RENSSEN TA (1981) Freshwater drinking flights of Mute Swans Cygnus olor feeding on a salt lake. LIMOSA 54 (1): 29-30.

Since the closure of the Brouwershavense Gat in 1971 increasing numbers of Mute Swans have been observed moulting and wintering on the salt lake Grevelingen, a former estuary in the southwestern part of the Netherlands where the salt concentration is kept nearly equal to that of the adjacent North Sea. The food of these swans consisted nearly exclusively of Eelgrass Zostera marina. End October--early November 1979 the author saw regularly birds making drinking flights to freshwater pools on the former saltmarshes bordering the lake. Coots showed the same behaviour pattern. Mute Swan Cygnus olor

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