Breeding biology of the black-chested eagle Geranoaetus melanoleucus (Aves: Accipitridae) in central Chile

The breeding biology of the black-chested eagle (Geranoactus melanoleucus) was studied during a 2-year period (July 1987-January 1989) in San Carlos d e Apoquindo, central Chile, The beginning of the reproductive period was ev ident by the increased number of couple-flights. Courting behavior included synchronized (lights, cooperative capture of prey and transport of nest ma terial, as well as copulation. Prey exchanges between adults occurred throu ghout the year, although outside the breeding season they were uncommon and forced by the female, There were 4.7 nests/couple, a value that is in the upper limit of what has been reported for large eagles. During the non-bree ding season, nests were only occasionally visited by the eagles. Before lay ing, males visited the nest more frequently than females, but for shorter p eriods of time. Visits to alternative nests carrying prey and nest material were observed in all three couples. The average clutch size was 2.3 eggs ( SD = 0.5, n = 6), with both males and females incubating, and hatching succ ess was 100 %. Twenty five days after hatching, flight feathers started to appear in the wings and tail of chicks; after 35 days, chicks started eatin g by themselves prey items brought to the nest, and after 59 days they left the nest. While tending, females spent more time in the nest than males, a lthough with a tendency of adults to diminish the time spent in the nest ov er time. Seventy nine percent of the chicks survived, which can be consider ed a high reproductive success, explained by the high availability of prey in the study site, mainly European rabbits. The chicks remained in the adul t's territory for 10 months and gradually started to reduce their presence in the area. This was coincident with the occurrence of the next laying per iod and an increased adult intolerance. These data concur with the pattern described in the literature for other eagles.