Age (Year Class) and Sex Codes
It is difficult to develop a system for coding the age of birds based on "bird years" (breeding season to breeding season). Effective July 1, 1967, a revised system of age codes based upon the calendar year was established. Each time a bird passes December 31, it graduates to the next higher year class. In January, a bird hatched the previous June would be in its second calendar year ("SY"), although it is only seven months old.
The "Year Class" codes used in conjunction with techniques for aging birds will enable banders to record the "Year Class" of some species through the first three calendar years. If age determination is less precise, this system of codes will also enable banders to indicate birds that are "at least 'X' years old" but perhaps older (codes "AHY", "ASY, or "ATY").
For some species the sex can be determined by the plumage of the bird, cloacal exam, body size, blood testing, or other techniques. The sex at banding is reported the same way regardless of technique used to sex the birds.