Roofvogels op het Fochteloërveen en omgeving in de winter van 1994/95

During September 1994 through March 1995, the heath and farmland of Fochteloërveen and surroundings in the northern Netherlands (3100 ha, Fig. 1) were systematically surveyed to gain insight in habitat use and choice of prey of wintering raptors. Time spent and species investigated are mentioned in Table 1. Raptors were mapped, their behaviour noted down and pluckings and pellets searched for (beneath perches and on roosts). Hen Hamers used the heath as roosting site, of which two were located (Fig. 2). Males predominated at the roosts (93%, Table 2), but only 48% of the Hen Harriers hunting over the heath were male. Most roosting males were adult (80% of those aged and sexed), but 65% of the females were in their first year. Most females foraged over the the heath, rather than in farmland (Table 2). Pellets collected at the roosts contained 71 common voles, 1 harvest mouse and 12 birds (among which a ringed Robin). A depredated first year female Hen Harrier was presumably killed by a Goshawk. Most observations of Common Buzzards related to birds along the margins of heath, farmland and forest (Fig. 3). Of 11 age-identified birds, only one was adult. Foraging took place on foot (8x), from perches (43x) and by hovering over the heath (2x). The following prey items were found in pellets: 2 moles, 6 common voles, 2 field voles, 5 water voles, 1 musk rat, 3 unidentified mice/voles and 3 birds. At least four Rough-legged Buzzards frequented the area, i.e. three adult males and an adult female. One of the males used a nearby stubble field for hunting, the other birds restricted their foraging activities to the central heath (Fig. 4 and 5). Methods of hunting were hovering (58x) and perching on elevated posts (36x) or on the ground (9x). Hovering was mostly restricted to birds hunting on the heath, presumably because of the tall vegetation there. Nine pellets were on average 54.0 mm long (SD=10.7), ranging from 37.4 to 72.0 mm. The average width was 26.6 mm (SD= 3.5), with a range of 18.0 to 28.0 mm. The pellets contained the following prey items: 1 hedgehog, 25 water voles and 1 wood mouse. Only four out of 35 Merlins observed were sexed: 2x adult male and 2x female/first year. Most Merlins were seen in late aftemoon and in the evening, presumably relating to birds visiting their roost (Fig. 7). Four pellets measured 15.0x8.9, 23.4x11.9, 26.2x11.3 and 30.3x12.0 mm and contained remains of three seed-eating and one insectivorous bird(s). Goshawk, Sparrowhawk and Kestrel (Fig. 6) were rarely seen on the open heath, either because they foraged in forest margins or over farmland. Raptors (including owls) at Fochteloërveen showed an almost complete segregation in habitat use and/or prey hunted: Common Buzzards perch-hunting in farmland (mammals), Rough-legged Buzzards hover-hunting on the heath (mammals), Hen Harders fly-hunting mammals and birds on heath and farmland (with indications of a segregation in habitat use between the sexes), and owls mammal-hunting at night (Table 3). The presence of heaths seems to be particularly important for Hen Harders, especially as roosting sites.