Before the events of "How to Pick Your Dragon", Whirlwing was attacked by wild boars. He rested in a cave with an injured wing, and was fed by Thornado. He was shown to be frightened at Stoick's, Hiccup's, and Toothless's arrival, and even more so (understandably) when the wild boars came to attack him, but he was defended ferociously by Thornado and Stoick, who saved him from the boars. Stoick gained Thornado's trust by helping Whirlwing. The gang then proceeded to bring him to Gobber's shop to repair his injured wings.
Whirlwing is a light purple Thunderdrum with small white dots on its wings. Whirlwing's wing has large holes in it as a result of a wild boar attack. As a result, he now wears a dark brown cast around his wings permanently to help him fly.