the light phase one from Hawaii or the dark phase population from the 
Line Islands or French Polynesia. This conclusion is inescapable. 
Further work will be necessary to tell which population is from an out¬ 
side area or if in fact both populations are from the west with the 
eastern Pacific birds intermingled with these populations. 
Juan Fernandez Petrel (Pterodroma e^. externa) 
Juan Fernandez Petrels were common only along 105 °W. Earlier in the 
summer Gould found them commonly along the 98°W meridian suggesting a 
westward movement in August. This could correspond with the increase of 
this species in the central Pacific during late summer. It should be 
♦ 
remembered that at the same time they are common in the eastern Pacific 
(August) they are also common in the central Pacific - a range of over 
2000 miles. 
Collared Petrel ( pterodroma leucoptera brevipes) 
Collared Petrels are easily separated from other forms of small 
Pterodroma by the dark underwing border and black cap which extends down 
the neck. 
Hydrobatidae 
In the past, identification of the dark storm petrels with white 
rumps has been difficult.. This is due in part no the fact that on most 
trips only one species is seen, namely Leach's Storm Petrel. 
In t.ns trip most of the species of this group were observed, and after 
watching them in the field and checking study skins I feel that I can 
identify a good many individuals in the field by size and plumage charac¬ 
ter .sties. The following is my identification key to the "white-rumped” 
storm petrels of the central and eastern Pacific. 
I. Size: Largest to smallest 
Leach's - Oceanodroma leucorhoa 
Harccurt's - Oceanodroma castro 
