288 BRITISH BIRDS. 



on the sides of the head, nor to the gape on the lores. The general colour 

 of the rest of the upper parts is French grey, darker on the quills, and 

 paler on the rump and upper tail-coverts ; the outer web of the outer tail- 

 feather on each side and the outer web of the primary are generally a 

 darker grey ; the inner webs of the primaries are broadly margined with 

 white, frequently almost reaching to the shaft, but seldom to the tip of 

 the feather, and always forming a well-defined pattern. The wings and 

 tail are generally very long, and the latter more or less deeply forked. 

 The whole of the underparts, including the under wing-coverts, are 

 generally pure white. The colours of the bill, legs, and feet vary in each 

 species. After the autumn moult, which generally takes place during 

 August, the black disappears from the forehead, and that on the crown 

 and nape is streaked with white. After the first spring moult, which 

 generally takes place during February, the amount of black on the head 

 is intermediate between that of adult summer and adult winter plumage, 

 and the lesser wing-coverts are more or less streaked with brown. Birds 

 of the year (a plumage which follows so closely upon that of young in 

 first plumage that the moult to the former may be said to begin as soon 

 as the latter is completed) have pale margins, emphasized by brown sub- 

 margins to the scapulars, innermost secondaries, and the tips of the tail- 

 feathers. In young in first plumage these pale margins are buff, and the 

 sub-margins dark brown, and they extend to the feathers of the mantle 

 and to the ear-coverts, and traces of them are to be found on the upper 

 tail-coverts and on the feathers of the rump and breast. 



The Arctic Tern is slightly less than the Common Tern, though it 

 measures the same in length of wing, and the fork of the tail is about the 

 same. In the general colour of its plumage and the variations which it 

 undergoes it is typical, except that the rump and upper tail-coverts are 

 pure white and the underparts are suffused with French grey. In adults 

 the bill, legs, and feet are deep crimson ; but in young birds these parts are 

 duller in colour; irides hazel. The adult Arctic Tern may be distinguished 

 from the Common Tern by the slightly darker French grey of the under- 

 parts, and at all ages and seasons by its shorter tarsus (which scarcely 

 exceeds half an inch in length, instead of nearly approaching three quarters 

 of an inch) and by the greater amount of white on the inner web of the 

 first two or three primaries. In the Arctic Tern the grey stripe along the 

 shaft on the inner web is no broader than the outer web, whereas in the 

 Common Tern it is nearly twice as broad. 



Young in down have the upper parts greyish brown mottled with black, 

 and the underparts pure white clouded with brown on the flanks and vent ; 

 but the throat, sides of the head, and forehead are dull black. 



