Variation in productivity of Grey-faced Petrels (Pterodroma gouldi) with local burrow density and breeding island

Abstract

For long-lived birds, estimates of productivity can be effective indicators of environmental change or responses to management. Such estimates are also valuable in modelling population growth. We report estimates of nest survival for burrow-nesting Grey-faced Petrels (Pterodroma gouldi) from four islands off the north-eastern coast of New Zealand. We surveyed the contents of breeding burrows for up to four breeding seasons and followed the fates of 1371 eggs. We used a logistic-exposure modelling approach to investigate the effects of island, year, local burrow density and occupancy rate on nest survival. Daily nest survival varied between years and islands but declined with increasing local burrow density across all islands. Local burrow occupancy rate had no detectable effect. We estimated overall rates of breeding success on our island groups of 11% (95% confidence interval 9–14%) to 28% (26–30%). The negative density-dependent relationships between local burrow densities and productivity add to the growing evidence for this effect in burrow-nesting seabirds worldwide, in contrast to trends in surface-breeding species. The variation in productivity between our study colonies may be linked to the restoration histories of the islands and suggests that data from one location should be used cautiously when guiding management of the same species elsewhere.