Demography of Westland Petrels (<i>Procellaria westlandica</i>), 1995–2003

Abstract

We studied the Westland Petrel (Procellaria westlandica) over 9 years to estimate demographic rates and examine the possible influence of fisheries by-catch and nest predators on the population. Mean annual survival rates of breeders and skipped-breeders averaged 0.965 (s.e. = 0.038) and 0.726 (s.e. = 0.173) respectively. Mean fledging success was 0.62 fledglings per egg laid (s.e. = 0.04, n = 34 nests). The birds studied showed no evidence of elevated mortality at either the adult or nestling stages, which might indicate low fisheries by-catch mortality or few predation threats to population stability or both. With apparent survival rates of breeders being near probability of 1, attempts to manage threats to the population, over and above current levels of management, can do little to elevate these survival rates. However, some management actions such as ameliorating habitat destruction or depredation could benefit non-breeding birds, as well as working to keep survival rates in breeding birds high.