Wilson's - Oceanites oceanicus Galapagos' - Oceanodroma tethys Graceful - Oceanites gracilis Size is mainly when two species are seen together. However, the first three species are considerably larger than the last two and with a little practice one.should be able to tell these two groups apart when only one bird is present. II. Tail A. 1. Forked Leach's 2. vs. Slightly forked or not forked Wilson's, Harcourt's, Graceful, Galapagos B. Amount of white in tail vs. amount of black 1. Black much greater than white Graceful Storm Petrel 2. White much greater than black Galapagos Storm Petrel These two species are separable from the other three by this character alone. 3. White and black about equal Wilson's Storm Petrel Harcourt's Storm Petrel 4. White slightly less than black, usually with black line through white rump Leach's Storm Petrel As far as this character goes, the last three species are very similar. It is necessary therefore to use the forked tail of the Leach's to distinguish it from the other two species. Wilson's and Harcourt's Storm Petrels are the hardest two species to