bird is a quarter circle forward motion into light attack. you can cancel into it from most any other move (which is typically the case for any move that is a motion input). you'll want to start down, roll to down-forward, then forward, then press the light-attack button.
the card input that shows the move is showing a little arc along the down and forward inputs
there isn't anything in the game at the moment that gives a good rundown on how motion inputs work, sorry