Voedsel en fourageergebieden van broedende Zwartkopmeeuwen Larus melanocephalus in Zuidwest-Nederland

The largest NW-European breeding population of Mediterranean Gull is found in the SW-Netherlands (1990 80 pairs, 1991 113 pairs; fig. 1). Most breeding sites in this area are situated on now permanently exposed, former tidal areas which have been recently dammed. Food remnants collected from adults and chicks in various colonies predominantly consisted of earthworms, leather}ackets and beetles (table 1), and suggested mainly terrestrial feeding by the adults. A survey in mid-July of an extensive grassland area in the western part of the province of Noord-Brabant and the adjacent part of Belgium, within 30 km of the most important breeding sites, revealed up to 44 feeding Mediterranean Gulls (fig. 2). They showed a preference for (especially recently mown or recently manured) grasslands on sandy soils (fig. 3). No feeding Mediterranean Gulls were observed on grasslands on clay, which may be an explanation for the fact that only small numbers of Mediterranean Gulls breed in the western part of the Delta area. Although tens of juveniles had already fledged by mid-July 1991, not one was observed feeding on the grasslands. It is suggested that juveniles almost immediately leave for the North Sea coast. This is supported by the sightings of colour-ringed juveniles in France and England within weeks of fledging.