Windwalkers change quite a bit as they age. Infant Windwalkers are covered with both fur and feathers, and are a bit of an ugly ducking.
|“||A newborn Windwalker is a rather extraordinary ball of feathers and fur and looks remarkably like a cross-eyed duckling mixed with an anxious wolf cub.||”|
|— The Incomplete Book of Dragons|
When young, the fur slows the dragon down and its ankles and wing joints are wobbly and bendy. However, as it grows the Windwalker slowly loses the fur and grows more sleek, and its flying ability improves as its joints firm up. If referencing the cover of How to Steal a Dragon's Sword, Windwalkers seem to take on a somewhat crocodilian appearance as they age.
At young age, Windwalkers have larger eyes and ears, small horns, 5 curved claws on each foot, and small protruding saber teeth. They are covered with both fur and feathers, and are a bit of an ugly ducking. As an adolescent the Windwalker begins to lose the fur and grow more sleek. It has not yet mastered flying, but still can carry a person and move swiftly on the ground. As an adult, the Windwalker grows a longer neck, darker scales, wickedly sharp, curved claws, and its maw now resembles that of a crocodile, with many of its teeth showing. The nose horn grows longer and its ears are smaller than when it was young. It can now seat 3 people whereas it used to have slight trouble carrying one. The Windwalker is truly impressive on maturation.
According to The Incomplete Book of Dragons, Windwalkers form a chrysalis at the age of seventeen years and emerge in six to seven months. The reader is left wondering what magnificent form the Windwalker has taken after this transformation. Because of this development timeline and the fact that Hiccup's Windwalker has not yet reached Chrysalis stage, it would seem Hiccup and his Windwalker are roughly the same age—early to mid-teens—during the Book series.
Windwalkers are one of the few dragons able to fly into the thin upper atmosphere, and as an older adolescent can almost match a Silver Phantom in flight. As a mid-aged teenager, Hiccup's Windwalker "had turned into one of the swiftest, most maneuverable dragons in the Archipelago."
Windwalkers have excellent hearing and sight. Their nictitating membranes (third eye-lids) are transparent, allowing the dragon eye protection but not compromising sight. They are able to speak Dragonese, though Hiccup's Windwalker is portrayed as mute. The Incomplete Book of Dragons also indicates that a Windwalker can produce either electricity or lightning bolts.
Windwalkers are faithful and fast, siding with humans during the Dragon Rebellion.
Hiccup's Windwalker transports Hiccup to Berserker Island, where he is captured.
Book 9 continues the appearance of Hiccup's Windwalker.
Book 10 shows Hiccup's Windwalker figuring into the action of the story.
Hiccup's Windwalker continues to stay by Hiccup's side in this final book.
The life cycle of the Windwalker is discussed in this reference book. THe Windwalker also appears in the 'Dragon Key' at the back of the book.
- Some fans speculate that Toothless from the HTTYD Franchise is based partially on Hiccup's Windwalker. Similarities include: extreme loyalty, about the same ages, black color, Hiccup's "riding" dragon, and a superb flyer.
- There is a fan theory suggesting that after the chrysalis stage, the Windwalker will become a Silver Phantom, but this has not been confirmed.