Roosting behaviour of silver-haired bats (Lasionycteris noctivagans) and big brown bats (Eptesicus fuscus) in northern Oregon

I used telemetry to locate maternity roost sites of four Eptesicus fuscus and five Lasionycteris noctivagans in northern Oregon, and I measured characteristics of the roost tree, roost site itself, and surrounding habitat. I also recorded the frequency and distance of roost shifts and the size of some maternity colonies. Both species used large live and dead trees with the diameter of the trees used by E. fuscus being significantly larger than those used by L. noctivagans. Roosts sites were high, uncluttered, and faced no particular direction. None of these features differed significantly between the two species. Trees used by E. fuscus were in significantly more open forest on flat terrain than those used by L. noctivagans. E. fuscus tended to have larger maternity colonies than L. noctivagans. Bats of both species changed roosts trees frequently. E. fuscus moved farther between trees than did L. noctivagans, most of which remained in the same drainage. Because of roost-tree lability and the need for large trees as maternity roosts, it is important that forest planners retain large trees when laying out salvage and green timber sales.