How long does a song's copyright last?

I was in Wendy's today, listening to fake pop songs over their internal sound systems. Those songs sound like the originals, but they aren't, and it got me wondering: how long does a song's copyright last?

I knew that "happy birthday" was copyrighted, as odd as that sounds, but I didn't know the history behind it. The song was written by a kindergarten teacher in 1893 (who knew they even had kindergarten then). The original words were "good morning" rather than "happy birthday", but the song wasn't protected by copyright until 1935, when one one of the sisters involved filed a lawsuit to prevent its unlawful use by other musicians, and in other forms of entertainment. In the US copyright law now protects a song for 75 years after publication, so it will still be some time until Happy Birthday is in the public domain, if it ever will be. (I wonder how much you have to pay to use it in a movie/tv show now?). In Canada, copyright last for 50 years after the death of the creator of the piece.


http://www.snopes.com/music/songs/birthday.asp
http://www.media-awareness.ca/english/resources/legislation/canadian_law/federal/copyright_act/cdn_copyright_ov.cfm