Happy birthday, Britney, via YouTube.

Britney Spears kicked off the circus over "Circus" -- her sixth album, out today -- by showing up on ABC's "Good Morning America" for two reasons:

1. To celebrate her 27th birthday -- which "GMA" did by foisting a giant, inedible-looking cake on her and including pre-taped birthday wishes from celebrities Hugh Jackman, Reese Witherspoon and Taylor Swift.

2. To perform two songs from the new album, and announce her new tour coming next spring. Opening for her will be: the Pussycat Dolls.

Watch the performances after the jump ...