204 PATAGONIAN EXPEDITIONS: ZOOLOGY. 



cut 124.) Immature birds are similar to young of the year, but the mantle 

 is not mottled, and .there is no mottling on the upper wing coverts. The 

 decorations on the primaries increasingly white. 



The size of this bird in connection with the pale grey under wing 

 coverts, will always serve to distinguish it in its various phases of imma- 

 ture dress from its closest allies in this group. 



Geographical Range. — South America, from about 9° South Latitude, 

 on the East Coast, to South Patagonia. On the West Coast from about 

 50° South Latitude northward to probably about 30° South Latitude. 



This gull, which has been frequently confounded with its close ally S. 

 'glancodes, especially in immature plumage, has been found generally both 

 on the coast and the interior of Patagonia. It was not obtained, however, 

 by the Expeditions of Princeton University, and the series of skins in the 

 British Museum of Natural History has been examined as a basis for 

 the above diagnoses. The birds are said to be resident and to breed in the 

 vicinity of Buenos Ayres, in November. Other references to its breeding 

 season are given in the literature cited. 



The British Museum has received two examples of this species from 

 Valle Lago Blanco del Chubut, collected by Mr. J. Koslowsky, one of 

 which is an adult male and has the head, sides of face, chin and throat 

 brown. This specimen was obtained on September 16, 1899. The 

 second example is an immature male with the crown of head, sides of face 

 and throat white — only a trace of brown on the hinder margin of the 

 ear-coverts — this bird was procured on October 24, 1901. 



Buenos Ayres, August 21, 1870. 

 "People in Buenos Ayres are as familiar with the Gaviota [Lams cirrJw- 

 ceplialus) as with the domestic poultry about their houses. It is one of 

 the trio of our commonest species, the other two being the Tern and the 

 Chimango. But these two are exclusively land birds, and to make their 

 acquaintance it is also necessary to go a few miles out of a great crowded 

 city. Not so with the Gaviota, whose white graceful form is not more 

 familiar to the gaucho dwelling far off on the inland plains than to the 

 sailors in every ship that navigates the river Plata, or to the townsmen, 

 who may know it well without ever having left the city's pavement. 



