286 THE NESTS AND EGGS OF BRITISH BIRDS. 



until spring. It is social during the breeding season, 

 nesting in scattered colonies, the pairs being distributed 

 over a considerable area of moor. The nest is invariably 

 on the ground, and in most cases is little more than a 

 hollow in the moss, sometimes lined with a few bits of 

 dry grass. The Great Skua is not a close sitter, rising 

 from its eggs as soon as its haunts are invaded, and 

 swooping boldly round the head of the intruder, courage- 

 ously endeavouring to drive him from the sacred spot. 



RANGE OF EGG COLOURATION AND MEASUREMENT : 

 The eggs of the Great Skua are two in number. They 

 vary from pale buff to dark huffish-brown or olive-brown 

 in ground colour, somewhat obscurely spotted and 

 speckled with dark brown, and with underlying markings 

 of grayish-brown. As a rule the spots are most 

 numerous, and many of them often confluent, on the 

 larger end of the egg. Average measurement, 2*9 inches 

 in length, by 2*0 inches in breadth. Incubation, per- 

 formed chiefly by the female, lasts about a month. 



DIAGNOSTIC CHARACTERS : As this species is so very 

 local during the nesting season, its eggs cannot readily 

 be confused with those of any other species breeding 

 within our area. Away from the nest, however, they 

 cannot always with absolute certainty be distinguished 

 from those of the Herring Gull and the Lesser Black- 

 backed Gull. A seldom-failing point of distinction, 

 however, is the much more obscure and ill-defined spots 

 on those of the Great Skua. 



