The page Jon linked (thanks, Jon) has a difficult time with the word 'carnal,' saying, 'The word would presumably be a borrowing from the French corneille.'

I suspect it's simply a dialect form for 'cardinal,' another kind of bird. I think it would be easy for people who do not read or write to lose track of the 'd' in the middle of 'cardinal.'

Of course,it would have been simpler if the person who collected the song had asked what it meant and kept a record!