1917 BIRDS OF THE SOUTHERN CALIFORNIA ISLANDS 
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BT. Oceanodroma socorroensis ©. H. Townsend 
Socorro PETREL 
Oceanodroma socorroensis (1) Townsend, Proc. U, S. Nat. Mus., x1, 1890, p. 134. (2) 
Anthony, Auk, x1, 1895, p. 387. (3) A. O. U. Committee, Auk, xiv, 1897, p. 117. (4) 
Anthony, Auk, xv, 1898, p. 140. (5) Davie, Nests & Eggs N. Am. Birds, 5th ed., 1898, 
p. 58. (6) Grinnell, Pac. Coast Avif., 3, 1902, p. 16. (7) Grinnell and Daggett, Auk, 
xx, 1903, pp. 31, 37. (8) Reed, N. Am. Birds’ Eggs, 1904, p. 54. (9) Osburn, Condor, 
xi, 1911, p. 31. (12) Willett, Pac. Coast Avif., 7, 1912, p. 20. (173) van Rossem, 
Condor, xvi, 1915, p. 76. (14) Grinnell, Pac. Coast Avif., 11, 1915, p. 28. 
O[ceanodroma]. socorroensis (15) Coues, Key N. Am. Birds, 5th ed., 1903, p. 1044. 
Oceanodroma monorhis (16) Godman, Monog. Petrels, 1, 1907, p. 33. 
Breeds commonly on the smallest island of Los Coronados group. A. W. An- 
thony (4) says that on the Coronados, April 24, 1896, he found a number of 
nearly finished burrows and one bird. June 12, 1914, D. R. Dickey (MS) found 
several pairs of birds but no eggs. It will therefore be seen that socorroensis be- 
2ins preparing the burrows nearly two months before laying. This species breeds 
only in burrows which are excavated by the birds themselves, and for this rea- 
son, to be looked for only where there is a deposit of ight loam, sometimes over- 
erown with a dense mat of bushes. The tunnels are usually about two feet long, 
enlarged at the end. In the majority of cases they turn either to the right or 
left a few inches from the entrance, which latter seems unusually small for the 
size of the bird and is more than twice as wide as high. Occasionally the egg is 
laid on the bare ground, but usually there is a flimsy platform of any bits of 
twigs and rootlets that may be handy. The egg has a wreath of faint lavender 
dots and tracings about the larger end. The average measurement of forty-two 
which I have had in my possession, is 1.18x.89 inches, and the extremes are 1.09 
to 1.23 in length, and .82 to .97 in diameter. I believe that the nesting dates of 
the Black and Socorro petrels will run about the same. In 1910 I did not find an 
egg of the latter until June 22, while those of the former were taken a week pre- 
vious. In 1913 A. van Rossem and I found the opposite to hold good, for during 
the latter half of June slightly incubated eggs of socorroensis was the rule, while 
those of melania were still fresh. 
Unlike their larger relative, Socorro Petrels but rarely vomit oil when re- 
moved from the nest, but will often do so immediately after having been released 
from the hand. This oil is substantially the same as that secreted by melania, 
but sometimes contains flakes of whitish mucous matter, in addition to a little 
green slime and a tiny rock lobster or two. Some birds taken by A. van Rossem 
(MS) in 1914, contained what appeared to be young squid about an inch long. 
In the hand one is impressed by the frailty and apparent weakness of these birds. 
When released they launch forth in an uncertain manner, twisting and turning 
in their nighthawk-like flight. If placed upon the ground they poke confusedly 
about among the bushes. 
F. Godman (16) considers this species and Oceanodroma monorhis of the 
western Pacific, to be indistinguishable, although the type of the latter is of a 
lighter gray on the head and throat than is the former. Dr. Hartert (MS) of 
