I expect the connection must be the stanza about If I were a blackbird with a bottle of gin, I'd follow the vessel my love's sailing in, and in the top rigging I'd there build my nest, and I'd fly down the cleavage of her lily-white breast. Well, ok, I don't remember the exact words, but you know what I mean, and a similar stanza shows up in a number of versions of Pretty Saro. Trouble is, it shows up in The Prisoner's Song and a number of others. This is a fine example of floating lyric.

Stephen