Variations in the Breeding Biology of the Grey-Faced Petrel Pterodroma macroptera gouldi

Abstract

The Procellariiformes are a diverse seabird order that is well represented in New Zealand. Their conservation maintains both their intrinsic value and ecological function within island ecosystems. The grey-faced petrel is a New Zealand endemic sub-species; one of few Procellariiformes persisting as a large meta-population. However, colonies are variable in size with the majority small and prone to local extinction. The aims of this study were to: (1) compare geographical and annual variations in grey-faced petrel chick growth; (2) investigate parental provisioning behaviours and; (3) investigate the effects of annual variations in breeding success on population dynamics. The breeding attempts of grey-faced petrels from two islands were monitored weekly during the 2013 breeding season: Ihumoana (west coast of New Zealand) and Te Hāwere-a-maki (east coast of New Zealand). Chicks raised on Ihumoana grew significantly faster, fledged earlier and in better condition than Te Hāwere-a-maki chicks. Consequently, the chick rearing period on Te Hāwere-a-maki was significantly longer than on Ihumoana; 139 and 116 days, respectively. Chicks raised on Te Hāwere-a-maki in the 2011, 2012 and 2013 seasons had indistinguishable growth rates and similar chick rearing durations. Hourly weight loss for chicks from Te Hāwere-a-maki in the 2013 season declined asymptotically following a meal. Parents alternated between short and long foraging trips (2-5 days and >8 days, respectively) and appeared to take their chick into account when making decisions as to trip length. Chicks received a meal every 7.7 days, on average. Breeding success on Te Hāwere-a-maki has been similar among the 2011, 2012 and 2013 seasons (36.4%, 40.9% and 45.5%, respectively) despite causes of failure varying between abandonment coupled with starvation (2011, 2013) and predation (2012). Populations experienced growth, within the range of 1.4-9.8% per annum, in simulations with breeding success varied among values calculated for the 2011, 2012, 2013, hypothetical good and bad seasons. Differences in chick growth between Ihumoana and Te Hāwere-a-maki are suggested to reflect differences in the foraging conditions experienced by parents. Results suggest that conditions experienced by chicks raised on Te Hāwere-a-maki in 2013 are relatively typical for this island based on data collected in the 2011 and 2012 seasons. However, it is encouraging that the small Te Hāwere-a-maki population appears to be increasing. These results will inform future conservation strategies for the grey-faced petrel and other closely related Pterodroma species.