Overzicht van het lopende roofvogelonderzoek in Nederland in 1995

During 1995, large parts of The Netherlands were again surveyed for raptors, with the emphasis on monitoring breeding birds in fixed plots of varying sizes and collection of basic data on breeding biology (onset of laying, clutch size, number of fledglings, breeding success, causes of failure), population dynamics (age composition among territory-holders, turnover, secondary sexratio) and persecution. All together, information on raptors was gathered in 570 5x5 km-squares, mostly in the northern and southwestern Netherlands and biased towards raptors breeding in forests on sandy soil (Figure 1). Basic data on 11 raptor species were collected, in some species covering almost the entire Dutch population (Montagu’s Harrier, Peregrine), in others 7-28% of the Dutch population. More than 100 nest cards were received for Marsh Harrier, Gosghawk, Sparrowhawk, Common Buzzard, Hobby and Kestrel each (Table 1). Moreover, several long-running schemes on Marsh Harrier, Hen Harrier, Goshawk, Sparrowhawk and Kestrel are not included in these totals. Elsewhere in this issue, much of this information is quantified and further elaborated by region. Human persecution persisted unabated throughout 1995, with at least five mass-poisonings (mainly of Common Buzzards). Of 138 dead raptors collected for an aulhopsy, 61 appeared to have been poisoned and 4 shot (Table 2). Several raptors were not suitable for an authopsy (classified under “negative”), indicating a still higher incidence of poisoning. Common Buzzards were most often victimised by poisoning, probably resulting from their habit of taking carrion and their abundance as a breeding bird and winter visitor. Commonly abused poisons were aldicarb, carbofuran and parathion (Table 3). Poisoning incidents occurred especially in the northern and southeastern Netherlands, i.e. in regions with large raptor populations in combination with very active raptorphiles (Figure 2). Persecution seemed to focus on raptors in late winter and early spring (January through April), probably because an increase in display activities boosts the profile of breeding birds and high numbers of winter visitors from E- and N-Europe are still present (Table 4).