In possum populations studied in the Orongorongo Valley, near Wellington over 1966-75, 99% births occurred in late autumn or early winter (April-June); spring births were rare. Yearling females rarely bred and failed to rear pouch-young. Overall about 60% two-year-olds and 85% older females bred; both age groups reared just over half their pouch-young. Annual recruitment of young barely compensated for mortality of older possums. There was variation in female breeding success between two areas of lowland forest and in both the productivity was low compared with populations studied elsewhere.

In the main study area there was marked annual variation in breeding productivity correlated with changes in female body weight; in years of higher mean weight of females births tended to be earlier, more females bred and more of their young survived. This probably reflects annual variations in weather, food supply and possum density, although the interplay of the factors affecting the productivity and numbers of the possum population is not fully understood.