Bird banders use an age code that is linked to the calendar year. This code is used by the Canadian Wildlife Service and the United States Fish and Wildlife Service.
U (unknown) is for a bird after the breeding season and before 1 January that cannot be placed in any of the age classes below. After 31 December use AHY.
L (local) is for a young bird incapable of sustained flight. Banders sometimes label these birds as Juv (juvenile), but it is not part of the official code.
HY (hatching year) is for a bird up to and including the 31 December of the calendar year in which it was hatched. It includes birds in juvenile, first winter and first year plumages. Banders sometimes use the label Juv for birds that are clearly in juvenile plumage, but this use is not officially part of the code.
AHY (after hatching year) is for a bird in at least its second calendar year or older. Year of hatch is unknown, but it is at least a SY.
SY (second calendar year) is for birds in their second calendar year from 1 January to 31 December. These birds are known to have hatched in the preceding calendar year.
ASY (after second year) is for a bird in at least its third calendar year. Year of hatch is unknown.
TY (third year) is for a bird known to be in its third calendar year.
ATY (after third year) is for a bird (normally adult) in at least its fourth calendar year. Year of hatch is unknown.