Vogels als prooi van roofvogels in een veenweidegebied

In northern Drenthe, and adjacent parts of the province of Groningen, prey remains of raptors were systematically collected throughout the year between late 2001 and 31 December 2006. Formerly grassland on peat soils, much of the 1500 ha of this area has recently been converted into a nature reserve, where some 15 woodlots of 0.1-2 ha provide breeding sites for Buzzard Buteo buteo and Goshawk Accipiter gentilis (4 territories). Reed-covered lake sides are used by up to 3-4 pairs of Marsh Harriers Circus aeruginosus. During the migration periods, and in winter, the study area is visited by Peregrine Falco peregrinus, Hobby F. subbuteo, Merlin F. columbarius, Sparrowhawk Accipiter nisus, Montagu’s Harrier Circus pygargus and Hen Harrier C. cyaneus. Prey remains were collected in woodlots, along fixed transects and beneath much-used sitting posts (fence posts, electricity pylons). Most prey remains were found in woodlots and in hedgerows (63%), the rest in grassland. Of prey species typically associated with grassland, 56% had been plucked in that same habitat (the rest in woodlots and hedgerows). Highest numbers of prey remains were found in winter (October through March), smallest numbers in summer. The latter is suggestive of smaller number of avian predators during summer time, seasonal changes in the composition of the raptor guild (Sparrowhawks and Peregrines almost exclusively in winter), scarcity of mid-sized prey species during summer following environmental changes (conversion of farmland into semi-natural rough grassland), and/or smaller chances of finding prey remains when the vegetation is at its most luxurious. This finding contrasts with the Dutch literature, which shows that most prey remains are collected in summer. It is likely that this is a habitatrelated bias, because most raptor research occurs in woodlands where raptor nests and plucking posts are systematically searched and checked during the breeding season, but where food studies in winter are less popular among raptorphiles.