A comparison of the maturation rates of the primaries of redheads (Aythya americana) hatched very early with those hatched very late was made in the 1961 season. Primaries of the early-hatched birds emerged when the birds were 36-38 days old, those of the late-hatched birds when they were 7-10 days younger. This difference was also found in the age at first flight and the age at eventual maturation of all primaries. Primaries of late-hatched birds were significantly shorter in length when mature than were the primaries of early-hatched birds.
Additional publication details
Development and maturation of primary feathers of redhead ducklings