Wintering White-tailed Eagles Haliaeetus albicilla in the Netherlands:Aspects of habitat scale and quality

• Main Authors: van Rijn, Stef, Zijlstra, Menno, Bijlsma, Rob G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2010
• Subjects: wetlands; scale; dynamics; food supply; White-tailed Eagle; future perspectives; RIVER; Haliaeetus albicilla; White-tailed eagle
• Online Access: https://hdl.handle.net/11370/601469b2-2340-45ab-bce8-07e9572c6aef; https://research.rug.nl/en/publications/601469b2-2340-45ab-bce8-07e9572c6aef

The coastal wetlands of The Netherlands have always served as winter haunts for juvenile and immature White-tailed Eagles from breeding populations further north and east. Even as these populations were at their lowest ebb by the 1960s and 1970s, each winter a few individuals showed up, invariably favouring large wetlands with a good supply of wintering, mainly herbivorous, waterfowl. An analysis of the presence of eagles in the wetland Oostvaardersplassen showed that wintering numbers as well as the duration of individual stays increased as a function of the number and biomass of waterbirds present. During the pioneering stage of this newly reclaimed area the dynamic vegetation produced huge seed supplies that attracted vast numbers of herbivorous waterbirds. The increase in eagle numbers in the Oostvaardersplassen reserve preceded the recovery of the northern and eastern breeding populations of White-tailed Eagles, but did not increase any further after reaching a maximum of 3-4 wintering birds, despite the fact that wintering numbers elsewhere in The Netherlands continued to rise in the wake of the increasing breeding population elsewhere in Europe. It is argued that 'core area' Oostvaardersplassen became saturated each winter in the 2000s. Additional eagles reaching The Netherlands spent the winter at alternative sites with smaller food supplies. In 1997-99, new waterbodies were created in the dry border zone of Oostvaardersplassen. The subsequent boost in waterbirds and fish may have triggered- in combination with the presence of undisturbed breeding habitat - the summering, and eventual breeding, of White-tailed Eagles from 2004 onwards. Water management towards improving dynamics in larger wetlands (both estuarine and riverine) may further boost food supplies for waterfowl and, hence, create suitable habitat for White-tailed Eagles elsewhere in The Netherlands.