Winter roosting ecology of silver-haired bats (Lasionycteris noctivagans) in southern British Columbia

Many animals spend a considerable amount of time within a shelter, and shelter availability can influence the distribution, abundance, and diversity of animal populations. Shelters used during winter, when ambient temperatures are low (< 0°C), must provide animals with adequate protection to survive through months of adverse conditions. For bats, shelters (roosts) used during winter must also provide microclimates that support energetic requirements for hibernation. Silver-haired bats (Lasionycteris noctivagans) are a tree-roosting species that are migratory throughout much of their range. In parts of northwestern North America, however, they may hibernate locally. Hibernation sites (hibernacula) in regions where winter temperatures are below freezing are typically caves, underground mines, or rock crevice features, as these protect bats from cold temperatures and provide a humid environment that prevents dehydration. In a forested area near Beasley in southern British Columbia, silver-haired bats use an abandoned mine, rock crevices, and trees as roosts during winter. The use of trees as roosts during winter in cold regions (average temperatures < 0°C) is poorly understood. I sought to investigate the winter ecology of tree-roosting silver-haired bats in southern British Columbia. In Chapter 2, I described the characteristics of trees used as hibernacula by silver-haired bats. I hypothesize that bats select winter roost trees non-randomly, and differently across seasons. In Chapter 3, I investigated microclimates and torpor patterns inside silver-haired bat mine, tree, and rock crevice hibernacula. I hypothesize that microclimates vary among winter roost types, and because of these differences, torpor, arousal and movement patterns will differ among tree, rock crevice and mine winter roosts. A majority (66.7%, n = 22) of silver-haired bats used trees as winter roosts during the study. Winter tree roosts were selected non-randomly, and compared to summer roosts, bats used features that provided insulation, such as, cavities in large-diameter, low-decay trees in areas of low canopy closure. Winter trees roosts were colder but more humid compared to the mine and rock crevice roosts. Bats switched among roosts throughout winter depending on ambient conditions but did not alter torpor patterns among roost types. Bats typically used humid roosts (trees) on drier days, and less humid roosts (mine) on more humid days. Further, bats used the well-insulated mine on colder days, and poorly insulated trees and rock crevice roosts on warmer days. Despite this, bats showed more tolerance for colder roost temperatures than expected, remaining in trees during periods of cold (-9°C) temperatures. I conclude that there may be a trade-off between roost humidity and temperature, with bats using multiple hibernacula to optimize energetic benefits in the context of ambient conditions. Trees are an important part of silver-haired bat winter ecology. The use of trees as hibernacula needs to be better understood to inform forest management decisions that better support silver-haired bat conservation by protecting important winter roosts

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