Reproductive success and chick growth of Pacific Gulls Larus pacificus in the Furneaux Group, Australia

Abstract

The Pacific Gull Larus pacificus is a large larid endemic to Australia, widespread in the southern half of the continent. Little is known about its breeding biology. I present data from 131 nests across nine islands in the Furneaux Group, Tasmania. Pacific Gulls demonstrated a protracted laying period between 16 October 2003 and 2 January 2004, producing on average 2.11 ± 0.64 eggs per clutch. Egg size and mass decreased through the laying sequence. Eggs from three-egg clutches were larger and had greater mass than eggs from smaller clutches. Overall, 45% of eggs hatched, with wide disparities in hatching rates among islands. Solitary pairs were most successful, hatching 100% of their eggs. Estimation of growth over the first 60 days of chicks' life displayed an S-shaped curve, typical of logistic growth, but none reached the parental asymptotes for any of the body measurements. Overall reproductive success was 26%. As with hatching, pairs nesting solitarily on islets had the highest fledgling success. Amongst islands with more than one nest, Mid Woody Island had the highest fledgling success, with 52% of all nests initiated having a chick survive. Pacific Gulls are threatened by increased urbanisation, anthropogenic disturbance and possibly intra-specific competition from Kelp Gulls L. dominicanus. These data are the first to be published from the Furneaux Group and will assist in the future management of the species.