Grauwe Kiekendieven Circus pygargus in Nederland in 2001

In 2001, 35 pairs of Montagu’s Harrier were located in The Netherlands (Fig. 1), ten pairs less than in 2000 but not much different from data in the 1990s (Fig. 2). Breeding is mostly restricted to Lauwersmeer (4 pairs in a wetland, in sympatry with 2 pairs of Hen Harrier Circus cyaneus and 22 pairs of Marsh Harrier C. aeruginosus; cf. Fig. 3), the province of Groningen (27 pairs, with 21 nests in winter wheat, 2 in alfalfa, 2 in natural vegetations en 2 nests at unspecified sites), in Flevoland (3 pairs, farmland) and probably in the province of Drenthe (several observations indicating a breeding pair near Hijkersmilde; Fig. 4). Vole numbers were poor, as indicated by vole trapping lines in Groningen (1.38 voles/100 trapping days, as compared to an average of 6.32 voles/100 trapping days in 1992-2000) and in Flevoland (mean 1.61 voles/100 trapping days). This was reflected in the high diversity of prey items collected in and near nests and in pellets (Appendix 1, Table 1). Hares, passerines typical of arable land (skylark Alauda arvensis, yellow wagtail Motacilla flava and meadow pipit Anthus pratensis) and starlings Sturnus vulgaris were important substitutes for voles. Montagu’s Harriers seemed to prefer recently fledged passerines (60% of 535 passerines in 1992-2001); an even higher proportion of newly born hares/rabbits was recorded, i.e. 97% (n=68 in 1992-2001). Annual and regional differences in the proportion of prey groups are clearly demonstrated in resp. Tables 1 and 2, most likely correlated with annual fluctuations in prey availability and regional differences in habitat, prey numbers and prey diversity. Recovery data from birds ringed as nestlings show both natal philopatry in Dutch Montagu’s Harriers and exchange with breeding areas further away in Germany (Table 3 and other data). In the next few years, efforts to recapture ringed birds will be stepped up, whereas wing tags will be used to identify birds individually. International cooperation is urgently needed, and a network of Monty enthusiasts is presently involved in fine-tuning research on this threatened raptor in Europe.