A field study of Pseudocheirus occidentalis (Marsupialia : Petauridae) II. Population studies

Abstract

Field studies of the rare and endangered western ringtail possum (Pseudocheirus occidentalis) were undertaken at five main sites in south-western Australia. Population studies employing capture-markrelease and telemetry methods were concentrated at Abba River and Locke Estate, near Busselton, and supplementary telemetry records were obtained for three females at Yendicup, Perup, near Manjimup. The location of dreys and sightings were mapped at Geographe Bay (near Busselton) and Emu Point (Albany). Mature adults of both sexes weighed about 1000 g and attained maturity at 830-900 g. Young were estimated to spend about 104 days in the pouch and emerge at 130-150 g. Lactation ceased when young weighed 550-650 g. Most births were of single young, but at Locke 16.7% of females with pouch young carried twins. In the Busselton area some births occurred in all months, but there were few between December and March. Most births occurred during April-July, but a secondary peak occurred during September-November, especially at Locke. At Locke 69% of animals were females and this ratio was similar in all age classes, but at Abba the sex ratio was parity. At Locke hollows were rare and animals usually rested in dreys; at Abba hollows in Eucalyptus gomphocephala were the usual rest sites and dreys were rare, occurred only near the watercourse and were used only by males; at Yendicup no dreys were observed and hollows in eucalypts were the usual rest sites. Animals used 2-7 rest sites each. Home ranges of females at Yendicup averaged about 2.5 ha; in the Busselton area home ranges averaged less than 1 ha. Less than 1% of both day and night sightings were of animals at ground level. Plots of the location of dreys and sightings at three sites showed that possums were not evenly dispersed, and at two sites there were areas of apparently suitable habitat that were rarely used. Density was estimated for four sites: Abba River 3.7-4.3 ha-1, Locke Estate 2.4-4.5 ha-1, Geographe Bay 0.3-0.6 ha-1 and Emu Point 0.1-0.4 ha-1. Evidence of predation by foxes was found at Abba, Locke and Geographe Bay. Microscopic inspection of faecal pellets showed that, where Agonis flexuosa grew, its leaves accounted for 79-100% of diet. Small amounts of several other plants were also taken. At Perup A. flexuosa was absent and the diet consisted predominantly of leaves of the two common eucalypts (Eucalyptus calophylla and E. marginata).