The breeding pattern is partly influenced by the annual variation in available habitat; therefore, distribution is overestimated due to the cumulation of three years of fieldwork. Widely distributed species; breeding numbers in the river area and the east of the Delta (often more than 10 bp/square) are clearly higher than elsewhere (in general 1-3 bp/square). Range expansion since the mid-1970s by colonisation of new habitats, especially in the Delta area (reclaimed areas, renaturation projects), but elsewhere as well (construction works, sand and gravel pits). More or less natural habitats are nowadays mainly confined to the River Waal (where 40% breeds on or near riverside). The national population comprised 750-1100 bp in 1998-2000 (800-1300 in 1973-77).
- SOVON Vogelonderzoek Nederland 2002. Atlas van de Nederlandse broedvogels 1998-2000. Nederlandse Fauna 5: 1-584. Nationaal Natuurhistorisch Museum Naturalis, KNNV Uitgeverij & European Invertebrate Survey-Nederland, Leiden.