BIRDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 139 



while the elongate tips of the outer tail feathers had been entirely 

 lost. 



At Guamini, Buenos Aires, on March 7, 1921, I saw a flock of 

 10 slender, black-capped terns that seemed to be the present species, 

 but I did not approach near enough to them to secure specimens. 



STERNA SUPERCILIARIS Vieillot 



Sterna supcrciliaris Vieillot, Nouv. Diet. Hist. Nat., vol. 32, 1819, p. 176. 

 (Paraguay.) 



This handsome little tern Avas seen first at Puerto Pinasco, Para- 

 guay, on September 3, 1920, when one was observed feeding along 

 an estero near the Paraguay River. On September 30 in the same 

 vicinity I encountered two that rested on dead stubs in the water or 

 circled about in the air. A carancho {Polyhoms p. hrasiliensis) 

 passed overhead and one of the terns pursued it for some time with 

 sharp metallic cries. A male in full adult plumage was tolled 

 within range by waving a hankerchief. On January 9, 1921, on 

 the beach near Carrasco, east of Montevideo, Uruguay, I encountered 

 two pairs of these small terns, evidently on their nesting grounds as 

 they darted constantly at my head with complaining cries until I 

 had passed beyond their bounds. On January 31 near San Vicente, 

 in the Department of Rocha, I found a dozen, all immature, beating 

 back and forth over the Laguna Castillos in company with Trudeau's 

 terns. Though young these birds were expert as fishermen, and were 

 so wary that I had difficulty in shooting one. The bill in this speci- 

 men, a female, is not yet fully formed as it is only three-fourths as 

 long as that of adults. The bird is still in mottled juvenal plumage. 



In habits and form this species is suggestive of the least tern and 

 frequents similar localities along large fresh-water streams or sea 

 beaches. 



The adult male secured had the soft parts colored as follows: Bill 

 wax yellow ; tarsus and toes, olive ocher ; crus, yelloAvish olive ; claws, 

 black ; iris. Rood's brown. Measurements of this specimen are : 

 Wing, 189; tail, 82; exposed culmen, 36.6; tarsus, 16.8 mm. 



In a small series birds from Colombia and British Guiana seem 

 a trifle smaller than those from Paraguay. 



THALASSEUS MAXIMUS MAXIMUS (Boddaert) 



Sterna maxima Boddaert, Tabl. Plaucb. Enl. d'Hist. Nat., 1783, p. 58. 

 (Cayenne.) 



On November 4, 1920, I shot a male royal tern on the beach 24 

 kilometers below Cape San Antonio, on the coast of the Province of 

 Buenos Aires. The bird was found in company with smaller terns. 

 November 15 several were noted in the mouth of Rio Ajo and in 



