Body weights and dimensions were recorded for 70 fledglings at Heron Island, on the southern
Great Barrier Reef. Results show that the length of the longest primary feather and tarsus were
·significantly different between habitats, with the Fringe showing highest and Buildings area showing
lowest means. This outcome probably resulted from most nestlings measured in the Buildings area
being the progeny of early breeders. Variability in the breeding cycle may have confounded the
analyses of body weight and of dimensions. When data were grouped according to the timing of laying,
early breeders showed significantly lower hatching and breeding success. Both these results are useful
for detecting inter-annual differences at this locality or for comparisons with colonies located elsewhere.

The population size of the Black Noddy Anous minutus was monitored over five years at Heron
Island, a 13.5 ha coral cay located on the southern Great Barrier Reef. The population which reached
around 67 000 breeding pairs in 1989 appears to be increasing, although the rate of expansion is
difficult to determine. Highest nesting densities are found in large Pisonia grandis, probably due to
higher nesting site availability. Nesting densities appear to be independent of the degree of habitat
modification; differences in breeding success with disturbance remain to be investigated.