Buizerds Buteo buteo in Oost-Twente en aangrenzend Duitsland in 1974-83: effecten van verstoring en grondgebruik op de populatiedynamiek

During 1974-83, the impact of human disturbance and land use on distribution, density and breeding biology of Buzzards was studied in the eastern part of The Netherlands 1974-75,40 km² since then). Both areas consist mainly of farmland with a scattering of woods (up to 300 ha), woodlots and marshland (300 ha in Germany). Meadows – and to a lesser extent cereals – predominated in the 1970s, but were gradually replaced by green maize. The higher human density in the Dutch part of the study area (and denser infrastructure, including paths), as compared to Germany, enabled a comparison of the impact of human disturbance (mainly recreation, as day trips) on the breeding performance of Buzzards. Human disturbance was found to profoundly impact Buzzards during the preincubation stage, especially with regards to nest site choice. Edges and sites at >75 m distance from the nearest path were preferred. Human disturbance was also found to impact breeding success (excluding nests disturbed by forestry activities and those deliberately destroyed): 22% of 64 nests within 75 of the nearest path/road failed, compared to 7% of 129 nests at >75 m of paths. Overall breeding success (% nests successful) was higher in Germany (75% of 256 pairs) than in The Netherlands (65% of 155 pairs), but the average number of chicks per successful nest did not differ (respectively 2.2 and 2.1). Mean breeding density declined synchronously in both study areas, irrespective of annual fluctuations, from 6 pairs/10 km2 of landscape in the early 1970s to 4 pairs/10 km2 in the early 1980s. This decline coincided with the above-mentioned shift in land use, probably via declining food resources (mainly voles Microtus arvalis and Clethrionomys glareolus and Moles Talpa europaea, important prey as recorded during nest visits).