Urbane en agrarische Scholeksters Haematopus ostralegus in en rond Assen in 2009-2012

In the city of Assen, Drenthe (67.000 inhabitants) in 2009-12 35-51 mainly roof-breeding pairs of Oystercatchers were monitored and the same was carried out in farmland in the vicinity of the city with 9-14 breeding pairs. In 2009 a colour ring scheme was started so birds could be recognised individually (Figure 1, Table 1). The population in built-up areas increased in 2008-12 and decreased in farmland (Table 2). The urban Oystercatchers performed better in hatching eggs (Table 3, Figure 2) and produced approximately four times more fledglings than their neighbours in farmland. The colour rings revealed a strong site fidelity in adult breeders, especially in the urban birds, which moved on average 131 m (n=8) from one year to the next. Farmland birds moved on average 1298 m (n=8) between years and one farmland bird moved 3700 m to an urban site. Outside the breeding season four adults were sighted along the Dutch Waddensea coast and three in the Delta area in the SW of the Netherlands. Two juveniles were observed at the same locations (Fig. 3) and two others were sighted along the French coast at 960 respectively 420 km from their place of birth.