166 BRITISH BIRDS, THEIR EGGS AND NESTS. 
named, but usually distinguishable by the larger masses of 
surface colouring, and by some superiority in size. The Black 
_back’s eggs are much esteemed as articles of food, or for cooking 
purposes generally. The yolk is very deep and rich-coloured, 
and the white colourless or transparent. ach female will lay 
three sets of eggs; the first two sets being, in some cases, 
customarily taken, and the last left for her to hatch. 
312. GLAUCOUS GULL—(Larus glaucus). 
Large White-winged Gull, Burgomaster.—A Gull equally large 
with the last, one of which, shot by myself, exceeded six feet 
from the tip of one wing to that of the other; but one of merely 
casual occurrence as a British bird. 
3138. COMMON SKUA—(Leséris catarractes). 
Skua Gull, Brown Gull, Bonxie-—We pass here into a some- 
what different class of birds. The Skua is as bold and insolent 
as most of the Gulls are timid and retirmg. In many instances 
these birds do not take the trouble to fish for themselves, but, 
watching the fishing operations of the Gull, seize their oppor- 
tunity of assailing a successful fisher, and compel him to disgorge 
his prey. The Common Skua has only a very limited breeding- 
range in Britain, not being known to nest out of Shetland, and 
to have but three places for nidification there. So resolute and 
daring are they when they have young to defend, they do not 
scruple to attack the eagle, and a pair have been known to beat 
the strong, proud marauder effectually off. The Skua makes a 
large nest of moor-growing moss, and takes some pains in its 
construction. It is placed among the heath and moss of a hilly 
island. The eggs are two in number, and vary much in colour; 
according to locality it would almost seem. Some are dusky 
