diagnostics
32-37 cm, 280-320 g. A small-sized gadfly petrel with white undersides and blue-grey upperparts, with a distinctive, prion-like dark M-shaped marking across the wings and back. Sexes alike. Forehead grizzled white with grey-brown crown. Blackish patch around eye with white lores. Nape, mantle and upper back grey. Rump and upper tail coverts paler grey. Inner upperwing coverts medium to pale grey. Remainder of upperwing coverts, outer primaries and lower back dark grey. Inner primaries, secondaries, and outer grey coverts medium grey. Underwing dark grey with exception of whitish inner marginal coverts. Underparts white, with grey band across upper breast. Flanks washed pale grey. Bill black although some birds show white or pale grey band at base of maxillary. Eyes dark brown. Legs and bases of the toes and webs pink; remainder of feet blackish. Polymorphism occurs, with birds showing uniformly dark plumage affecting =1% of the population (Ryan 2005).
