First records on incubation period and development of chicks of the vari- able hawk (Geranoaetus polyosoma) Quoy & Gaimard in captivity

Abstract

Two captive-bred pairs of Geranoaetus polyosoma were monitored between 2010 and 2012 at a private raptor bree- ding-centre in south-west Spain. The variable hawks, originally from the coast of Peru, mated during the northern spring, as do other species of raptors in the wild at these latitudes. In- cubation lasted 35–36 days, similar to other taxonomically related species. The male provided the nesting material but the female arranged and built the actual nest structure. The female carried out most of the incubation duties. Here we report when and how they mate, each episode averaging 9.75 seconds. The average clutch size was 1.82 eggs. The shape, size (56.8 x 42.6 mm) and color (dirty white with gray stains and irregular reddish spots at the base) of the eggs are described. The hatching of the eggs from the initial perforation of the shell to the moment of birth took between 12 and 60 hours. An early loss of eggs led to a clutch being replaced. A daily control of the weight of five chicks during their first 40 days of life showed that weight gain was moderate and gradual for the first 10 days; between 10 and 30 days, weight gain was considerable, falling again after 30 days. The breeding period in captivity in relation to different populations of this raptor, as well as the influence that captive conditions may have on birds, are discussed.