COMMON AND ARCTIC-TERNS 77 



The variation shown by individual birds is, however, so great that this 

 means of identification can only be regarded as of secondary or 

 supplementary value. At the Fames, where both species can be seen 

 side by side, I have noted common-terns whose wing-tips fell distinctly 

 short of the tail, and also an individual of each species side by side 

 with the same relative length of wing and tail. The wing-tips of the 

 Arctic may project beyond the tail. In one case quoted they did so 

 by 1| inch (38 mm.). 1 The extent of the variation in either species 

 is well illustrated by Naumann's figures. According to him it has a 

 sexual significance, the females having the shorter tails. 



The common-tern's flight appears somewhat heavier than that of 

 the Arctic ; it seems almost as if, at each stroke, it were lifting 

 weights attached to the tips of its pinions. This is, of course, chiefly 

 noticeable when the bird is flying at a leisurely rate. It is noticeable 

 to a greater or less extent in the case of all its congeners except the 

 little-tern. 



The species can further be distinguished by at least one marked 

 difference in the notes they utter. The ordinary note of the common- 

 tern is a long-drawn strongly dissyllabic keee-yerrrrr ; that of the Arctic 

 a shorter kerrr, occasionally kerr-err. Their remaining notes have yet 

 to be closely compared. According to my observation they are much 

 alike, but I have not heard the two species together, and base my 

 opinion only on the fact that I have used much the same syllabic 

 characters for their notes. From both I have heard a rapid ptip, ptip 

 ptip, ptip. . . . What is the precise significance either of it or the keee- 

 yerrr and kerr I am unable to say. They are possibly both used to 

 express different degrees of alarm. I have heard the kerr and ptip 

 uttered by Arctic-terns when taking their sudden periodic simultaneous 

 flights from the ground after a recent disturbance. I have reason to 

 think that the ptip is also a call-note, and may, in addition, have some 

 sexual significance. There can be no doubt as to the meaning of the 

 third note. This I find I have syllabled for the common-tern as 



1 Vogel Mitteleuropas, xi. p. 138. Or see Journal fur Omithologie, 1899, p. 384 (Schalow). 



