Blauwe Kiekendieven Circus cyaneus foerageren en slapen in percelen ongedorste gerst in Drenthe

Hen Harriers wintering in Drenthe normally roost on wet heatherland. Due to abundant rainfall, several fields with barley and beets (c. 3 ha in size) could not be harvested in autumn 1998 and laid fallow throughout winter and early spring. Consequently, Field Voles Microtus arvalis and Harvest Mice Micromys minutus were very abundant, as were several seed-eating passerines as Skylarks, Starlings, Fieldfares, Yellowhammers, Reed Buntings and Tree Sparrows. The fields attracted up to five foraging Hen Harriers at a time. Up to 12-13 January 1999, an adult male, three immature males and an immature female were present. This situation changed after 12 and 13 January 1999, apparently caused by snowfall, and smaller numbers of Hen harriers used the site. From 27 January onwards, plot I was increasingly defended by an immature female; she evicted tresspassers during daytime and thereby proved that immature female Hen Harriers can successfully defend feeding sites against adults. Plot II was alternately used by one or two immature birds, at least one of which was an immature female (the other probably an immature male). Other birds apparently hunted elsewhere and used the site only for roosting (Table 1), Throughout winter 1998/99, immature birds were more numerous than adults (the latter mostly males); after 12 February adult males were completely absent. The roost was deserted from 19 March onwards, despite the presence of an immature male and ditto female during daytime. A second-winter male got fatally entangled in barbed wire at the roost (Foto 3). Pellet analyses showed that Field Voles constituted the main prey: 264 Microtus arvalis, 2 M. agrestis, 2 Sorex araneus/coronatus, 1 Micromys minutus and 23 birds. Twelve pluckings added 5 Turdus pilaris, 3 Alauda arvensis, 2 T. merula and 2 Sturnus vulgaris to the list of prey items.