Physical and microclimate characteristics of Nyctophilus gouldi and Vespadelus vulturnus maternity-roost cavities

Context. Tree cavities suitable to rear young are a key resource in managed landscapes to support viable populations of tree cavity-roosting bats. Little is known about the selection of cavities for maternity roosts, presumably because of the difficulty in accessing such roosts. Aims. Our study investigated physical and microclimate characteristics of maternity roosts of two species, namely, Gould's long-eared bat (Nyctophilus gouldi) and little forest bat (Vespadelus vulturnus). Methods. Maternity-roost cavities were identified in a timber-production landscape in south-eastern Australia. Roost trees (V. vulturnus n= 5; N. gouldi n = 9) and a subsample of available cavity-bearing trees (n = 16) were climbed to obtain cavity characteristics. Key results. Vespadelus vulturnus used tree hollows exclusively, whereas N. gouldi used both tree hollows (n= 7) and thick loose bark (n = 2). No significant difference in roost-cavity characteristics was detected between the species. However, V. vulturnus selected significantly narrower cavity entrances (mean: 16 +/- 3 mm) than those of the available cavities. Temperature did not differ between maternity roosts and available cavities when investigated after the maternity season. However, a V. vulturnus maternity roost occupied for 33 consecutive days was warmer than mean roost and available cavities, suggesting that long-term roost use may be influenced by the thermal property of a cavity. Conclusions. Our study has provided the first detailed tree-cavity description of maternity roosts of N. gouldi and V. vulturnus. The nightly roost switching and the large variation of tree-cavity characteristics used by N. gouldi suggest that this species requires a high density of non-specific tree cavities that are large enough for colony formation, whereas preferred roost cavities for V. vulturnus are likely to be hollows comprising narrow entrances that facilitate long-term use.