Breeding success and nest-site selection of Wedge-tailed Shearwaters (Puffinus pacificus) at Heron Island, Great Barrier Reef

Breeding success of the Wedge-tailed Shearwater (Puffinus pacificus) is examined at Heron Island, a small coral cay of the Great Barrier Reef. The species excavates burrows for breeding in habitat types described as Pisonia forest, Fringe habitat, Southern Fringe and the Buildings habitat in the developed western sector. Breeding success is divided into two stages: hatching success and fledglings produced per chick. Incubation rates (proportion of burrows with eggs) are included in the analysis. Habitat variables likely to influence breeding success and nest-site selection are grouped into correlated sets of composite variables, using principal components analysis. Two models are used to relate the composite variables with nest-site selection and reproductive success. Either burrow occupancy rate or egg density were used in the models to index nest-site selection. The Buildings habitat showed a significantly lower hatching success than other habitats. Moisture in the island substrate had the most significant effect on nest-site selection so that birds occupied burrows in areas of low moisture. Soil strength also had a significant effect on the nest-site selection when the egg density model was used so that eggs were laid in areas of low moisture and high soil strength. High hatching success was associated with high moisture in the substrate, and with a lower density of nesting birds. Early breeders in the Fringe habitat had significantly high mortality of fledglings in comparison with the Pisonia habitat. The primary feather and tarsus length of fledlings were significantly different between habitats. It appears that the shearwaters may have a flexible nest-site seleciton strategy, influenced by the amount of moisture in the substrate and the soil strength. The outcome of differential rainfall intensities probably influences both nest-site selection and hatching success.Submitted in fulfillment of the requirements of the degree of Bachelor of Science (Honours), University of Queensland, 1994