Effects of habitat fragmentation on the demography, movements and social organisation of the eastern pygmy-possum (Cercartetus nanus) in northern New South Wales

A population of eastern pygmy-possums (Cercartetus nanus) was studied in northern New South Wales for almost 3 years. A total of 98 pygmy-possums was captured, of which 52 were captured only once. The sex ratio of the population did not differ significantly from parity. Mid-way through the study, 1.4 ha of the 4.0-ha study site was cleared. Pre-clearing capture rates in nest boxes averaged 33.5 +/- 5.8 captures per 100 box checks per month, and the population was estimated by three methods to be at least 15-20 animals. There was no significant difference in body mass between adult males (23.7 +/- 6.3 g) and adult females (27.1 +/- 7.7 g). Males had significantly larger short-term home ranges (0.35 +/- 0.14 ha) than females (0.14 +/- 0.06 ha) and tended to move over greater distances each night. Breeding occurred from summer to early winter, and juveniles and sub-adults entered the population in autumn and winter. The mean number of pouch young was 3.9. The most likely minimum size at which juveniles left their mother was 9-11 g. Adult body mass and condition were highly variable over time, and did not appear to be related to either the breeding season or Banksia flowering. Fourteen pygmy-possums were found torpid during the study. Population troughs occurred in late winter and spring and were associated with low survival and/or seasonal migration, possibly linked to the cessation of Banksia flowering in July and the lack of alternative food sources at this time and/or increased use of nest boxes by Antechinus stuartii during late winter. Post-clearing, capture rates fell to 7.8 +/- 1.6 captures per 100 box checks per month, the estimated population size fell to 5-8 animals, and there was an almost total lack of juvenile/sub-adult recruitment into the population. The results support concerns that the long-term survival of the eastern pygmy-possum in New South Wales is threatened by continued land clearing throughout much of its present range.