Living on the edge: Habitat characteristics of northern myotis at the periphery of its distribution
- Melhuish, Jacob J. E. [ Montana State University: Ecology ]
- Litt, Andrea R. [ Montana State University: Ecology ]
- Borgreen, Michael J.
- Harris, Heather F.
Populations at the edge of their distribution may occur in places with atypical and more variable conditions than at the core of the range. We characterized habitat selection for the northern myotis (Myotis septentrionalis) at the western edge of its known distribution in the United States, comparing roost selection to other peripheral populations and core populations. We focused on summer daytime roosts, which provide refuge while bats give birth, raise young, and prepare for hibernation or migration. We captured bats from May-August in 2022 and 2023 and attached transmitters to 36 northern myotis. We located 76 roosts from 33 tagged individuals and characterized roost (used) trees and the surrounding patch, comparing these with random (available) locations. Our findings support the notion that northern myotis select roosts based on characteristics of the tree and the surrounding patch, choosing areas that provide multiple possible roosts. Northern myotis showed strong associations with tall trees in patches having a relatively high average basal area that contained multiple trees similar to the roost tree; results are consistent with previous research. Bats roosted primarily in eastern cottonwoods (Populus deltoides; 97% of roosts), which was the most available tree species on the landscape, yet this species has been used infrequently in other studies. Bats selected cottonwoods in early stages of decay with somewhat less canopy cover, whereas other studies in the core of the distribution have documented extensive use of snags and decaying trees; this difference was likely due to limited availability of later decay stages in our study area. Most consecutive roosts were relatively close together (range = 2-881 m) and each roost was used for 1.7 days on average (range = 1-7). In this landscape, large trees were mainly found in narrow linear bands along riparian corridors within an agricultural matrix, which differs from the larger areas of dense contiguous forest documented in the core of the species' range. Despite apparent limitations, this forest-dependent species is still finding roost locations, choosing the tallest trees in the densest patches available. Maintaining these resources and conditions is important for conservation of this endangered bat, especially as even-aged stands of cottonwoods mature. Improving our understanding of habitat selection of northern myotis at the periphery and core of their range is essential to support this endangered species in the face of environmental changes.