The Soft-plumaged Petrel is a gadfly petrel that occurs widely across the southern oceans and exhibits plumage polymorphism. Palebellied individuals make up the vast majority of the species, while dark individuals are relatively rare. Intermediate forms are rarer still and, according to some authors, known only from museum specimens. We describe a number of at-sea records of intermediate-plumaged individuals seen off southwest Western Australia, including a previously undocumented streaked variant. Our observations indicate that plumage polymorphism within the species covers a continuous spectrum of variation between typical pale and wholly dark individuals.
Keywords: Pterodroma mollis, Procellariidae, plumage polymorphism, Indian Ocean, Western Australia