On the same Goshawk nest where in 1994 a female nestling was detected with aberrant feather development (Bijlsma et al. 1994), a similarly affected nestling male was found in 1996. Rectrices were completely missing, and primaries were either missing or malformed. Body feathers and coverts were full of faultbars (see Photos 2-4). This feather defect was only detected after fledging of three unaffected nestlings; during ringing, at the age of 23-24 days old, as well as during a control a fortnight later, this defect remained unnoticed (Photo 1). Unfortunately, the identity of the breeding female could not be established in 1996 because moulted feathers were not found. However, the breeding female in 1995 was different from the one in 1994 (identity based on moulted feathers), and the 1995-female was again in attendance in 1997. It is therefore highly likely that the 1996-female was the same as in 1995 and 1997, and thus different from the one in 1994, the year in which also feather defects among a single nestling were noticed. The identity of the male could not be established because his moulted feathers were not found. It is speculated that the feather anomalies must have been caused by a genetic defect.

De Takkeling

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Werkgroep Roofvogels Nederland

Henk Jan Ottens, Hugh Jansman, & Roelof Speelman. (1997). Genetische afwijking hoogstwaarschijnlijk andermaal oorzaak van veerafwijking bij nestjonge Havik Accipiter gentilis. De Takkeling, 5(2), 12–16.