Tonk and the Battle of the 200 by Jon Mann
Series: The Adventures of Tonk #1
One day he hears of a magical flying squirrel whose coat is as white as snow. She is held captive in a place called "The San Diego Zoo", and Tonk knows his time has come.
Leaving his family behind, he sets forth on a dangerous journey to rescue the legendary squirrel with the hope that he, too, can learn the secret of flight. Along the way he makes friends with Bogey, a crusty old jackrabbit: El Curador, a Mexican museum mouse; and Pockets, an alarmingly awkward pelican. Together they forge a trail across a treacherous urban landscape to the mysterious place where the creature has been imprisoned against her will.
Once there, Tonk and his brave friends wage war against the enemies who have imprisoned the white squirrel. In doing so, Tonk becomes much more than the simple creature he is -- he becomes a hero.
After all, who says you have to be big to make a difference?