Vogels monitoren per vliegtuig

A description is given of a seabird monitoring programme which commenced in 1990, being the successor of a similar programme which started in December 1984: the aerial surveillance of seabirds and marine mammals on the Dutch sector of the Continental Shelf by the Tidal Waters Division of the Ministry of Transport and Public Works. Methods and (in-)accuracies are explained (cf figures 1-3) while distribution maps of Sandwich Tem in June 1985 and Herring Gull in December 1984 are meant to give examples of some results which will become available in an atlas, due 1991 (figures 4-5). Flying height is ca. 150m at 200 km/h, with transects of I40-170m width, if possible on two sides of the airplane. Each survey takes 3 days of flying covering on average 650 km². It is found difficult to count and identify ’difficult’, or rather ’inconspicuous’, seabirds such as divers, grebes, auks or swimming gulls, but results are considered very good for birds in flight: Fulmar, Gannet, gulls and terns. A maximum of 6 seconds is available for detection, identification and count of each sighting. It is argued that both, aerial and ship-based surveys have their own advantages and disadvantages. Aerial surveys are relatively cheap: a large area can be covered in a small amount of time, while it is easier to plan counts in response to weather conditions. A combination of methods, aerial and ship-based studies at sea, should be the common practice. Aerial surveillance to get a rapid idea of seabird distribution and ship-based surveys to study ecological aspects and species composition in more detail.