~i Q Q I n each of last month's mystery photographs (plates 36 & 37, reA O O peated here), the bulky bird widi the white wing-flashes is die same individual. like the aumor, readers will be relieved to learn that diis is the mystery bird, and mat they were not expected to identify die small, dark shapes, which are storm-petrels (Hydrobatidae).In combination, the robust structure and those conspicuous white bases to die primaries, botii above and below, point directiy to one of die larger skuas Stercorarius, of which two species have occurred in the Western Palearctic: the familiar Great Skua S. skua and die rare and problematical Soutii Polar Skua S. maccormicki. The smaller Arctic Skua S. parasiticus and Long-tailed Skua S. longicaudus, with their obviously more rakish and streamlined build, can be discounted immediately, whilst both tiiey and die intermediate Pomarine Skua S. pomarinus do not possess such striking wing-flashes as the mystery bird, particularly on the upperwings. Even in direct comparison, Great and South Polar Skuas cannot be separated in die field on size or on any structural character (see Brit. Birds 86: 176177). Furthermore, bare-part coloration is of no assistance in the identification process, and neither is the extremely variable extent of the white on die base of die primaries. Ignoring these features, die mystery skua is most notable for its pale head widi a dark area around die eye, its even paler nape, and itsgenerally pale underbody which contrasts against very dark axillaries and underwing-coverts.