UNUSUAL PATTERNS OF INCOMPLETE PRIMARY MOLT IN LAYSAN AND BLACK-FOOTED ALBATROSSES

Laysan and Black-footed Albatrosses show a bidirectional pattern of incomplete molt in their primaries which has never before been described for any bird. Juveniles molting their flight feathers for the first time replace only their distal three or four primaries. In older birds the ten primaries are divided at their mid-point into two series, each with an independent set of rules for replacement. Unlike most other birds, the primaries of the two series are replaced in opposite directions, with molt proceeding toward the wing tip in the outer series and toward the body in the inner series. The outermost feathers of the distal series are replaced every year without fail; the time available to molt determines how many feathers of this series are replaced. In the inner series, feather replacement occurs only every second to third year. When molt does occur in the inner series it is normally incomplete, and it proceeds in a wraparound pattern which assures that the oldest and most worn feathers are always the first to be replaced.