I'm amazed how many people on here are trying to find a French link and all manner of complicated theory. The reasn was recorded long ago and is much more simple and logical, As the trick or joke of the song is a suitor at first sending fairly normal gifts then increasingly weird as the song goes on. then a Partidge in a real pear TREE doesn't even fit (by the way the French perdee surely means a pheasant) It is of course a bird cage names a 'PEAR TREE CAGE' a very normal and common gift in Victorian times up to the early 1900's, if anyone remembers the BBC TV show Going For A song, a pear tree cage with mechanical singing bird featured in the opening titles.That is the only correct answer