Identification of marsh terns in juvenile and winter plumages

The three marsh terns, Whiskered Chlidonias hybridus, Black C. niger and White-winged Black C. leucopterus, were for a long time considered very difficult to tell apart in juvenile and winter plumages. Williamson (1960) pointed out a number of distinguishing features, since when a few additional characters have been discovered, and most of the important field-marks ar

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