Waarschijnlijk geval van bigamie bij Sperwer Accipiter nisus in de Zuidoost-Achterhoek

The start of laying in 13 Sparrowhawk broods in the southeastern Achterhoek in 2002 was on average 2 May, with a range of 19 April through 27 May. One of the broods, visited on 13 July to ring the nestlings, held 6 eggs and a single nestling male (maximum wing chord 78 mm, body mass 125 g); the remains of a seventh egg were detected on the branches underneath the nest. A closer examination of egg sizes and egg markings (Table 1) showed that this apparent clutch of 8 eggs probably consisted of two separate clutches. It remains a mystery whether two females were involved simultaneously, or whether a female took over nest and clutch of another female and added her own clutch. The latter situation might have explained the late onset of laying as calculated from the age of the nestling, i.e. 22 May.