Gregory The Pigeon/Chicken by Valerie Olson

This book is based on a true story about a baby pigeon who has been separated from his mother and is now an orphan. Three children find him while playing at their great grandmother's house. They convince their grandma Val to take him home and care for him until he is old enough to fly off on his own. The baby pigeon bonds with the chickens next door to his pen by listening to them cluck & cackle all day.
They become life time friends.