Plumage dimorphism in Wedge-tailed Shearwaters Puffinus pacificus in Shark Bay, Western Australia.

Although many Wedge-tailed Shearwaters Puffinus pacificus in northern hemisphere populations have white underparts, almost all members of this species around Australia have uniformly blackish-brown plumage. The exception is Wedge-tailed Shearwaters on islands in Shark Bay, on the central coast of Western Australia, where in 1972 about 20 per cent of an estimated 600 pairs had white breasts. We visited these islands in December 1997 and February 1998 and estimated both the overall population size and proportion of white-phase individuals as unchanged after 25 years. White-phase Wedge-tailed Shearwaters are unknown at much larger colonies north and south of Shark Bay and only recorded at sea within a 200-300 kilometre radius of Shark Bay. This unusual, isolated population and its plumage dimorphism appear stable, but would repay further investigation.

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