As you are hurt, you dissipate into a host of sparrows, flying to re-form farther away.

Daily   ✦     Polymorph, Primal
Immediate Reaction      Personal

Trigger: You are damaged by an attack

Effect: You assume the form of a cloud of flying sparrows until the start of your next turn, and you fly your speed without provoking opportunity attacks. While in this form, you are insubstantial, you can't attack, and you can't pick up or manipulate objects. If you are still airborne at the start of your turn, you land without taking falling damage.

Published in Player's Handbook 3, page(s) 123.