Largest numbers (max. 35,000 bp each in 1998-2000) bred in the Wadden Sea and Delta areas. The largest colony, at Europoort-Maasvlakte, held 23,900 bp. In both Wadden Sea and Delta, numbers and distribution have strongly expanded since the 1970s, although numbers in the Wadden Sea tended to flatten in the 1990s. Colonies in the coastal dunes of the mainland were raided in the 1980s by red foxes and disappeared almost completely; part of these birds started breeding in nearby towns and villages, but others left for the Wadden Sea and Delta areas. In 1998-2000, 58,500-72,000 bp were recorded (maximum in 1973-77 was 9700 bp).
- 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.