A FIELD-STUDY OF PSEUDOCHEIRUS-OCCIDENTALIS (MARSUPIALIA, PETAURIDAE).1. DISTRIBUTION AND HABITAT

Surveys aimed at determining the distribution and habitat of the rare and endangered western ringtail possum (Pseudocheirus occidentalis) we re undertaken in south-western Australia during 1990-92. Surveys relie d on sightings of animals, or their characteristic faecal pellets or d reys. Habitat descriptions were collected in areas occupied by P. occi dentalis to describe the vegetation and topography. Additional informa tion about habitat was collected at subsets of sites to reflect leaf n utrient levels (nitrogen, phosphorus and potassium) of the major food plants, and to reflect the relative senescence of vegetation communiti es, and their fire and fox-baiting history. The species has a patchy o ccurrence from the Collie River to Two Peoples Bay, occurring most com monly in coastal or near-coastal forest that includes Agonis flexuosa as a major component. The most inland population occurs at Perup and t his is the only known population living in forest without A. flexuosa. Local extinction has been extensive in the inland and northern parts of the original range (as it was known about 1900) and local decline h as been patchy and occurred in most decades (1900-89) in different par ts of the original range. Analysis of a matrix of relative abundance a nd habitat variables identified two habitat parameters associated with higher abundance of P. occidentalis: higher levels of nitrogen in fol iage of the major food plant and a higher degree of canopy continuity. Hollow abundance was also implicated as a covariate of relative abund ance. Assessment of levels of nitrogen, potassium and phosphorus in A. flexuosa leaves indicated that occupied sites tended to have relative ly high nutrient levels. The pattern of decline and persistence of pop ulations in different habitats is discussed with respect to environmen tal factors considered to have changed over the last century.