Breeding Avifauna of the Chesterfield Islands, Coral Sea: Current Population Sizes, Trends, and Threats.

Abstract

This paper reports on post-1991 census data and on the breeding phenology of seabirds of the Chesterfield-Bampton and Bellona groups of coral islets in the Coral Sea. In total, 13 resident bird species were observed [Wedgetailed Shearwater (Puffinus pacificus), Masked Booby (S. dactylatra), Brown Booby (Sula leucogaster), Red-footed Booby (S. sula), Lesser Frigatebird (Fregata ariel ), Great Frigatebird (F. minor), Black Noddy (Anous minutus), Brown Noddy (A. stolidus), Crested Tern (Sterna bergii), Sooty Tern (S. fuscata), Fairy Tern (S. nereis), Black-naped Tern (S. sumatrana), and Buff-banded Rail (Gallirallus philippensis)]. Segregation for nesting habitat was similar to that previously observed on other coral-reef islets of the Coral Sea. Breeding periods were either in the winter (Masked and Red-footed Boobies, Frigatebirds, Fairy Tern) or in the summer (Wedge-tailed Shearwater, Black and Brown Noddies, Crested and Black-naped Terns) or year-round (Brown Booby). Sooty Terns bred twice a year (summer and spring), but this was not consistent across years. Estimates of breeding population sizes for the whole Chesterfield-Bampton and Bellona groups are proposed for Wedge-tailed Shearwater (90,000 to 106,000 breeding pairs), Masked Booby (280–500 pairs), Brown Booby (3,800–5,800 pairs), Redfooted Booby (7,200–7,300 pairs), Lesser Frigatebird (1,600 pairs), Great Frigatebird (350–480 pairs), Black Noddy (29,000–45,000 pairs), Brown Noddy (15,000–23,000 pairs), Crested Tern (80–100 pairs), Sooty Tern (11,000– 46,000 pairs), and Black-naped Tern (70–90 pairs). Interannual fluctuation in breeding population size was apparent in Wedge-tailed Shearwater. Over the last 30 yr, an increase in Brown Booby abundance was noted, whereas declines are suspected for the Fairy Tern and Buff-banded Rail. Among the threats to nesting seabirds are stress and other disturbances caused by human frequentation, including poaching of seabird chicks and introduced mice.