Autumnal body mass reduction in Antechinus swainsonii (Dasyuridae) in the Snowy Mountains.

Abstract

Autumnal body mass reduction in a seasonally snow-covered environment is reported for Antechinus swainsonii (Marsupialia: Dasyuridae), thus extending the phylogenetic spectrum in which this phenomenon is known. Above 1600 m altitude the average mass of individual A. swainsonii falls from 48.6 g to 42.6 g (a 12.3% loss) from April to May. The difference in mass results from a reduction in lean mass rather than a metabolisation of fat reserves. In A. swainsonii, the need to increase body mass in late summer only to lose it in autumn prior to a winter beneath the snow seems superfluous. However, the higher mass may be necessary to survive the harsher microclimate in autumn before conditions ameliorate beneath the snow cover. Survival from April to May is higher in heavier animals (that do lose mass in autumn) than lighter animals (with mass in April equal to that of animals after loss of body mass). These lighter animals disappear from the population in autumn. With snow cover in place, A. swainsonii is able to increase mass in winter.