Physical environmental influences on breeding performance of the fairy prion (Pachyptila turtur)

Abstract

Breeding seabirds are affected by predation, food distribution, competition for food, nest site availability and environmental pressures (Ashmole 1971). Using 11 years of nest monitoring data and eight years of chick measurements of fairy prions (Pachyptila turtur) at a colony near Dunedin, New Zealand, I investigated the link between physical environmental factors, breeding success rates and chick fledging size. Data from the same colony were then used to analyse the relationship between chick fledging size, likelihood of natal-colony recapture and age at first recapture. The colony had remarkably steady breeding success rates and chick fledging mass throughout the study period, perhaps due to a consistent source of local food, the use of behavioural buffering mechanisms by fairy prion parents, or due to an overriding effect of nest-site limitation. Fledgling wing lengths were slightly different between years, and these differences could be predicted by late-winter values of the Southern Oscillation Index (SOI) and summer sea surface temperatures (SST). In years of high SOI and high SST, fairy prions fledged with longer wings. This could be a result of increased availability of Nyctiphanes australis, the main prey of fairy prions, in these conditions. River flows and rainfall were unrelated to any of the chick measurements, probably because the influence of freshwater on the marine system near Dunedin acts at smaller timescales than those studied here. Investigation of fledging measurements, cohort and likelihood of recapture for the 2004 and 2005 fairy prion cohorts showed no evidence of a link between fledging size and likelihood of recapture, but there was a link between cohort and probability of recapture. The 2005 cohort had unusually low six-year recapture rates, and also shorter-than-average wing lengths. These findings suggest that fledging wing lengths are more sensitive to environmental influences than are breeding success or fledging weights; also, the combination of low sea temperatures and an El Niño event in 2005 may have led to a reduction in Nyctiphanes availability, ultimately affecting post-fledging survival of the 2005 cohort.