LandFire variable TreeDom was the best predictor variable for identifying potential maternity roost habitat at the landscape level. In the forested area of Minnesota, the 50th percentile of random locations had 55% tree cover on average, compared to 80% tree cover for the roost tree locations. The relationship held at smaller scales, which meant that we could create maps of habitat suitability for northern long-eared bat maternity roosts across the forested region of the state. Northern long-eared bats in southern Minnesota, with more development and agriculture, used roost tree locations in patches of forest. In northern Minnesota, roost trees were within forest stands instead of on the edges of forest stands, and roost trees tended to be located in areas with trees present in most of an 800 m foraging radius.
We also tracked 13 little brown bats and 8 big brown bats to roosts in trees and buildings. The 13 little brown bats were tracked to 12 roost trees of at least five species, and five roosts in buildings. The eight big brown bats were tracked to 13 roost trees of at least seven species, and two roosts in buildings. All bats with transmitters that roosted in buildings were females that were either pregnant or lactating
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Swingen, Morgan; Moen, Ronald; Walker, Marcus; Baker, Richard; Nordquist, Gerda; Catton, Timothy; Kirschbaum, Kari; Dirks, Brian; Dietz, Nancy. (2018). Northern Long-Eared Bat Roost Tree Characteristics 2015-2017. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/204334.
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