Life history implications of complete and incomplete primary molts in Pelagic Cormorants

We describe the rules of primary flight-feather replacement for Pelagic Cor morants (Phalacrocorax pelagicus), and contrast the completeness of primary replacement in individuals from Asia and North America. In adult Pelagic C ormorants primary replacement is stepwise, with multiple waves of molt, eac h initiated at the innermost primary (Pl), proceeding simultaneously toward the tip of the wing. Shugart and Rohwer's (1996) ontogenetic model for gen erating and maintaining stepwise primary replacement depended upon incomple te molts. In each new episode of molt, waves of primary replacement were th ought to be initiated at PI and at each arrested wave that had failed to re place all old feathers in the preceding molt. Because most adult Pelagic Co rmorants from North America completely replace their primaries but maintain stepwise primary molts, the latter assumption must be relaxed, In contrast to the present-day situation in North America, Pelagic Cormorants from nor theastern Asia have incomplete molts of their primaries, and may be forced to skip breeding in some years to clear their wings of overworn primaries. Young birds from Asia start the replacement of their juvenile primaries lat er than North American birds and replace more feathers simultaneously.