Birdfolk

(Small and Medium) Exotic ancestry.

Birdfolk find sanctuary not in stone or chains, but within the boundless expanse of the sky. However, the gift of flight comes at a cost—hollow bones, and commensurate frailty.

Hollow Bones. You have a fly Speed as long as you are wearing armor no heavier than Leather. Crits against you are Vicious (the attacker rolls 1 additional die). Forced movement moves you twice as far.

From Core Rules