62 
head first with a splash of white spray in which for a moment they dis- 
appear, but they never go far under water. 
64. Caspian Tern (Including American Caspian Tern). Sterna caspia. L, 21 
(Forking of tail 1 -50 1 ). The largest of our Canadian Terns. In colour very similar to the 
Common Tern (See page 63 and Plate V A). 
Distinctions. Large size of this Tern is characteristic. The Caspian Tern is as large 
as some of the smaller Gulls; but its bill, though comparatively heavy for a Tern, is too 
graceful and tapering to be gull-like. 
Field Marks. Rather distinctively marked in life. In size, it is more likely to be 
compared with a Ring-billed Gull than a Tern, but its big red bill, black cap, slightly 
forked tail, and general tern-like coloration are plain. The slow'beat of its long wings is 
different from the more quickly moving small Tern and its voice is raucous; a single 
hoarse monosyllable that may be rendered “Casp” is characteristic. 
Nesting. On sandy beaches, or rocky or gravelly islands. 
Distribution. A nearly cosmopolitan species. Found in the Old as well as the New 
World. Occurs rather irregularly all over Canada, but its known nesting stations are few 
and scattered over the continent from Great Slave lake to Labrador. 
SUBSPECIES. The American Caspian Tern has been lately separated from that of 
the Old World under the name of Sterna caspia imperator. 
We have breeding records for this species on lake Winnipeg and Great 
Slave lake and occasional sight records down through the Prairie Provinces 
and southern British Columbia. 
Economic Status. Though probably a fish feeder and the largest of its 
subfamily the Caspian Tern is too scarce and its food is too small to have 
any appreciable economic influence. 
A particularly beautiful and interesting bird. Its wide range, scat- 
tered breeding stations, and growing scarcity suggest that the numbers 
we see today are the remnants of a once much more numerous and generally 
distributed race and that if we are to have it with us in the future special 
care should be taken to guard its local nesting communities from molestation. 
The most 
69. Forster's Tern. Sterna for steri. L, 15 (Forking of tail 4-1). Plate IV B. 
Distinctions. Forster’s Tern so nearly resembles both the Common and the Arctic 
Tern as to require close attention to small details to differentiate it from them, 
determinative characteristic by which 
it may be separated from any other 
species is the coloration of the long 
outer tail feathers, which are shaded 
with dark on the inner instead of the 
outer web (Figure 101). The underparts 
are also pure white instead of Being 
delicately shaded wth pearly grey. In 
juvenility and autumn or winter plum- 
ages, the face markings are quite 
characteristic. In Forster’s Tern the 
dark face patch is sharply defined and 
does not overspread the nape to meet 
its fellow from the other side (compare 
with Figure 102). In juvenile and 
winter plumages the bill is largely or 
completely black. 
Field Marks. In mixed flocks of 
Common and Forster’s Terns the latter 
can sometimes be distinguished by the 
superior silvery-whiteness of the under- 
parts. The juvenile and autumn plumages are separable by the face mark being confined 
to the cheeks and not spreading across the back of the neck to make a dark nape band. 
Figure 101 
Specific details of Forster's Tern; tail and head 
of juvenile or winter plumage; 
scale, j. 
1 This measurement shows the difference in length between the middle and outer tail feathers. A groat 
part of the total length of these birds is in the greatly elongated outer tail feathere and these do not reach their 
maximum in juvenile birds. Hence this figure is given to correct the often times greatly misleading nature of the 
■sual length measurement. 
