Derde broedgeval van de Zeearend Haliaeetus albicilla in Nederland

In 2008, the only pair of White-tailed eagles in The Netherlands bred again in the Oostvaardersplassen, albeit using a newly built nest some 350 m apart from the previous one. The new nest was more difficult to observe. Hence, the collected data are rather meagre compared to the previous two nestings. The new nest was detected in March 2008, when the birds were already incubating. Nest building at the old nest was observed up to and including February, when both pair members frequently deposited branches on the rim of the nest. Despite the building of a new nest, we believe that the pair composition remained the same. During the preceding winter, never more than two adults were recorded at any one time (and this area is intensively watched by birders, with data submitted to www.waameming.nl). Moreover, the reproductive performance in 2008, as compared to 2007 and 2006, fits the pattern of improvement with increasing age and parental fine-tuning (the female was bom in 2003 in northern Germany). The new nest was built in the cross-section of two willows Salix sp. leaning against each other. This provided a sturdy basis for the 1.6 metre of nesting material. Nest height was 8.7 m (measured from the top), i.e. slightly lower than the previous nest. The diameter was 1.75 x 1.78 m (top). The nest consisted entirely of dead branches of willows, including some taken from a beaver’s Castor fiber lodge. The pair raised two chicks (compared to one chick each in 2006 and 2007), a male and a female (according to morphometries, and validated by a DNA-analysis), which fledged late June (start of egg laying estimated at I March). Prey remains collected on the nest on 15 May (during ringing) included 2 Greylag Geese Anser anser, 5 Coots Fulica atra, 2 Musk Rats Ondatra zibethicus and 5 Carps Cyprinus carpio. This list closely resembles the availability of abundant prey species in the Oostvaardersplassen in summer, among which some 500 pairs of Greylag Geese (with on average 5-6 goslings each), some 20.000 moulting Greylag Geese, about 1200 Musk Rat lodges, large numbers of ducks and Coots Fulica atra, and high densities of Carp and Bream Brama abramis. Despite the small number of prey items, and the inevitable bias in a diet description associated with prey remains collected on nests, the predominance of geese, ducks. Coots, Musk Rats and fish seems realistic (also given the data collected in 2006 and 2007). Next to nothing is known about food choice in winter.