REPRODUCTIVE PARAMETERS OF THE GRAY GOSHAWK (ACCIPITER NOVAEHOLLANDIAE) AND BROWN GOSHAWK (ACCIPITER FASCIATUS) AT ABERGOWRIE, NORTHERN QUEENSLAND, AUSTRALIA

Thirty-one A. novaehollandiae breeding attempts on 14 territories were located near Abergowrie, Queensland (18 degrees 27' S, 146 degrees 0' E) between 1986 and 1989. Twenty-nine breeding attempts by A.fasciatus were located on 14 territories in the same study area. Both species began nest construction around the first week of September. Egg-laying was complete by mid-October. Mean clutch size of A. novaehollandiae was 2.0 and of A.fasciatus was 3.0. Both species incubated for about 30 days. The nestling period of A. novaehollandiae was 30-38 days; that of A.fasciatus was 32-37 days. Post-fledging period for both species was 38-43 days. Neither species bred outside the 'spring' (August-December) period. Both species tended to nest near the edge of large (>50 ha) forest or woodland tracts bordering young pine P. caribaea plantations. They did not nest near sugar cane. Accipiter novaehollandiae tended to nest in larger trees, which occurred in denser habitats: closed forest and tall open woodland. Nests were placed on forks at the end of major horizontal or slightly oblique branches. Accipiter fasciatus tended to construct nests in smaller trees; nests were correspondingly closer to the trunk. Differences in the overall size of nest trees were attributed to habitat differences. Interspecific distances to nearest-neighbour were less than intraspecific distances. Close interspecific nesting was related to habitat heterogeneity and prey availability within the study area. Ninety-four percent of A. novaehollandiae nests of known outcome were successful, while the success rate of A.fasciatus was 62%. The total offspring production per pair of the species was similar, but the greater rate of nest failure for A.fasciatus meant that this species fledged fewer young per initial nest than A. novaehollandiae. Tropical thunderstorms were responsible for most nest failure and nestling deaths. Both species used nests repeatedly only after successful nesting.