OCEANODEOMA. 431 



3. Oceanodroma socorroensis. 



Oeeanodroma socorroensis. Towns. Pr. U. S. Nat. Mus. xiii. p. 134 ' ; Salv. Cat. Birds Brit. Mus. 



XXV. p. 352'; Anthony, Auk, 1895, p. 387'; 1898, p. 38'; Gates, Cat. Eggs Brit. Mus. i. 



p. 149, t. 11. fig. 6 '. 

 Oceanodroma townsendi (nee Eidgw.), Anthony, Auk, 1894, p. 321 '. 



0. melanice Bimilis, eed minor, plaga brunnea alari pauUo magis extensa, tectricibus medianis anticis quoque 

 brunnescentibus ; supracaudalibus lateralibus s^pius cinerascentibua, interdum albidis ; subalaribus 

 rufescenti-brunneis, marginalibus nigerrimis : rostro et pedibus nigris. Long, tota circa 7-8, aljB 5-9, 

 caudse 2-95, culm. 0*61, tarsi 0-8. 



$ mari similis. Long, tota 7-5, alse 5-85. (Descr. maris et femin^ ex San Benito Is. Mus. Brit.) 



Hab. Calipoknia, as far north as the Santa Barbara Channel, San Diego 3, San 

 Benito Is. (Anthony^) ; Eevillagigedo Is., Socorro I. {Townsend ^ ^). 



This species is described as similar to 0. homochroa, but with the wings longer, and 

 the tail shorter and less deeply forked, the tarsus and toes shorter, the sides of the 

 rump whitish, and with no white on the under surface of the wings. The dimensions 

 are given as follows: — Wing 5-50, tail 2-75 (forked for 0-50), culmen 0-55, tarsi and 

 toes 0-85 1. 



Only one specimen was secured and a few others seen, but Mr. Townsend found the 

 hills at the western end of Socorro Island literally honeycombed with the burrows of 

 some creature which he believed to be this Petrel. The most diligent search did not 

 reveal any small mammal on the island, and lizards could not have excavated these 

 burrows ^. 



This is a smaller bird than 0. melania, which otherwise it closely resembles. The 

 light patches of whitish or grey appear to be by no means a constant character, as 

 Mr. Anthony has already remarked. The type-specimen has whitish patches on the 

 sides of the rump [i. e. the lateral upper tail-coverts), but in over one hundred skins 

 he has found only about 3 per cent, so marked. A few were nearly as white on the 

 rump as 0. leucorrhoa ; but the largest part of the series, fully 95 per cent., had 

 sooty-black coverts above and below. Two or more species, he adds, might be 

 made, but unfortunately the light-rumped birds are found in the same burrows with 

 the dark ones. 



Specimens of 0. socorroensis have also been obtained off San Diego, California, so 

 that the species is now included in the avifauna of the United States ^. Mr. Anthony 

 has also found it nesting on the San Benito Islands, between Guadalupe I. and the 

 Cerros Is., and has presented specimens of both birds and eggs to the British Museum. 

 He says that it is found on the open sea, in small companies of not more than three 

 together ®. 



The eggs are elliptical in shape, white, marked with pink specks and dots at the 

 broader end. In one egg these form a cap, in the other an indistinct zone, a few 

 specks being also scattered over the shell 5. 



