Predatie van roofvogels en uilen door Nederlandse en enkele Noordrijn-Westfaalse Oehoes Bubo bubo in 2002-06

In the wake of reintroduction programmes in Germany, and a gradual range expansion and increase in numbers in Nordrhein-Westfalen (Germany), Eagle Owls colonised The Netherlands in 1997. Breeding has been uninterrupted since then, although so far only two sites are occupied (southern Limburg, Achterhoek) and the number of pairs is still less than ten. Pluckings (discarded prey remains) and pellets were collected at both sites; smaller prey collections (pluckings and pellets) came from three sites in nearby Germany (i.e, near Wesel, Haltem, Munster), The prey ratio obtained from pluckings and pellets respectively was 5.2:1 (indicating that small mammal prey will likely be underrepresented). All together, 2095 prey items were identified, 1640 from The Netherlands and 455 from adjacent parts in Nordrhein-Westfalen (Germany). The diet consisted of mammals (19.2% in numbers, 22.3% in biomass) and birds (resp. 80.8% and 77.7%), with only 2 dung beetles as an addition (Table 1). Eagle Owls preyed extensively on only a few prey species, as discemable from the Top-3 in local diets: Columba livia, Corvus corone and Oryctolagus cuniculus in Achterhoek, The Netherlands (55% in biomass), Columba livia, Corvus corone and Erinaceus europaeus in Limburg, The Netherlands (51 %), and Columba palumbus, Columba livia and Corvus corone in Wesel, Germany (57%). This indicates a close association with human activities (suburban and agricultural). Eagle Owls took a wide array of raptors and owls as prey (Table 1), mostly Falco tinnunculus, Tyto alba and Asio otus. Compared with the proportion of raptors and owls in other European prey lists. Eagle Owls in The Netherlands and Germany predated equally few raptors and owls, i.e. respectively 3.7% and 2.6% in numbers (in biomass 1.1-6.7%). At present, we have no indications that the predatory behaviour of Eagle Owls endangers distribution and abundance of other owls and raptors. This contrasts with Northern Goshawks, another generalist top predator, that face serious declines in main prey species and consequently diversified their diet (including a steep increase in predation of raptors and owls).