THE BIRDS OF CLIPPERTON AND COCOS ISLANDS 513 



The species was observed fishing at sea, three hundred miles from 

 the island, and it is probable that the birds in pursuit of food, daily 

 travel more than a hundred miles from their breeding ground. 



The eggs are covered with a dull white outer limy coating. The 

 shell beneath this is pale greenish, showing where the former is 

 scraped off. In shape they are regularly ovate to elongate ovate. 

 Size, 62 X 43 to 72 X 47 mm. 



SULA BREWSTERI Goss. 



Sula bre-custeri Goss,, Auk, v, p. 242, 1888 (San Pedro Matir Island). — Ogilvie- 

 Grant, Cat. Birds Brit. Mus., xxvi, p. 440, 1898. 



Range. — Pacific coast of Mexico and Central America, Rivilla- 

 gigido Archipelago, Cocos Island. 



Adult jMale. — Cat. No. 5220, Stanford University Museum, from 

 Cocos Island, July 3, 1899. Feathers of heiid just back of bare space 

 very pale, nearly pure white above, almost immediately, however, 

 darkening into grayish and then into brownish-gray, passing from this 

 through grayish-brown on the hind neck, sides of head and throat into 

 dark sooty-brown on the back, upper surface of wings, tail and upper 

 breast, the brown darkest on under surface of the primaries. Lower 

 breast and belly pure white. Under wing coverts of secondaries gray 

 and white. Median lower tail coverts white, the lateral ones brown. 

 Bill pale horn-biown. Feet light pea-green. 



Adult Female. — Cat. No. 51S7, Stanford University Museum, from 

 Cocos Island, July 3, 1899. — Same as the male but the brown color of 

 back and upper breast extending forward uniformly over the neck and 

 head to the bare skin about base of bill. Gular-sac and base of bill 

 pea-green, spot before eye slate-blue. Feet light yellowish ; claws 

 horn-blue. 



Immature Male. — Cat. No. 3845, Stanford University Museum, 

 from Cocos Island, July 3, 1899. Plain smoky-brown, lighter than 

 the adults. The lower breast and belly with pale grayish edgings to 

 the feathers, giving this region a paler appearance than the other parts. 

 Feathers of top of head, back of neck, back and wing coverts with 

 pale brown edgings. Under wing coverts gray and brown. Bill and 

 gular-sac slate-blue. Feet cream-yellow ; claws horn-blue. Iris 

 white. 



Both males and females are conspicuously darker than Sula nesiotes 

 of Clipperton Island, and the male has much less white on the head 

 and neck. 



We found this species fairly common in July on the rocks and islets 

 about Chatham Bay, Cocos Island. 



