In the third edition of the Field Guide (1974) the 'white patch in the wing-pit' of the Storm Petrel Hydrobates pelagicus is given as a field identification mark, distinguishing the species from both Wilson's Petrel Oceanites oceanicus and Leach's Petrel Oceanodroma leucorhoa. This character was mentioned at least as long ago as 1928 in Birds of the Ocean by W. B. Alexander, as well as in The Han

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