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.fasciatu s 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 w as 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 w as 38-43 days. Neither species bred outside the 'spring' (August-Decem ber) period. Both species tended to nest near the edge of large (>50 h a) forest or woodland tracts bordering young pine P. caribaea plantati ons. They did not nest near sugar cane. Accipiter novaehollandiae tend ed to nest in larger trees, which occurred in denser habitats: closed forest and tall open woodland. Nests were placed on forks at the end o f major horizontal or slightly oblique branches. Accipiter fasciatus t ended to construct nests in smaller trees; nests were correspondingly closer to the trunk. Differences in the overall size of nest trees wer e attributed to habitat differences. Interspecific distances to neares t-neighbour were less than intraspecific distances. Close interspecifi c nesting was related to habitat heterogeneity and prey availability w ithin the study area. Ninety-four percent of A. novaehollandiae nests of known outcome were successful, while the success rate of A.fasciatu s was 62%. The total offspring production per pair of the species was similar, but the greater rate of nest failure for A.fasciatus meant th at this species fledged fewer young per initial nest than A. novaeholl andiae. Tropical thunderstorms were responsible for most nest failure and nestling deaths. Both species used nests repeatedly only after suc cessful nesting.