SILVER-WINGED BLACK TERN. 
107 
when they are closed. The beak, which is shorter and 
stouter at the base than in the Sterna nigra, measures one inch 
from the forehead to the tip. The legs and feet are larger 
than those of the foregoing species ; the naked part of the 
tibia is five lines long ; the tarsi ten lines ; the middle toe, 
including the claw, one inch, and the hinder toe, including the 
claw, four lines. 
The summer plumage of the adult bird is very handsome: 
the head, neck, back, breast, and belly, nearly as far as the 
abdomen, are pure black, as also the under wing-coverts ; the 
plumage of the head and neck reflect a green silky gloss. The 
edge of the wing is white ; the lesser wing-coverts are nearly 
white, which colour deepens into pearl grey further down the 
wing, and the grey becomes more and more decided until it 
loses itself in the deep slate colour of the tertials ; the quill- 
feathers are cinereous ash colour, darkest at the tips and outer 
web of the first quill, which is the longest feather in the wing ; 
the rump, vent, upper and under tail-coverts and tail are pure 
white. The male and female are alike. Beak dusky black, 
red at the base and gape ; the legs and feet coral red ; the 
iris brown. 
The moult in summer begins in July and the beginning of 
August, wherefore a few may be seen in their chequered garb 
before they leave their breeding localities. 
The plumage of the summer moult is as follows :—The 
chin is white ; the head and all the under plumage white, 
with black tips to the feathers on the top of the head, nape, 
cheeks, and ear-coverts, producing a very chequered appear¬ 
ance ; the space between the beak and eye, and the region of 
the eye, white ; the breast and belly appear barred with blaek 
and white, owing to the broad black edges of the feathers ; 
the upper part of the back is black ; the wings, tail, vent, and 
tail-coverts as in summer, but the grey on the wings and ter- 
