Abstract

"Aspects on the ecology of insectivorous bats forest-dwelling bats in the western slopes of the Australian alps"

This study investigated the species composition, abundance and ecology of forest dwelling bats in the western slopes of the Australian alps. Field work was conducted from December 1995 to February 1997. Investigations into currently used methods in bat surveys identified problems with bat call identification, caused mainly by the lack of reference calls available.

Mathematical properties of bat calls were examined for their usefulness in distinguishing between species. Variability of echolocation calls caused misclassification of some bats, although most of the species could be identified by their calls. Modern computer applications have the potential to automate bat call identification, provided local reference calls are available.

The number of bat calls recorded per unit time were found to be not correlated to the number of captures in the same area and time period. This result implies that one method cannot replace the other. Bat surveys should employ both trapping and echolocation call detection techniques to appropriately identify all bat species in an area.

The study area potentially supported 17 bat species. This study identified 14. One of the undetected species (Myotis macropus) was detected in an earlier survey in the study area. The two remaining undetected species are unlikely to occur in significant numbers in the study area due to their general scarcity (Nyctophilus timoriensis) or current distribution (Scotorepens balstoni). The species combination in the western slopes of the Australian alps is typical of a community in a transition zone consisting of open forest and woodland.

Variability in the size of bats conformed to the ecological principle known as Bergmann’s rule: body size and activity of larger species increased with altitude.

Regional variability in bat echolocation calls was observed for Chalinolobus gouldii, C. morio, Falsistrellus tasmaniensis, Nyctophilus geoffroyi, Vespadelus darlingtoni and V. vulturnus. This emphasises the point that identification of bats by their calls may be only reliable when using locally recorded references calls. Call frequency increased with the body size of the bat species.

The recapture rate of banded bats (7%) did not allow accurate population estimates to be determined. One of the findings of this investigation is that marking of bats can only be justified when a study is specifically designed to estimate population size. Bats were found to have unequal sex ratios. Sex ratios changed between species, sites and between lactation and non-lactation periods.

The foraging activity of different bat species related in different ways to the structural parameters of the vegetation, generally reflecting bat echolocation ability and manoeuvrability. Bats tended to forage in more open environments, thereby avoiding clutter in the canopy-subcanopy level.

The study identified differences in size and type of insect remains in the pellets of F. tasmaniensis, V. darlingtoni and V. vulturnus. This can be interpreted as an indication of resource partitioning most likely induced by the size differences among the species. This is further supported by the direct comparison of the diets of the syntopic species V. darlingtoni and F. tasmaniensis.

Roosting habitat preferences were investigated for V. darlingtoni and F. tasmaniensis. Both species had a preference for older and larger roost trees. V. darlingtoni preferred older smooth-barked trees and F. tasmaniensis selected roost areas with lower tree density and higher density of older, hollow-bearing trees. The results of this investigation led to detailed suggestions for the mitigation of forestry impacts.

An investigation into the potential habitats of F. tasmaniensis in north-eastern Victoria revealed that in future it may become threatened, because the habitat distribution could be reduced to one third of the current state, and roost site availability could be decreased by half. Detailed suggestions for identifying forest habitats needed for the conservation of F. tasmaniensis are offered.