Growth and development of nestling brown Goshawks Accipiter fasciatus with details of breeding biology

Abstract

The nesting chronology of one captive (5 nestings) and two wild pairs of Brown Goshawk Accipiter fasciatus, and the growth and development of twelve captive-bred and five wild-bred nestlings are described. Nest building commenced three to four weeks before egg-laying and involved both partners. Moult in the female started, at the innermost primary, about five days before the first egg was laid. Clutch size was two to four (median 3) and eggs were laid at two to four day intervals (median 2) with incubation usually commencing with the second egg. Incubation, by both sexes, lasted thirty days (range 29-31). amongst the shortest recorded for accipiters. Nestlings hatched in a coat of sparse white down which was gradually replaced by a thicker, browner, down by twelve days of age. At six days wing pins had emerged and at eight days tail pins. Fledging occurred at thirty to thirty-one days (range 28-37). Males usually reached various developmental and plumage stages a day or so before females. Wing length increased linearly between the emergence of the wing pins and thirty-five days of age and gave the best estimate of age. Weight increase was more or less sigmoid; adult weight was reached by fledging in males and slightly after fledging in females. Females were not consistently separable from males by weight until about three weeks of age, and their wing and tail length were similar to those of males until about seven weeks of age. Some methods for the estimation of age and sex are given. Growth rates were rapid in relation to body size.