Evidence for color phase effects on the breeding and life history of Northern Fulmars

About 15% of Northern Fulmars (Fulmarus glacialis) breeding on the Semidi Islands in 1979 had light-phase plumage; the remainder were dark. Fulmars of different plumage types mated indiscriminantly, but the lighter member of a mixed pair was more likely to be male than female. Pairs that included at least one light-phase member had lower breeding success than dark/dark pairs in one of six years. Constancy of breeding site use differed between light/dark and dark/dark pairs, suggesting dark birds skipped more breeding attempts or had lower over-winter survival than light birds. The apparent effect of breeding experience (assessed by site fidelity) on success also differed between pair types. The polymorphism on the Semidi Islands may result from light-phase fulmars immigrating from the Bering Sea, but there is also evidence to suggest it is maintained by balancing selection in a closed population.