Seasonal changes in activity and weight of Minipterus schreibersi blepotis (Chiroptera) in north-eastern NSW.

Abstract

In north-eastern New South Wales M. s. blepotis occupies caves and mines in three distinct climatic regions: the subtropical coastal belt, the tablelands (cold winters), and the inland slopes (intermediate winter temperatures). Conspicuous seasonal differences in level of daytime activity are evident at roosts. In the summer the bats typically disperse rapidly from clusters, but during the winter they are relatively sluggish and may remain clustered for more than half an hour after disturbance. Selection of different roosting sites and a change in the roosting attitude of the bats accompanies the changes in level of activity. During the winter, feeding activity is considerably reduced except perhaps for colonies in the warmest of the coastal areas. Conspicuous regional differences in seasonal weight changes occur so that bats from the tablelands increase in weight before winter but coastal bats do not. "Prehibernation" weights of bats from the inland slopes are intermediate between those from coastal and tableland areas. For the bats from the tablelands, about 22% of prehibernation weight is lost during the winter. On the assumption that level of activity reflects body temperature, it is suggested that summer M. s. blepotis characteristically regulate their body temperature but that wintering individuals are essentially poikilothermic when roosting. It is concluded that the capacity to lay down fat reserves before winter, and to select appropriate habitats and temperatures, combined with the seasonal change from a maintained high summer metabolism to a poikilothermous winter pattern, are significant factors in the adaptation of M. s. blepotis to the winter conditions of north-eastern New South Wales.