164 BULLETIN 121, UNITED STATES NATIONAL MUSEUM. 



the hand in and lifting up the top soil. The terminal chambers were larger 

 here than in the burrows among the rock fragments. Often two burrows crossed 

 or united, but always the occupants were in separate terminal cavities. The 

 shortest burrow did not exceed twelve inches in length, the first lifting up of 

 the top disclosing a Socorro petrel and egg. The longest observed was in 

 stoney ground, and zigzagged about so that in all its windings it extended fully 

 six feet. The nest cavities sometimes showed a sparse flooring of fine twigs and 

 grass, but just as often they were altogether bare of any lining. 



Mr. A. W. Anthony (1896«) found both the black and the Socorro 

 petrels breeding on the San Benito Islands, near Cerros Island off 

 the west coast of Lower California, but, as his notes have been freely 

 quoted under the former species, I shall not repeat them here. 

 There is some doubt as to whether the Socorro petrel breeds at all 

 on the island for which it was named and on which Mr. Townsend 

 discovered it. Mr. Kaeding (1905) observes: 



It is interesting to note in this connection that so far as we were able to 

 ascertain, there are no sea birds nesting on Socorro Island at all, with the 

 exception of the terns nesting on the outlying rocks. Mr. Townsend found 

 burrows that he judged would be occupied later by petrels, but I am con- 

 strained to believe that these were the burrows of the land crabs, which swarm 

 over the island. These crabs are so voracious and bold that it would hardly 

 be possible for even a shearwater to withstand their attacks, and this is 

 probably the reason why, although thousands of shearwaters nest on San 

 Benedicte thirty miles away, none nest on Socorro, there being very few crabs 

 on San Benedicte. 



Eggs. — The single egg of the Socorro petrel is similar to the eggs 

 of other small petrels ; the shape is between oval and elliptical oval, 

 generally nearer the former ; the shell is smooth and lusterless. The 

 color is dull dead white ; Mr. Howell says that it " is sometimes pure 

 white, but more often has a wreath of faint lavender dots and trac- 

 ings about the larger end"; Mr. Anthony (1896&) refers to it as 

 " usually freckled with reddish spots in a more or less complete ring 

 about the larger end." The measurements of 18 eggs, in various 

 collections, average 30.8 by 23.2 millimeters; the eggs showing the 

 four extremes measure 34 by 24, 32 by 24, 29 by 22.5, and 30 by 22 

 millimeters. 



Before the egg is laid both parents occupy the burrow. Incuba- 

 tion is performed by both sexes alternately, and after a fcAv days the 

 young is left in the nest alone during the day. 



Plumages. — The downy young has the chin and throat naked, but 

 is otherwise covered with long, soft down of a uniform, " deep mouse- 

 gray " color. The young bird is nearly fully grown before any 

 plumage appears; the wing feathers are the first to grow, and then 

 the tail, both of which are complete before the contour feathers are 

 acquired. The first plumage assumed seems to be indistinguishable 

 from that of the adult. Messrs. Grinnell and Daggett (1903) refer 



