The distribution shows strongholds in the east and south of the country, in particular in areas with small, slow-moving streams and vertical banks. Many of the numerous possible breeding records refer to breeding birds from nearby areas. The population is strongly influenced by cold winters, accounting for part of the differences between the 1973-77 and 1998-2000 data. The first were collected in a run of rather mild winters, whilst population levels in 1998-2000 had still not fully recovered from the cold 1995/96 and 1996/97 winters (increasing from less than 90 to over 250 bp in 1998-2000). Population in The Netherlands may vary between less than 50 bp (after cold winters) to 300-400 bp (after a run of mild winters).
- 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.