Erica didn't do a terribly good editorial job there, either, though in fairness to her the mis-spelling was originally Dick Gaughan's; she lifted the lyric from his website without acknowledgement. In the original, the bird is 'martlet', an alternative form of 'martin'.

It just goes to show how important it is to credit sources when quoting lyrics etc. Quite apart from anything else, giving due credit to your source means that you can also blame them (in part) if it turns out to be wrong. The picture of a flying weasel is engaging, though perhaps also a little scary, come to think of it.