Introduction

The present paper is concerned with the recruitment rate of young common brushtail possums Trichosurus vulpecula into a population, how this relates to the age and physical condition of the female and, ultimately, to annual variations in density, climate and food-supply. Live-trapping data for the decade 1966-75 are the basis for this analysis. Previous information on the breeding biology of possums in the Orongorongo Valley is given by Kean (1959, 1967, 1971, 1975, unpublished), and by Crawley (1970, 1973) who initiated aspects of the present study over 1966-68. The investigation has continued since 1975 as part of a long-term study of possums by the Ecology Division of D.S.I.R.