The Zoologist — November, 1867. 975 



always has the base of the bill yellow and the extremity black. In 

 the domestic bird it is just the reverse. 



Common and Arctic Terns. — The habits of both Sterna Hiiundo and 

 S. arctica are very similar, and their general resemblance such that, 

 except by the note (which is difficult to imitate), it is impossible to 

 distinguish them on the wing at any distance. When endeavouring 

 to point the distinctive characters of these two species, many authors 

 give measurements of the wing, tail and total length ; but, from an 

 examination of a great number of specimens of each, it appears that 

 individuals of the same species vary so much, according to sex and 

 age, that these measurements are practically of but little use. We are 

 also told that the arctic tern is always much darker beneath than its 

 congener : generally speaking this is so, but we have seen some 

 common terns, shot in June, when in full summer plumage, which were 

 quite as dark as many arctic terns which we have examined. Again, 

 many naturalists say that while the bill of the common tern is red, 

 with a black tip, that of the arctic tern is invariably red throughout its 

 whole length ; but this is only the case with fully adult birds. The 

 young of both species at first have the bill of a dark horn-colour, 

 orange-red at the base. As the bird gets older the daiker colour 

 recedes further from the base, while the red becomes brighter, and 

 finally only the tip of the bill remains black in the common tern, while 

 in the arctic species the black colour disappears entirely. The only 

 features which really appear to be constant, and may consequently be 

 considered indicative of the species, are the comparative length of bill 

 and tarsus, and the length of the closed wings in proportion to the tail. 

 In a few words, the differences may be shortly stated as follows : — 



Common Tern. 



Bill longer and stouter, average = 

 2 inches; red, black at tip. 



Tarsus longer, average 8£ lines. 



Tail equal to, or (generally) shorter than 



closed wings. 

 Under parts whiter. 

 Black cap, extends perhaps a little further 



and is more pointed in form. 



Aectic Tern. 



Bill shorter and more slender, average 

 = 1 inch 6 lines; in old bird red 

 throughout. 



Tarsus shorter, average 6£ lines. 



Tail longer than closed wings. 



Under parts grayer. 



Black cap rather shorter and more 

 rounded in form. 



This last statement requires confirmation. 



J. Edmund Harting. 

 Kingsbury, Middlesex, September, 1867. 



