AVES LARID^E. 1 89 



Bill : Stout and deep at base and entirely greenish yellow, without black 

 tip. Tarsi : Dull yellow. Feet : Dull yellow. Iris : Dark hazel brown. 



Adiilt. Autumnal and winter plumage. Similar to the breeding 

 dress but with the black loral streak broken into black dotting or specks ; 

 the black of the cap much flecked and spotted with white feathers. 



Immature birds of the year in fall. Like adults, except the lores are 

 wholly white ; forehead white ; crown grey with dusky streaks ; around 

 the eye these being concentrated form a broad dusky band on each side 

 of the head, which reaching back joins on the nape ; the primaries have a 

 browner shade ; the bill is dull yellow with a brownish horn tip. 



Young. Flight age. Lores greyish; a marked whitish superciliary 

 stripe ; crown darker than lores, specked with dark brown ; a blackish 

 band extending from eye to eye, across the nape ; mantle grey, shaded 

 with buffy and barred with ashy grey ; tail mottled with ashy on a grey 

 ground ; base of bill dull yellow shading into horn color ; tarsi and toes 

 dull yellowish. 



Geographical Range. South America. From the Orinoco to the La 

 Plata, ascending rivers well into the interior ; Northern Patagonia. 



This small tern was not obtained by the Princeton Expeditions to Pata- 

 gonia, where it is apparently uncommon if not rare. The diagnoses and 

 descriptions of different plumages are based on material in the British 

 Museum of Natural History. Closely allied to S. antillarwn, the changes 

 in plumage due to age, and correlated with the seasons are very similar 

 in both species, but the difference in size and the color of the primaries 

 serve at all times in readily distinguishing the two species whose geo- 

 graphical ranges almost or quite meet. 



"Of these, three or four were observed wheeling about over the river 

 Saima, about a league up it from the Parana. They have a sprawling, 

 quick flight, settling now and again on the rocks on the edge of the river. 

 Dashing down and skimming the water, they dip every now and again 

 for fish, after which they rise high in the air." (E. W. White, P. Z. S. 

 p. 628, 1882.) 



