Chickens are domesticated birds mentioned in the How to Train Your Dragon Book series.
Chickens are birds with a poor ability to fly, but are know for their usefulness to humans and the males' vocalizations - the distinct 'cocka-doodle-do'. Chickens originated largely from India and South East Asia from the Red Junglefowl (Gallus gallus). Domestic chickens are actually considered a sub-species of this wild bird (Gallus gallus domesticus). There are some traces of other junglefowl (Genus Gallus) species within some breeds of domestic chicken, including the Grey junglefowl. The Grey junglefowl contributed the genes for yellow skin to domestic chickens, which is absent in Red junglefowl. The unique domestic chicken breed, the South American Aruacana which lays blue and green tinted eggs, is said to trace some ancestry to the Green junglefowl, possible brought over by Polynesian travelers millennia ago.
Chickens are known in both the Book series and in real life for their use as food. Both the eggs and the bird itself are eaten. Additionally, the Book series indicates that books can be purchased by trading it for a "smallish chicken" and 20 oysters, specifically the book How to Train Your Dragon mentioned in How to Train Your Dragon.
A "smallish" chicken is mentioned as part of the cost for the in-universe book, How to Train Your Dragon.
There is also an image of Stoick eating a large meal, and one of the items appear to be whole roast chicken.
Toothless' triumphant cry also sounds like a rooster crowing and is seen saying "cock-a-doodle-doo" on occasion.
|“||He let out the dragon's cry of triumph, which is a bit like a rooster crowing but a lot louder and more self-satisfied||”|
|— Book 1|