Distribution and population may have been slightly underestimated, as necessary nocturnal census work was not carried out in all areas. At most sites, the species is rare (1-3 bp/square), with some notable exceptions of up to some tens of bp/square. Strong annual population changes, related to fluctuating water tables, frustrate comparison with earlier data. Some local increases can be attributed to renaturation projects or restoration of water levels in nature reserves. Marked influxes (as recorded after late inundations along the rivers) were not observed in 1998-2000 (150-300 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.