COMMON TERN. 233 



back of neck of the adult bird are bluish grey in winter. 

 Length, 16 ins. Wing, 12 ins. Tarsus, i'4 ins. 



Common Tern. Sterjia himndo Linn. 



The Common Tern (Plate 103) has a wide Palosarctic and 

 Nearctic range, and in winter migrates far south. In the 

 British Isles it is certainly the commonest tern in most parts ; 

 it nests all round our shores, least plentifully in the north, and 

 large numbers visit us on passage. 



"Sea-Swallow" is a name given to all the commoner terns, 

 but except in the long, pointed wings and forked tail with 

 streamers, there is little to suggest a Swallow. The Common 

 and Arctic Tern can with difficulty be distinguished on the 

 wing, though in the hand the characters are clear. Broadly 

 speaking, the bill of the Common is red with the distal third 

 dusky or almost black, and that of the Arctic coral-red through- 

 out or with only the extreme tip dark. The safest guide is the 

 white-shafted outer primary, dark slate in both on the outer 

 web, but with a paler slate stripe on the otherwise white inner 

 web. In the Common this stripe is twice as wide as the outer 

 vreb ; in the Arctic the two are about the same width. The 

 Common Tern has a slightly longer tarsus, and therefore stands 

 a little higher, but this is difficult to judge in life, as is the paler 

 greyish suffusion of the under parts. On the average the 

 wings of the Common are longer and its tail streamers shorter 

 than those of the Arctic, but the position of the tips when the 

 wing is closed varies according to the pose of the bird and is 

 an unsafe guide. The difference in the voice can only be 

 learnt by experience. The Common Tern is one of our best- 

 known sea-birds. It beats over the waves with slow and 

 deliberate but powerful strokes; the determined down-strokes 

 look as if they should jerk the slender, cigar-shaped body 

 upward. It poises in the air with upraised wings vibrating. 



