1917 BIRDS OF THE SOUTHERN CALIFORNIA ISLANDS 35 



37. Oceanodroma socorroensis C. H. Townsend 



Socorro Petrel 



Oceanodroma socorroensis (1) Townsend, Proc. U. S. Nat. Mus., xiii, 1890, p. 134. (2) 

 Anthony, Auk, xii, 1895, p. 387. (3) A. O. U. Committee, Auk, xiv, 1897, p. 117. (Ji) 

 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. (.S) Reed, N. Am. Birds' Eggs, 1904, p. 54. (.9) Osburn, Condor, 

 XIII, 1911, p. 31. (12) Willett, Pac. Coast Avif., 7, 1912, p. 20. (13) van Rossem, 

 Condor, xvii, 1915, p. 76. (/-'/) Grinnell, Pac. Coast Avif., 11, 1915, p. 28. 



Olceanodroma], socorroensis (lo) Coues, Key N. Am. Birds, 5th ed., 1903, p. 1044. 



Oceanodroma monorhis (1(>) Godman, Monog. Petrels, i, 1907, p. 33. 



l^reeds commonly on the smallest island of Los Coronados group. A. W. Au- 

 tliony (i) 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- 

 gins 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 light loam, sometimes over- 

 grown with a dense mat of bushes. The tunnels are usually al)Out 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 foi' 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 liaving 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 Oceniiodronia 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 



