Day-Roosting Habitat of Female Long-Legged Myotis in Ponderosa Pine Forests

Abstract

We studied use of day roosts by adult, female long-legged myotis (Myotis volans) in 4 watersheds dominated by ponderosa pine (Pinus ponderosa) forest east of the Cascade Crest in Washington and Oregon, USA, 2001–2003. To investigate maternity habitat in managed, xeric forests we radiotracked 87 bats to 195 snag roosts and 34 rock crevices totaling 842 roost-days. Bats changed roosts every 2.7 ± 0.1 (SE) days and averaged 3.6 ± 0.3 roosts per bat. Roosts were 2.0 ± 0.1 km from capture sites, and bats moved 1.4 ± 0.1 km between successive roosts. Six bats (6.9%) day-roosted in rock crevices exclusively, 9 bats (10.3%) used snags and rock crevices, and the remaining bats (82.8%) day-roosted in snags exclusively. Most snag roosts were thick-bark ponderosa pine (n = 103; 52.8%) or thin-bark grand fir (Abies grandis) and white fir (Abies concolor) (n = 74; 37.9%). Over half of all snag roosts (n = 101; 52%) were used by solitary bats; 28 snag roosts (14%) housed >50 bats (large-flyout roosts). Ninety-three percent of large-flyout roosts were in ponderosa pine snags. Large-flyout roosts were larger, taller, and retained more exfoliating bark and total bark than small-flyout roosts (P < 0.05), and small-flyout roosts were larger, taller, and retained more exfoliating bark and total bark than random snags (P < 0.05). Snag roosts were closer to other snags, located in areas of greater snag density, with greater snag basal area and greater basal area of snags >25 cm diameter, and were lower in elevation than random snags (P < 0.05). Pregnant bats divided roost-days almost evenly between thick and thin-bark snags (52.7 vs. 47.3%), whereas lactating bats roosted in thick-bark snags more often than they did in thin-bark snags (80.3 vs. 19.7%, P < 0.0001). Pregnant bats roosted in both upslope and riparian zones (57.5 vs. 42.5%), but lactating bats spent more days roosting upslope than in riparian zones (73.1 vs. 26.9%, P < 0.0001). These findings suggest that reproductive female long-legged bats choose roosts relative to their changing physiological needs. We recommend that management of forests for sustaining habitat of female long-legged myotis in the east Cascades ensure the continued availability of both thick- and thin-bark snags in early stages of decay, in both riparian and upslope positions.