Conservation of Bats in Managed Forests: Use of Roosts by Lasionycteris noctivagans

Abstract

In large regions of the Pacific Northwest of the United States, harvest of forests has converted old-growth coniferous forests into a mosaic of young patches (<90 years old) of differing size and age. We examined the consequences of these changes on the roosting habits of the silver-haired bat, Lasionycteris noctivagans, which preferentially uses older forests in other parts of its range in the Pacific Northwest. Bats were captured using mist nets and harp traps at streams, ponds, and road sites in 1992 and 1993. L. noctivagans was captured only over water. Fifteen of 30 L. noctivagans captured were equipped with radio-transmitters. A total of 15 roost sites used by 13 individuals was found. All roosts were <3.5 km from the initial capture site and were in dead or dying trees with exfoliating bark, extensive vertical cracks, or cavities. Fourteen roosts were in trees with diameter at breast height >30 cm. Height of roost trees ranged from 6.9 to 61.5 m, and estimated height of roosts of bats ranged from 6.1 to 15.2 m. Roost trees were significantly taller than neighboring trees, which may facilitate the location of roosts by bats. Analysis of a 15-m radius plot around each roost tree revealed that roost sites had significantly less closure of over-story canopy, less understory, and shorter understory vegetation than comparable random plots. Reduced overstory canopy and understory vegetation provide a less-cluttered environment for flight of bats, which may be particularly important for newly volant young. Recruitment and retention of snags and the maintenance of structural complexity in forest patches in upland as well as riparian areas are important for the conservation of species of bats in managed forests.