CASTELIJNS H & W CASTELIJNS (2008) Wintering of Marsh Harriers Circus aeruginosus in the provence of Zeeland, The Netherlands. LIMOSA 81 (2): 41-49.

The Marsh Harriers that breed in Europe normally winter in tropical West Africa. However, in the last decades the number of individuals that remains at northern latitudes during the winter has increased. Here, we study the population that winters in the province of Zeeland in The Netherlands, from 1986-2007. The number of wintering Marsh Harriers was surveyed by counts at winter night roosts, complementedwith observations during the day.
      The number of Marsh Harriers wintering in Zeeland has increased from less than 20 individuals in 1986-1990 to 70-180 individuals in 2006 and 2007 (Tab. 1, Fig. 3). One site, the Verdronken Land van Saeftinghe, hosted about 80% of all harriers (Fig. 2). The great majority of birds were in first-winter plumage (90.8%), whereas only 2.9%and 6.3%were adult females andmales, respectively. Winter roostswere found in dense vegetations such as Reed and Scirpus beds. Most foraging birds were seen in saltmarshes and other (semi)natural vegetation along both saline and fresh waterbodies. Harriers were rarely seen hunting in the agricultural areas. Waterfowl (geese and duck) carcasses seem to be the most common food in the winter. Several times it was observed that the harriers took preys that were caught by other raptors.
      The increase in the number of wintering Marsh Harriers coincides with an increase in the local breeding population. Furthermore, the number of wintering birds seems to be higher after a good breeding season. This suggests that the wintering population mainly consists of local young.

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