Abstract
Most eastern North American Myotis roost in forests during summer, with species forming maternity populations, or colonies, in cavities or crevices or beneath the bark of trees. In winter, these bats hibernate in caves and are experiencing overwinter mortalities due to infection from the fungus Pseudogymnoascus destructans, which causes white-nose syndrome (WNS). Population recovery of WNS-affected species is constrained by the ability of survivors to locate habitats suitable for rearing pups in summer. Forests in eastern North America have been severely altered by deforestation, land-use change, fragmentation and inadvertent introduction of exotic insect pests, resulting in shifts in tree distributions and loss of large-diameter canopy-dominant trees. This paper explores patterns in use of tree roosts by species of Myotis across Canada and the United States using meta-data from published sources. Myotis in western Canada, the Northwest, and Southwest selected the largest diameter roost trees and also supported the largest maximum exit counts. Myotis lucifugus, M. septentrionalis and M. sodalis, three species that inhabit eastern forests and which are currently experiencing region-wide mortalities because of WNS, selected roosts with the smallest average diameters. Recovery efforts for bark- and cavity-roosting Myotis in eastern North American forests could benefit from management that provides for large-diameter trees that offer more temporally-stable structures for roosting during the summer maternity season.
Highlights
Alterations to forested landscapes across eastern North America from shifting land use practices, fire suppression, and inadvertent introduction of exotic forest pests have led to reduced forest land cover, younger stand ages, and changes in the composition of canopy-dominant trees
Tree roosts of Myotis exhibited a decreasing trend for height of roost trees from west to east across the United States (F7,54 = 5.39, p < 0.0001); data for Canadian populations were reversed with the tallest roost trees recorded in eastern Canada (Figure 3)
Average roost-tree diameter differed among Myotis with western species occupying the largest roosts on average, and eastern species selecting the smallest diameter roosts, especially M. sodalis, eastern and Midwestern populations of M. septentrionalis, and populations of the eastern subspecies of M. lucifugus lucifugus
Summary
Alterations to forested landscapes across eastern North America from shifting land use practices, fire suppression, and inadvertent introduction of exotic forest pests have led to reduced forest land cover, younger stand ages, and changes in the composition of canopy-dominant trees. Eastern oak (Quercus) forests have seen a widespread increase in shade-intolerant hardwoods and a decline in shade-intolerant oaks resulting from decades of fire exclusion [3]: an ecological response termed “mesophication” [4]. These forests are further threatened by outbreaks of gypsy moths (Lymatria dispar), which cause mortality of both overstory and young trees in oak species [5]. Canopy-dominant tree species in eastern North America have experienced mortalities and declines due to introduced forest pests including Canadian hemlock (Tsuga canadensis), American beech (Fagus grandifolia), ash (Fraxinus spp.), and American chestnut (Castanea dentata) [6]. Shifts away from historically available tree species and canopy structures are likely to be accompanied by changes in behavior of bark- and cavity-roosting bats, in selecting roosting and maternity habitats during summer months
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