Madison Beer Sizzles in Feathery Outfit for Her 21st Birthday

Madison Beer ruffled her own feathers on her 21st birthday ... and it was one helluva view.

The singer celebrated her big 2-1 Thursday night in WeHo in front of a star-studded crowd at Delilah nightclub. All eyes were on Madison ... she slayed in a baby blue, bejeweled, carnival-themed costume.

Madison had some stiff competition though in the attention department ... as in the birthday cake.

Baby blue seemed to be the color of the night as Hailey Bieber went chic business with high-knee leather boots. Hailey's hubby had a big hand in practically launching Madison's music career. Remember, it was Justin who 8 years ago tweeted a YouTube video showing then 13-year-old Madison belting out Etta James' "At Last."

The rest is history.