486 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 



oae species (S. melanogastra) with under parts of body mostly black. 

 Downy young buffy or brownish above, irregularly spotted or marbled 

 with blackish; in one species (S.fuscata) streaked above with dusky 

 and buffy grayish, in varying relative proportion. ° 

 Range. — Cosmopolitan. (Sixteen, or more, species.) 



KEY TO THE SPECIES OF STERNA. 



(Based on adults only.) 



a. Back, scapulars and wings clear gray, not darker (usually paler) than neutral gray, 

 the tail white or mostly white; inner webs of primaries largely white. 

 b. Pileum and nape immaculate white; under parts pale gray like upper parts; 

 bill yellow with a sub terminal band of black. (Coasts of southern South America, 

 from Brazil to Chile; casual on Long Island and coast of New Jersey.) 



Sterna trudeaui (p. 488). 

 bb. Pileum, at least partly, the nape wholly black; under parts white or if gray the 

 color decidedly paler than that of upper parts; bill not yellow nor with a 

 black sub terminal band, 

 c. Pileum entirely black in summer. 

 d. Inner web of lateral rectrix gray or dusky terminally, the outer web entiiely 

 white; bill orange; tarsus 21.5-24 mm., middle toe 19.5-22.5 mm. (Temperate 

 North America, in winter southward to Guatemala.).. Sterna forsteri (p. 490). 

 dd. Inner web of lateral rectrix white throughout, the outer web gray or white; 

 bill red or black; tarsus not more (usually much less) than 20 mm., middle 

 toe not more (usually much less) than 19 mm. 

 e. Outer web of outermost rectrix dark gray; under parts of bod,y not pure 

 white (more or less grayish); bill mostly red at all seasons; wing usually 

 more than 235 mm. 

 /. Tarsus, 17.5-20 mm., longer than middle toe without claw; tail forked 

 for usually less than 102 mm.; under parts of body paler gray (pallid 

 neutral gray to grayish white) ; bill and feet vermilion or orange-red 

 (Northern Hemisphere; south in winter as far as southern Afiica 



India, and Brazil.) Sterna hirundo (p. 493). 



ff. Tarsus 13.5-17 mm., shorter than middle toe without claw; tail forked 

 for usually more than 102 mm.; under parts of body deeper gray (pale 

 neutral gray) ; bill and feetcarmine red. (Northern portions of Northern 

 Hemisphere in summer; said to winter in Antarctic Ocean.) 



Sterna paradisaea (p. 499). 

 ee. Outer (as well as inner) web of outermost rectrix white; under parts of 

 body pure white (often suffused with pink) ; bill mostly black in summer, 

 red basally in winter; wing usually less than 235 mm. (Nearly cos- 

 mopolitan in temperate and tropical regions, mostly along sea- 

 coasts.) Sterna dougalli (p. 505). 



cc. Forehead and sides of crown white; a black stripe from bill to eye. (Coasts of 

 Bering Sea and southward to Kadiak Island and Japan.) 



Sterna aleutica (p. 510). 



alt may be that S.fmcata should be separated generically (as Onychoprionfuscata), 

 on account of the conspicuously different young, both in down and in first plumage, 

 and possibly some details of structure which, however, I have not been able to dis- 

 cover. But in this case S. anxthela and S. lunata, which have usually been asso- 

 ciated with S.fuscata must remain in Sterna, for they do not agree with S.fuscata in 

 coloration of the young . 



