A bird in its second year of life. This is defined as January 1st of the next year. Thus, if a bird is hatched and banded with its year of birth band on Dec. 7, it will still be considered as a yearling for purposes of racing or show come January 1 of the next year. Some breeds do not use the yearling terminology and consider all birds simply Old Birds from the second year on.
A horse which is one year old. January 1 after the year of the birth of a foal is the birthday for all thoroughbred horses. On January 1, a foal becomes a yearling, and on the following January1, it becomes a two-year-old, etc.