Confirmed breeding was recorded in three atlas squares, but two of these (cities of Amsterdam and Rotterdam) were clearly linked to release of birds from local zoos. Possible and probable breeding records (esp. in the river area) are difficult to interpret, as adult and juvenile birds from France and elsewhere may migrate northward during, and soon after breeding season. The species occupied a small colony in the Biesbosch area for decades (up to 10 bp in 1973-77) and incidentally elsewhere, but at present seems to breed only solitarily, apart from zoo releases and their offspring. In 2000 at least 1-6 ‘wild’ pairs and 14 released pairs.
- 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.