Scientists have found that while canaries are excellent imitators while very young, once they hit puberty, they drop any "false" songs they have learned and sing according to ridged rules.[1] They are as yet unsure of the birds sound the same to each other, that is, if females will mate with the males who learned other songs while young, as readily, more readily, or less readily than "normal" canaries. They are correct, that this is fascinating. Why would canaries have this ability to learn other songs while young, only to drop it later? Why would they have the ability to learn at all when they do not seem to need the example to learn the "correct" songs?
[1] http://news.bbc.co.uk/2/hi/science/nature/4544777.stm