The wing of a juvenile is used for flying. The wing of the breeding adult is degenerate and used only for balance and in swimming underwater.
The long-necked dipper, Apterocinclus longinuchus, is a semiaquatic, partly flightless dipper, descended from the white-throated dipper, living near the temperate rivers of Europe.
Although there are many examples of flightless birds in the Posthomic period, the long-necked dipper is the only bird that spends part of its life with the capacity for flight and the rest flightless. During its early life the bird develops wings in the normal way, but once it has migrated away from its natal nesting site it becomes totally earthbound and pursues a purely terrestrial/semiaquatic existence. Its wings, now no longer necessary, lose their power and gradually atrophy.