A live-trapping of Australian brush-tailed possums, Trichosurus vulpecula (Kerr), in the Orongorongo Valley, Wellington, New Zealand

Abstract

A live-trapping study of a population of Australian brush-tailed possums, Trichosurus vulpecula (Kerr), in indigenous forest of the Orongorongo Valley, Wellington, N.Z., was carried out from March 1966 to November 1968. In 14 ha of podocarp-mixed broadleaf forest, 301 possums (150; 151) were individually marked and repeatedly captured in a series of trapping periods. The population comprised residents and transients of both sexes with sub- adults forming the bulk of the latter, particularly in spring. The estimated population density varied from 10.6 per ha in November 1966 to 6.4 per ha in August 1968. There was one well-defined season of births each autumn and a few births in winter. On average, 73% (67-92%) of mature females produced pouch young each year. Females resident throughout the study had the highest breeding success (79%). Achievement of sexual maturity was delayed; no females bred until they were 2 yr old, and some not even at 3 yr. Losses occurred at all stages of the life history and averaged 62% between the pouch young and subadult stages; thus only 28 subadults per 100 females were recruited. Adult losses averaged 26% per annum. Adult males (mean weight 2.46 kg) were heavier than adult females (2.33 kg). Weights varied seasonally, with males heaviest in summer and lightest in spring, and females heaviest in winter and lightest in summer. Possums of both sexes were rather sedentary, with males (95% of captures within 115 m of the initial capture site) being less so than females (95 % of captures within 90 m of the initial capture site). More than half of the captures (55% for males, 62% for females) were made within 30 m of the site of initial capture. Males moved farther in autumn and summer than in other seasons, while females did so in autumn and winter. Subadults were apparently more sedentary than adults. Home ranges of adult males (mean 0.81 ha) were significantly larger than those of adult females (0.46 ha). Considerable overlapping of the ranges of both sexes occurred, and territorial behaviour was not conspicuous. The dispersion of the population remained the same throughout the study although the component individuals changed. The results of the present study are compared with those of similar studies in New Zealand and Australia, and the dynamics of the Orongorongo Valley possum population are discussed with reference to variable rates of reproduction and mortality.