Cuccos are a recurring creature in Zelda games. Despite the fact that they have two wings and two legs, are nearly flightless, peck the ground with their beaks, and cluck, they are not chickens. Link often uses them in the same way people use hang gliders - By holding them above his head and jumping from high locations.
There are very few creatures which appear throughout the entire Zelda timeline. Aside from humans and to an extent Zora, all of them - such as moblins, bubbles, and redeads - are evil demons. Therefore it's probable that cuccos are in fact an evil species, possibly attempting to overrun Hyrule. But few people are on to their machinations.
Cuccos tend to travel in groups. If one was to strike a cucco repeatedly with a sword, or otherwise harm it, perhaps using explosives, it's likely that said cucco would call its friends to aid, and the assailant would be caught in a very dangerous situation. Enraged cuccos have been known to flap their wings hard enough to achieve momentary flight, and dive at people with their beaks; however, very few people have witnessed a cucco attack and lived to tell the tale. In The Legend of Zelda: The Wind Waker, far less lethal pig attacks appear to have taken the place of the Cucco swarm.
Cucco wrangling is a popular minigame.