Altitudinal and Seasonal Differences in the Diets of Antechinus-Swainsonii and Antechinus-Stuartii (Marsupialia, Dasyuridae) in Relation to the Availability of Prey in the Snowy Mountains

Abstract

The diets of Antechinus stuartii and A. swainsonii and the availability of their prey were studied in the Snowy Mountains in areas subjected to a winter cover of snow. Active prey were found to be less common in winter than summer and less common at higher than lower altitudes. The prey taken were more likely to reflect availability (as measured either by pitfall traps or litter samples) where prey was scarce. The diet varied between years but within years was more variable for A. stuartii than for A. swainsonii, possibly because A. stuartii was able to feed in trees in summer but not in winter, whereas A. swainsonii foraged only on the ground in all seasons. Antechinus stuartii and A. swainsonii fed on different types of prey at low subalpine altitudes (1600 m), where they foraged in different microhabitats; this difference was also reflected in the sizes of prey consumed. At high subalpine altitudes (1850 m), A. stuartii and A. swainsonii fed on both the same type and the same size of prey, indicating that the two species did not select different prey sizes but that prey size was determined by the size of food available to each species. Predation on a particular group by A. swainsonii in summer was more likely if that prey group was also available in winter. This suggests that by improving its skills at finding and catching these prey, A. swainsonii was better fitted for survival through the winter. This may help explain the greater abundance of A. swainsonii and the decline in numbers of A. stuartii almost to local extinction in snow-covered areas.