Selection of roosting and foraging habitat by bats in different-aged aspen mixedwood stands

In aspen mixedwood forests, habitats that provide roosting and foraging sites for bats likely occur in old stands and thus may be threatened by logging. To determine if bats prefer certain ages of aspen mixedwood forest and to help predict the impacts of logging on bats, we used handheld bat detectors and mistnets to compare the relative use and foraging activity by bats in young, mature, and old stands in northern Alberta in 1993 and 1994. We assessed roost-site selection by tracking radio-tagged female little brown bats (Myotis lucifugus) and silver-haired bats (Lasionycteris noctivagans) to roost trees, which we measured and compared to a random sample of potential wildlife trees. Occurrence of all bats combined was significantly higher in old stands than in young stands in 1993. In 1994, occurrence and activity were higher in old stands than in either young or mature stands. Myotis spp. activity was also higher in old stands. All 27 roost trees were in old stands. Bats preferred tall (mean: 22.0 m), dying, or newly dead Populus spp. with heart rot and low leaf cover. Such trees were scarce in young and mature stands. Tree-roosting colonies were small (4–63 bats) and transient; most tagged bats roosted in more than one tree. Bats likely select trees large enough to house colonies and provide suitable temperatures, and these trees are most common in old stands. Roost preference may explain observed activity patterns. As more roost trees are harvested, we predict that bat abundance will decrease in remnant patches of fragmented stands. To sustain bat populations in these forests, old stands must be retained and roost sites preserved by managing the forest at the stand or landscape level