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The best criterion of the species in any plumage, however, is its call note which is very 
different from that of the Common. Instead of a sharp “Tearrrr” it is a woodeny and 
lower pitched “ Churrrr When this difference is once heard and marked it affords the 
most reliable field guide that can be given. 
Nesting. On slight elevations in grassy marshes, in nests built of waste vegetation. 
Distribution. A bird of the prairie interior, probably nesting in any suitab e places 
wherever found in Canada. Not yet reported from British Columbia, although there are 
records from the state of Washington. 
These Terns frequent marshes rather than beaches and do not seem 
to gather in such large flocks on the big lakes as do the Common Tern to 
which they are otherwise very similar in habit. Though common through- 
out the eastern prairie sections they are more local and less generally 
distributed than the Common Tern. 
70. Common Tern. Wilson’s tern. Sterna kirundo. L. 15 (Forking of tail 3*1). 
Plate V A. 
Distinctions. The Common Tern resembles both the Arctic and Forster’s Terns so 
nearly as to require close attention to small details to separate it from them. The certain 
characteristic by which it can be separated 
from Forster’s, but not the Arctic, is the 
coloration of the long outer tail feathers 
which are shaded with dark on the outer 
instead of the inner web (Figure 102). 
The underparts in the adult are also 
delicately shaded with pearly grey, 
averaging appreciably lighter than the 
Arctic but slightly darker than Forster’s. 
This distinction does not always hold with 
juvenile birds. In young or autumn plum- 
ages, the face markings are quite distinct 
from those of Forster’s, but not from the 
Arctic. In the Common Tern, the dark 
face patch suffuses across the nape of the 
neck to meet its fellow from the opposite 
side, making a continuous nape band 
(compare with Figure 101). In juvenility 
the bill is largely flesh-coloured and black, 
and in the autumn adult much of the 
redness is lost. From the Arctic Tem 
distinction is rather more difficult. The grey below does not average quite as deep, but 
this characteristic is not common to all individuals. The forward third of bill of the adult 
Common Tem is black, but the bill of the Arctic is red to the tip. The only distinction from 
that species that holds in all plumages is that of the feet and legs. Those of the Arctic 
Tem are particularly small, the tarsus being not more than 0*65 inch in length; that of the 
Common Tern is not less than 0*8 inch. 
Field Marks. In mixed flocks of Common and Forster’s Terns the Common can some- 
times be distinguished by the Blightly greyish clouding of the white underparts. In autumn 
and juvenility it can be separated from Forster’s by the face mark spreading over the back 
of the head. The best field distinction between the two species, however, is the call note 
which is very different from that of Forster's, which is a sharp “Teanr” instead of a duller 
and more woodony-sounding “ Chum .” From the Arctic Tem differentiation is more 
difficult. The black-tipped instead of all red bill may be made out under favourable 
circumstances. When on the ground the Common Tem stands up higher on its legs than 
the Arctic Tern. The latter hugs the ground with its body as it walks, and has a mouse- 
like glide. The Common Tem is likely to be confused with Forster’s only in the 
interior, and with the Arctic only on the Pacific coast. 
Nesting. On sandy or gravelly bars. Eggs laid directly on the ground. 
Distribution. Across the continent, breeding north to the Arctic. This is the most 
abundant Tem in the prairie interior and in British Columbia. 
Common, especially in the interior about sandy shores, scarcer on 
rocky ones. The Common Tern may be seen on most of our larger bodies of 
water, salt or fresh, throughout the summer. Its wonderful lightness of 
Figure 102 
Specific details of Common Tem; tail and 
head of juvenile or winter plumage; 
scale, J. 
