MODELING SURVIVAL AND CAPTURE PROBABILITIES OF THE MOUNTAIN BRUSHTAILPOSSUM (TRICHOSURUS-CANINUS) IN THE FORESTS OF SOUTH-EASTERN AUSTRALIA USING TRAP-RECAPTURE DATA

The results are described of a capture-recapture study of the Australi an arboreal marsupial, the mountain brushtail possum (Trichosurus cani nus Ogilby). Adult, subadult and juvenile T. caninus were captured dur ing 11 trapping periods and at 70 different trap placement sites betwe en June 1992 and November 1995 in a 40 ha area of mountain ash (Eucaly ptus regnans F. Muell.) forest in the central highlands of Victoria, s outh-eastern Australia. A total of 80 (37 male and 43 female) T. canin us were captured, comprising 45 adults, 14 subadults and 21 juveniles when first trapped. This gave a total of 333 captures of T. caninus fr om approximately 4600 trap nights. The Jolly-Seber-Cormack approach wa s employed to model the frequency of recapture as simple product funct ions of the survival and capture probabilities for each inter-trapping interval. Using this method, we explored the relationships between su rvival and capture probabilities of T. caninus and a range of potentia l explanatory variables including sex, age class, time, and trap locat ion. The results of our analyses indicated that there was a high proba bility of recapture of T. caninus-P=0,80 (0.03 se-with females signifi cantly (P<0.05) more likely to be caught than males. There was spatial heterogeneity across our study site in the probability of recapture o f T. caninus, and animals inhabiting areas of old growth were more lik ely to be retrapped than animals in younger forest where potential nes t sites within large standing dead trees with hollows are decaying rap idly and are at high risk of collapse. There were no significant diffe rences between the survival rates of different sexes or age classes, a nd the monthly value for the probability of persistence calculated for T. caninus was 97.7% (0.48%). Our study demonstrated that T. caninus is long-lived with high levels of survival among individuals of all ag e classes once young animals have emerged from the pouch. Animals have relatively high site affinity and are readily recaptured, often at ex actly the same place, or very close to, where they were first caught. Some juveniles have taken up permanent residence in the natal territor y, which may result in opportunities to mate with close relatives.