Reproducción del Gavilán Ceniciento Circus cinereus en la Patagonia Argentina

Abstract

Data on the breeding biology of the Cinereous Harrier (Circus cinereus) in Santa Cruz province, Argentina, are given. The study was conducted from 20 Sep 1987 to 5 Jan 1988. Hamers nested colonially in a marsh dominated by Juncus sp. Ten nests were placed in 3,5 has. Mean distance to the nearest conspecific nest was 46,4 m. Nesting density was l nest per 0,35 ha. Mean clutch size was 3,5 ± 0,91 eggs. Incubation period in one nest with 5 eggs was 28- 32 days. 54 % of the eggs hatched. Breeding period extended from later Sep to later Feb or early Mar. Hamers defended collectively the nests from humans or raptors. One case of polygyny was recorded. Vocalizations, aerial displays and nestling development are described. The breeding biology of the Cinereous Hamer appears to be similar to that of other Circus species except for its colonial nesting habits, collective defenses of nests and absence of intraspecific attacks between nesting birds.