320 LONG-WINGED SWIMMERS — LONGIPENNES. 



abrupt and marked contrast with the sooty black of the lores and orbital region. Only the upper 

 half of the head is blackish, this color forming a well-defined "hood," as in the species of Sterna, 

 its lower edge on a line with the rictus, and including the auriculars ; the lower eyelid being marked 

 by a whitish crescent. Only one example in the very large series of American specimens approaches 

 tin- darkest-colored individual from Europe, and even in this instance the difference is very decided. 

 In his paper on the Stemina (P. Z. S. 1876, p. 643), published subsequently to Dr. Coues's mono- 



Winter plumage. 



graph in " Birds of the Northwest," Mr. Howard Saunders remarks as follows concerning the 

 differences between the American and the European birds of this species : — 



" In almost all the adult American specimens which I have examined — about a dozen in num- 

 ber — the black of the under parts is of a deeper and more sooty blown tint than in any European 

 examples out of upwards of a hundred from various localities, the black being as dark as in 

 //. leucoptera — an intensity of line which our form never possesses. In two or three examples, 

 however, all females, the lightest colored American birds approach more closely to very dark 

 specimens from Europe ; and in the young and winter plumage the two forms are absolutely undis- 

 tinguishable ; so that any specific separation is out of the question." 



The geographical difference in coloration as exhibited in the series before us, which in pro- 

 portionate numbers of the two forms is just the reverse of that examined by Mr. Saunders, is so 

 very marked that it is only in view of the possible intergradation through the lighter American 

 anil the darker European examples that we consider them as specifically identical. The extreme 

 and average measurements of live adults of the European form are as follows : Wing, 8.40-8.75 

 inches (average, 8.56); tail, 3.50-3.7O (3.60); culmeii, 1.05-1.10 (1.09); depth of bill through base, 

 .20-.2o (.22); tarsus, .60-68 (.62); middle toe, .55-.(i5 (.58). 



The Black Tern is a cosmopolitan species, common to both continents. It is dis- 

 tributed, at different seasons, in nearly all parts of North America; regularly and 

 abundantly in some regions, occasionally and in small numbers in others. It is found 

 throughout Central America and Mexico, and in South America as far south at least 

 as Chili, and north to the Fur Regions and Hudson's Bay. Examples of this bird 

 were taken near Fort Resolution, Fort Yukon, and Moose Fort, and it is abundant in 

 the Red River and Selkirk settlements. 



In Great Britain this bird is only a summer visitor, differing from all the other 

 Terns in some of its habits, seldom associating with any other species, and being 

 rarely seen on the sea-coast, and then only in the spring, at the time of its arrival, 

 or in the fall, when about to leave for the winter. Preferring fresh-water marshes, 

 tlif vicinity of rivers, and reedy pools, it is found in the summer only in the interior. 

 It is rare in the north of England, and makes its appearance in the southern part by 

 the end of April or the beginning of May, and leaves early in October, being very 

 rarely seen as late as November. 



This is said to be a common bird in Sweden; it is also abundant in Holland and 

 in Germany, as well as in the extensive marshes of Hungary. It visits several 



