ECOLOGY OF NATURAL HIBERNATION IN THE MARSUPIAL MOUNTAIN PYGMY-POSSUM(BURRAMYS PARVUS)

The hibernating marsupial mountain pygmy-possum (Burramys parvus, 40 g ) has to raise its slow-growing offspring during a short alpine summer . Only females provide parental care, while after mating males emigrat e to marginal habitats often at lower altitudes which can sustain only low possum densities. We predicted that the hibernation strategies in mountain pygmy-possums are distinct from those of similar-sized place ntal hibernators, because of the developmental constraints in marsupia ls and because hibernation differs between the sexes. Using temperatur e-sensitive radio transmitters, we studied the hibernation patterns of free-living male and female mountain pygmy-possums living in a north- and a south-facing boulder field (Kosciusko National Park) for two con secutive winters. Individual possums commenced hibernation several mon ths before the snow season. As in other hibernators, torpor in the mou ntain pygmy-possum was interrupted by periodic arousals which occurred most often during the late afternoon. Torpor bouts initially lasted a few days when the hibernacula temperature (T-hib) ranged from 4 to 7 degrees C. As the hibernation season progressed, torpor bouts became l onger and possum body temperatures (Tb) approached 2 degrees C. The T( b)s Of females were significantly lower and torpor bouts were longer i n the second half of the hibernation season than in males. Between tor por bouts, both sexes were often active and left hibernacula for perio ds of up to 5 days. Especially during the first months of the hibernat ion season, possums also frequently changed hibernacula sites probably in an attempt to select a site with a more suitable microclimate. Eme rgence from hibernation was closely coupled with the disappearance of snow from the possum habitat (September 1995, October 1996) and the li mited fat stores probably dictate an opportunistic spring emergence. H owever, in 1995, spring was early and males emerged significantly earl ier than females. In 1996, when snow melt was delayed, this difference vanished. Testes are regressed in males during hibernation and the ti me needed for testes growth and spermatogenesis favours an earlier eme rgence for males which was probably achieved by their preference for t he more sun exposed north-facing boulder field. A sexual dimorphism in hibernation strategies and spring emergence therefore enables mountai n pygmy-possums to cope with their harsh alpine environment.