A little more admitedly unsupported evidence for the crow-scaring song theory.
I've just returned from a folk festival in the Central Victorian (Aus) town where my family have been since the 1840s. The tunes still played by the older musicians are the songs made popular by the American and British minstrels back in the 19th century. It was here that my father learned "Jimmy Crack Corn" well before any of the discussions, mentioned above, about the word "Gimme". We kids, in Australia, growing up in the 1940s never questioned the phrase "Jimmy crack corn and I don't care" we understood that it was about birds cracking and eating corn. One of the versions of this song - (one of the above threads) is in fact all about birds in the cornfield.