The Wadden Sea and Delta areas (max. 34,500 and 31,600 bp, respectively, in 1998-2000) hold by far the highest numbers and largest colony (10,500 bp at Saeftinge, Delta). Since the 1980s, breeding numbers in the two areas developed differently (decrease in Wadden Sea caused by food shortage, increase in Delta, although numbers have stabilised by now). On the mainland, colonies in the coastal dunes became almost deserted as a result of intense predation by red foxes. In response to this, the species started to breed on buildings here (at least 20 towns, 1600 bp or more). The national population in 1998-2000 consisted of 62,000-67,000 bp, more than in 1973-77 (max. 53,000) but less than in the mid-1980s (90,000).
- 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.