Remsen, J.V. 1977 Galapagos Storm Petrel Oceanodroma tethys Ashys. The Wilsons Storm Petrel can be eliminated by the following characteristics: (1) body length and wingspan very similar to Ashy (not obviously smaller); (2) although white is more extensive than on Leach's or Harcourt's, the tail is still all black, and so there is a significant area of black posterior to the white - as much black as there is white; (3) secondaries are conspicuously edged white - this was seen today on our Wilson's (lacking in Galapagos); (4) black of lower back protrudes into white of rump in an oval pattern (cut straight across in Galapagos); (5) long legs of Wilson's protrude beyond tail and are frequently used to patter water (this behavior was noted today once on a Wilson's but not on the Galapagos); (6) today the Wilson's all looked very black and white, blacker than either Ashy or Black - the Galapagos looked sootier or grayer - it didn't give that startling black and white contrast shown by Wilson's; also the white of the tail did not appear as bright and clean. (7) Wilson's tail appears broader with rounded corners in the field (straight-sided rectangle in Galapagos). Illustrations of Galapagos Storm Petrel accentuate the wedge shape of the rump, white patch, but as can be seen from museum specimens (see my report to CFO Rarities Comm), the shape is variable, depending on the arrangement of the uppertail coverts [the white is all on lengthened uppertail coverts, not the tail itself]. This bird definitely had a straight rather than pointed posterior border of the white patch.