From Zelda Legends Wiki
The Pocket Cucco is the item that starts off the Trading Game for Ocarina of time. By talking to the Cucco Girl in Kakariko Village as adult Link, one obtaines the Pocket Egg; by waiting a day (or using the Sun's Song) the Egg hatches into the Poccet Cucco. The player must use the Cucco to wake up Talon near the entrance of the village. By showing the Pocket Cucco to the Cucco Girl after this, she decides that you're a good Cucco keeper, and entrusts to you the Blue Cucco, Cojiro.