Sexing and Aging terminology

HY = Hatching Year martin; a nestling or fledgling that was hatched in the current season. Since it is not possible to determine the sex until the first molt, these are often referred to as HY-U, which means Hatching Year - sex Undetermined

SY = Second Year martin; a martin that hatched/fledged in the prior nesting season. These individuals are capable of breeding; SY-M = subadult male;  SY-F = subadult female

ASY = After Second Year martin; often referred to as an adult. ASY-M = adult male; ASY-F = adult female