292 THE NESTS AND EGGS OF BRITISH BIRDS. 



particular spot. The nest is generally made on a stack 

 of rocks, or a ledge of the cliffs ; less frequently on tb.e 

 ground, on an island. It is slight and loosely put 

 together, a mere hollow in most cases, carelessly lined 

 with grass, twigs, dry sea-weed, or stalks of marine 

 vegetation. I have known the eggs to be laid on the 

 bare ground, in a hollow amongst the crags. The birds 

 sit lightly, but are bold and clamorous when disturbed 

 from the nest. 



Range of egg colouration and measurement : 

 The eggs of the Great Black-backed Gull are usually 

 three in number, less frequently two, and rarely even one. 

 They vary from grayish-brown to brown tinged with 

 olive in ground colour, spotted with dark umber-brown, 

 and with underlying markings of brownish-gray. As a 

 rule the markings are not very numerous, range in size 

 from that of a buckshot downwards to a speck, and are 

 distributed over most of the surface. Some varieties, 

 however, are most heavily marked on the larger end. 

 Average measurement, 3"i inches in length, by 2"i inches 

 •in breadth. Incubation, performed by both sexes, lasts 

 about a month. 



Diagnostic characters: The large size and small 

 markings readily distinguish the eggs of this Gull from 

 those of allied species breeding in our islands. 



