The tune Abby referred to would be An Alarc'h (The Swan); it's the melody of a Breton song (first published in 1839) and was fitted to Twa Corbies some time in the 1960s: opinions differ as to by whom.  It's mentioned in the notes for one of the versions on the DT (TWA CORBIES 2), but the midi there is actually a different tune.

Malcolm