Factors influencing the selection of roost cavities by a temperate rainforest bat (Vespertilionidae : Chalinolobus tuberculatus) in New Zealand

The selection of roost cavities by the threatened New Zealand long-tailed b at Chalinolobus tuberculatus was examined in unmodified temperate southern beech Nothofagus rainforest in Fiordland, New Zealand. We radio-tracked 73 bats during spring-autumn of 1993-1997 to 155 day roosts, all of which were in trees. One hundred and forty-nine roosts were in cavities: 84 in live t runks, 33 in dead trunks, 32 in large branches (seven in dead branches, 25 in live); and the remaining six (occupied by solitary bats) were beneath lo ose bark. We compared characteristics of the 84 roost cavities in live trun ks with 57 random available cavities also in live trunks. Cavities used by C. tuberculatus were not a random subset of available cavities. In comparis on to available cavities, bat roosts were all located in knot hole cavities , were high from the ground, and had little surrounding vegetation. All roo sts were dry inside. Bats used a higher proportion of cavities which had me dium sized entrances and internal cavities, and thicker cavity walls. A log istic regression model incorporating nine cavity variables classified roost and available cavities correctly 97% and 91% of the time, respectively. Di stance to the nearest vegetation, cavity condition (wet or dry inside), hei ght from the ground, and to a lesser extent internal cavity height, explain ed significant proportions of the variation between roost and available cav ities. Bats changed roost sites virtually every day and it appeared that su itable cavities were abundant in the unlogged forests of the study area. It is unlikely that modified forests and forests managed for timber productio n contain such a large pool of potential roosting cavities.