Day roost selection by female little forest bats (Vespadelus vulturnus) within remnant woodland on Phillip Island, Victoria

Abstract

The day roosting behaviour of the little forest bat (Vespadelus vulturnus), Australia’s smallest bat, was investigated in the context of the planned removal of dead timber within managed woodlands on Phillip Island, Victoria. Between August 1999 and March 2000, 14 female little forest bats were fitted with VHF microtransmitters and tracked to a total of 16 roost trees. All roosts were located in dead timber, 11 in severely decayed remains of eucalypt trees, and five in dead sections of live trees. Roost trees were compared with randomly chosen trees from within the available habitat, for a range of tree characteristics. Female little forest bats selected roosts in trees with dead timber offering many hollows and reduced canopy cover. Furthermore, roost trees were located in areas (0.1-ha plots) with higher densities of these types of trees than in the available habitat. However, there was no difference in the height or diameter of roost trees or roost plots compared with available habitat. Emergence time from roosts was strongly associated with civil twilight (when the centre of the sun is 6° below an ideal horizon), and the number of bats exiting a single roost tree ranged from 1 to 120 (median = 20). Dead trees provide critical roosting habitat and we recommend retention of dead standing trees for conserving little forest bat roosts in managed woodlands.