BIRDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 135 



Such flocks were a usual sight and to their activities may be at- 

 tributed the comparative freedom of this region from the plagues 

 of locusts that are frequently so destructive elsewhere. The useful 

 habits of these gulls are recognized by many farmers, who object to 

 hunters who kill the birds, an attitude that may be followed with 

 great advantage in other regions. 



Xear San Vicente on January 31 I found brown-headed gulls com- 

 mon near the Laguna Castillos where I saw several individuals sick 

 or dead from alkali poisoning. This gull was common near the 

 large lakes at Guamini, Buenos Aires, from March 3 to 8, and was 

 observed in abundance in the marshy region below Cafiuelas. At 

 this season adult birds were ragged and disreputable as they were 

 in molt. In the majority the body was clothed in winter plumage, 

 but wing and tail feathers, more notably the outer primaries, were 

 still in process of renewal. Adult and immature individuals, gath- 

 ered along the lake shore in flocks that contained as high as 100 

 individuals, were wary as they were shot by hunters at every op- 

 portunity. A thousand birds or more were seen daily. Flocks fre- 

 quently passed out to feed in the pastures and were observed fol- 

 lowing plowmen at work in the fields to feed in the freshly turned 

 furrows. 



No gulls were observed during my work in the Chaco. 



This species is known in Argentina simply as gaviota. 



LARUS CIRROCEPHALUS Vieillot 



Larus cirrocephahis Vieillot, Nouv. Diet. Hist. Nat, vol. 21, 1S18, p. 502. 

 (Brazil.) 



The gray-hooded gull was observed only at the Estancia Los 

 Yngleses, near Lavalle, Buenos Aires, from November 1 to 10, 1920, 

 and at the mouth of the Rio Ajo in the same vicinity on November 

 15. An adult female was taken November 1, and an adult male, 

 preserved as a skeleton, on November 10. After minute comparison 

 of four of these gulls from Buenos Aires, with a series of 27 from 

 Africa, all adult, I may only substantiate the observations of others 

 and state that, anomalous as it may seem, there is no apparent dif- 

 ference between birds from the two localities. Those from South 

 America seem very slightly larger but in the series at hand the 

 distinction is too slight to be reliable. One may well ponder on 

 the conditions that have brought about such a remarkable dis- 

 tribution in this species and on the length of time that the two 

 groups of individuals have been separated. 



The adult bird is easily distinguished from the brown-hooded gull 

 that inhabits the same region by the much lighter head, a difference 

 that may be detected in a favorable light at a considerable distance. 

 The note of cirrocephalus is a strange caw caw, similar to that of a 



