Een nieuwe methode om de Sperwer Accipiter nisus beter in beeld te krijgen

Studying Sparrowhawks in their breeding haunts, especially when individual recognition is a prerequisite for understanding their ecology, is not easy. In the past, comparison of moulted feathers was used to identify individual birds from one year to the next, but this requires the collection of the same primaries across years. Moreover, very few if any moulted feathers of males were found on the breeding site (males spend most of their time hunting, away from the nest). In the province of Groningen, therefore, colour-ringing was initiated in 2020. However, apart from the occasional female it turned out that reading colour-rings on Sparrowhawks in the field was easier said than done. The solution was brilliant in its simplicity: supply the nesting habitat with artificial sitting posts that are irresistible for Sparrowhawks to use, i.e. horizontal branches wedged between neighbouring trees at a height of several meters, between 10 and 30 m away from the nest. This trick is particularly effective in tree stands with few opportunities for plucking prey. The artificial sitting post (or a tree close by) is equipped with a trap camera with conversion lens (for photos of objects some 50-150 cm away), which is motion-triggered. This novel method of individualizing Sparrowhawks was first attempted in 2021. Already on 31 January, a male was digitally captured. In ten territories, only the male was photographed in two, male ánd female in another six. One male was photographed in two different territories.All photographed birds could be aged (1x 2nd calender-year, 19x older), and all birds were photographed sufficiently well to record absence/presence of a ring. In several territories it was possible to prove that three different birds were present. Copulations were recorded 12 times between 28 March and 30 April. A variety of other wildlife was photographically captured as well, including Buzzard, Goshawk, Tawny Owl, Long-eared Owl and several mammalian species. A number of different cameras was tested, i.e. Wildgame Innovations (SC20B20-7 and L20B20F2), Browning (2020 Recon Force Edge), and Bushnell (Trophy Cam and Natureview with standard conversion lens). The latter turned out to be the most profitable in terms of providing useful photographs.