Characterizing summer roosts of male little brown myotis (Myotis lucifugus) in lodgepole pine-dominated forests

Abstract

Although bat roosts have been well-studied in the eastern United States, we know less about roosts in the west. Western bats may make use of trees and snags, as in the eastern US, but the Rocky Mountains provide more exposed rock, which could contribute to western bat species using different roosting features. Additionally, roost studies often focus on maternity colonies, and information on roosts used by male bats is limited. Given that roosting sites may be limiting, we aimed to quantify structural features of roosts used by male little brown myotis (Myotis lucifugus) in forests dominated by lodgepole pine (Pinus contorta) during the summer and determine whether bats are selecting roosts with particular features disproportionately to what is available on the landscape. We mist-netted for bats during the summers of 2017 and 2018 and attached transmitters to 34 male little brown myotis. We located at least 1 roost for 20 individuals (average = 2.85 roosts/bat, range = 1-6). Although snags were available, most bats roosted in rock features (86% in rocks, 14% in snags); rock roosts were mainly in crevices with vertical orientations (85%) instead of rock cavities (15%). Male bats were more likely to select roosts with less canopy closure (mean for used locations = 14.1%, SE = 2.3) that were closer to water (1063.1 m, SE = 136.2). They also selected roosts with more overall rock cover (77%, SE = 3), wider entrances (3.1 cm, SE = 0.3), and access to a skyward-facing crevice, creating warmer microclimates. Our work indicates that rock features provide essential summer habitat for male little brown myotis and that lodgepole pine in this landscape may not provide appropriate roosting features. Understanding how other bat species may be using rock features, during summer and other seasons, remains a sizeable information gap. Learning more about hibernacula is of great importance due to the spread of white-nose syndrome and rock features may be essential autumn transitional roosts and winter hibernacula at higher elevations. Roosts that provide variation in microclimate, including the potential for passive warming, could be very beneficial for bats recovering from white-nose syndrome.