Here's a quote from this link
http://www.copyrightauthority.com/song-copyright.htm :
"
Under the Berne Convention, most countries have a deal where as soon as your song, music or lyrics are written down in a tangiable form -then they are already copyrighted. You don't need to do anything.
"
I think this would include an upload to YouTube.
You can register your copyright, and a google search turns up places that will do this for as little as $5. Registering would presumably give you added protection in the event you are infringed.
However, speaking for myself, the chances that someone might actually make money off of one of my songs is so remote, it's not even worth the $5 to me. If it really turned out to be significant money, a lawyer would probably take the case on contingency. Anything else and I would probably be glad just to have someone cover my songs.