Harcourt Storm Petrel 
(Oceanodroma castro) 
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I ajn Quite sure I saw this species Trom about 5 S to 10 S« 
Due to the difficulty in separating this from Leach Storm Petrel, 
most birds were logged as Leach or next most similar species. 
The four individuals logged as llarcourt definitely lacked the dark^ 
feathers in the middle of the rump patch. Other that this T could find 
no difference in pattern, size, or behavior from Leach Storm Petrel. 
I must also state that these birds were not Oceanodroma tethys , or 
Oceanites oceanicus and were recorded as Oceanodroma castro by the 
elimination of the above two species. 
Leach Storm Petrel 
( Oceanodroma leucorhoa ) 
V^hite-rumped Storm~Petrel sp. 
A very abundant species, perhaps one of the'most abundant birds 
in the world. Hecorded in every section of the cruise, being second 
only to Sooty Terns in total number of individuals. Large populations 
were found about 25<^N, 13^N, lO^N, and throughout the equatorial doldrums. 
After crossing the doldrums, Leach became rarer until Ihey finally 
disappeared at 17^S. 
Under good conditions two forms can be recognized in the field. 
The northern form, Oceanodroma 1. leucorhoa , appears larger, darker, and 
has more white in the rump. The southern form which includes about 
three sub-species, is smaller, browner, and the amount of white in the 
rump varies considerably. Both forms were observed in all sections of 
the cruise track, but I think the northern form was dominant at 25 N, and 
the southern birds at 13®N, lO^N, and all of area ^’C”. The large 
populations along the doldiwis contained both forms of unknown ratios. 
All sub-species inter-mix freely at sea, and at least two races were 
collected from the same flock. The southern birds were in very worn 
plumage especially on head and throat while the northern birds were 
not. 
Ashy Petrel 
( Oceanodroma homochroa ) 
This species evidently occurs south of its breeding range at 
least to the Revilla-Gigedo Islands in non-breeding season. It ^ 
was observed in flocks of light and dark-rumped Leach and was distinguished 
b\y its smaller, chunkier appearance, fluttering flight, and light 
grey under-wing converts. 
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