NDFF Waterbird survey by airplane for the IJsselmeer, Markermeer and IJmeer

Counting birds that fly at an altitude of 500 to 600 feet (ca. 150 to 180 metres), and at an average speed of 70 to 80 knots (130 to 150 km/ph.). Birds are observed by eye or with binoculars (magnification between 7 and 10 times). An observer does the counting and is accompanied by a writer who makes additional observations. Positive observations without zeros. Dataset available via https://www.ndff.nl/english / [e-mail] https://www.ndff.nl/overdendff/validatie/protocollen/14-207-rws-vliegtuigtelling-vogels-ijsselmeer-ea/