Woah! It looks like Happy Birthday might not actually be under copyright.
"Happy Birthday to You" is the best-known and most frequently sung song in the world. Many – including Justice Breyer in his dissent in Eldred v. Ashcroft – have portrayed it as an unoriginal work that is hardly worthy of copyright protection, but nonetheless remains under copyright. Yet close historical scrutiny reveals both of those assumptions to be false. The song that became "Happy Birthday to You," originally written with different lyrics as "Good Morning to All," was the product of intense creative labor, undertaken with copyright protection in mind. However, it is almost certainly no longer under copyright, due to a lack of evidence about who wrote the words; defective copyright notice; and a failure to file a proper renewal application.