De Havik Accipiter gentilis in en rond Amsterdam: opkomst, verspreiding, voedsel en gebruik van het landschap

In The Netherlands Goshawks have been expanding their breeding range westwards since the late 1970s. Based on a variety of sources, settlement and subsequent colonization of Amsterdam (including wide surroundings with towns and villages like Zaandam, Hoofddorp, Amstelveen, Aalsmeer, Abcoude, Ouderkerk a/d Amstel, i.e. 450 km2 of which some 60% built-up including industrial areas and airport Schiphol) by Goshawks is reconstructed and described. After initial settlement in 1986 numbers remained low till the mid-1990s (0-7 pairs), followed by a steady increase to more or less stable numbers in the mid-2010s (peak of 36-40 territories in 2015-16). Strictly urban areas were avoided for breeding. Most pairs occupied territories in suburban areas with recreational grounds, parks, forest plantations, wooded strips, and – farther away – overgrown wetlands. This is reflected in the choice of nesting trees, i.e. mostly Populus sp. (21 out of 55), Salix alba (9x), Betula sp. (8x) and Alnus glutinosa (6x), with a scattering of other tree species (only one nest in a coniferous tree, i.e. Picea abies). Over 1986-2018 a total of 63 territories were identified as being occupied at least once. Of 28 territories occupied in 2018, 14 held a single nest, the remaining 14 had between 2 and 5 nests. Longer occupied territories in the 33-year period had more nests. Nests were on average 48 m from the nearest woodland edge, and on average 66 m from the nearest human activities (some nests even next to footpaths). Overall productivity in 1999-2018 was at least 2.54 fledglings per successful nest (n=91 nests, with 231 chicks present during ringing or nest visit). Between early 2015 and 24 August 2018, a total of 944 prey remains were collected and identified, i.e. 927 birds in 42 species and 16 mammals in 3 species. Birds accounted for 97% in numbers and biomass. Almost one quarter of all prey consisted of feral pigeons Columba livia, Woodpigeon Columba palumbus, Mallard Anas platyrhynchos and corvids. The prey list reflects hunting habitats, ranging from inner cities (feral pigeon, Ring-necked Parakeets Psittacula krameri) to suburbania (songbirds), wetlands (ducks, rails, waders), farmland and woods. Apparently, Goshawks have been able to adept to the dynamic city life. However, fast changes in (sub)urban habitats are rarely conducive to maintain the basic habitat requirements for Goshawks. Several breeding sites have been, or will be in the near future, destroyed following building, reconstruction, road extension and other developments allied with human claims on the environment.