Het voorkomen van de Boomvalk Falco subbuteo rond Nijmegen sinds 1970

Around the city of Nijmegen (eastern Netherlands), 6-12 pairs of Hobbies nested annually in an area of 30.000 ha of wood- and farmland during 1970-2000. The population was more or less stable since 1989, with on average 7.7 pairs/year in 1989-94 and 9 pairs/year in 1995-2000 (coverage better in latter period). These pairs occupied 24 sites, of which only one was used each year (three others possibly also). In 1989-2000, 9 sites were used once, 6 sites twice and 4 sites thrice. However, the distribution within the study area showed a clear temporal change. As compared to the period of 1970-76, Hobbies declined from 9 to 3 pairs in the woodlands on sandy soil south of Nijmegen (c. 3300 ha), whereas the number of occupied sites increased from 1 to 6 in the farmland northeast of Nijmegen (c. 27.000 ha). In the late 1990s, Goshawk Accipiter gentilis density in woodlands near Nijmegen amounted to at least 1 pair/300 ha. In the farmland north of Nijmegen, only 3 pairs of Goshawks nested, i.e. 1 pair/9000 ha. It seems that the disappearance of Hobbies from large woodlands coincided with the increase of Goshawks (to 11 pairs) in the same area. The increase in open farmland with a much lower density of Goshawk suggests a shift in habitat choice by Hobbies, probably instigated by the Goshawk trend in woodland.