In the 1970s and 1980s several core areas were established by escapes. Breeding was partly stimulated by providing suitable nestboxes. In 1998-2000, these areas are still recognisable, most noticeable in the northeast and south of the Veluwe, a large wooded area in the centre of the country. The national population increased from 3-8 bp in 1973-77 to 200-260 in 1998-2000.
- 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.