De Sperwer Accipiter nisus als broedvogel in de provincie Groningen en in Noord-Drenthe in 2021

A survey of the province of Groningen and the northern part of the province of Drenthe in 2021 revealed 100 occupied nest sites of Sparrowhawk. Compared to 76 occupied nest sites in 2020, 16 had been deserted, but 14 new sites had been occupied, showing a rather high degree of flux within this population. In the former municipality of Haren (Groningen, 4558 ha), the population was stable at 6-9 pairs in 2012-21. Mean onset of laying in 2021 was 1 May (n=45), close to mean onset of laying of 30 April in 2014-2021 (N=192). Mean clutch size in 2021 was 4.5 eggs (range 2-6, N=18), mean brood size 3.8 (N=45). Nest success in 2021 was 57% (N=100). Failures were recorded during nest-building and early nesting cycle (9%), during incubation (51%) and during the nestling stage (40%, mostly by predation). Sex ratio of nestlings was male-biased: 92 males and 75 females. In 30% out of 44 nests one or more nestlings were parasitized by louse flies. Use of trap cameras, colour-rings and moulted primaries revealed that 2 out of 30 breeding males were 2nd-calender-year (7%), compared 8 out of 42 females (19%). Trap cameras trained on artificial sitting posts were highly successful in elucidating ages of breeding birds and presence of rings (metal and colour), sometimes unequivocally leading to the identification of an individual.