Crimson Loftwing
The Crimson Loftwing is Link's feathery friend is his mode of transportation when traveling amongst the clouds know as a Loftwing. Link can leap off ledges and call his bird as he falls. Link's bird will swoop right underneath him giving Link a perfect landing spot. Link can use his bird to travel between the various islands in The Sky.
Link's bird seems to have some sort of connection with Zelda's bird, as the two can be seen flying together even when Link and Zelda are not with each other. Link's bird can hold more than one passenger at a time, as Link and Zelda are both riding on the bird simultaneously at one part in the game.
Link's Bird is a rare breed of Loftwing, being bright crimson in color. Link, like all Skyloftian Loftwing riders, befriended his bird as a child or young adolescent. According to Gaepora, Link and his bird possess a bond like no other in Skyloft, as Link was able to fly with ease when he first met his Loftwing (something that even Zelda was jealous of).
Link's Loftwing was stated to be a special bird by the developers, and it's unclear if this is the only trait that makes him special or if there is more to it.