134 BULLETIN 133, UNITED STATES NATIONAL MUSEUM 



differences other than those that serve to separate species. As there 

 are no structural characters known, either internal or external that 

 may be used to diagnose C hroicocephalus I prefer to include the 

 two species of hooded gulls treated in the present paper in the genus 

 Larus. 



The call notes of the brown-hooded gull suggest those of Larus 

 franklini and are entirely different from the cawing calls of L. cir- 

 rocepJialus that was associated with it in small numbers. In the 

 Province of Buenos Aires maculipennis was common in late June, 

 1920, along the Rio de la Plata. Near Berazategui on June 29 these 

 birds were abundant in flocks that rested on the muddy beaches or 

 flew over the fields inland. Hunters decoyed them within range by 

 waving some white object and killed them in numbers for food. 



From October 22 to November IT the brown-hooded gull was 

 common in eastern Buenos Aires in the vicinity of Lavalle. At this 

 season adults in full plumage Avere found in pairs that stood about 

 in the pampa near little pools of water or that came circling over- 

 head curiously with a scolding Kek Kek Kek to examine any in- 

 truder. At the same time I observed flocks of birds still in winter 

 plumage both on the open plains and along the sea beach below 

 Cape San Antonio. Apparently part at least of the young may 

 require two years to reach sexual maturit}^ and full plumage. 

 Occasional adult birds were observed with these flocks. The species 

 has a slow, flapping flight and with its short square tail, notes, and 

 general appearance is strongly suggestive of Franklin's gull. 



I observed a dozen gulls near General Roca, Rio Negro, on 

 November 30, that may have been the present species. At Ingeniero 

 White, near Bahia Blanca, on December 13, brown-hooded gulls 

 were fairly common over the bay, and near Carhue, Buenos Aires, 

 they were found on the shores of Lake Epiquen. Near Montevideo, 

 Uruguay, in January the species was common. 



Brown-hooded gulls breed in abundance on rocky islets along the 

 coast of the Department of Rocha, eastern Uruguay, and formerly 

 it was the practice to raid these colonies to secure (ggs in large 

 quantities. In recent years the commission charged with oversight 

 of agricultural affairs (the Defensa Agricola) has afforded the gulls 

 absolute protection, a step that has been well merited. Near La 

 Paloma, the seaport town for the city of Rocha, I saw bands of 

 these birds containing as many as 200 individuals feeding in the 

 pastures on the abundant grasshoppers. The gulls were gathered 

 in close flocks that flew slowly, barely above the earth, and as grass- 

 hoppers were discovered dropped to earth to secure them. Those 

 from the rear rose continually to fly over their companions to the 

 head of the column so that the band drifted slowly along, as though 

 blown by the wind, in close though continually shifting formation. 



