BRITISH BIRDS' NESTS. 361 



it is gratifying to be able to say they have, during 

 the last decade or two, increased in numbers on 

 Hernia Ness in Unst, at any rate. 



Materials. All the nests I examined in the 

 Shetlands some years ago were made of dead grass 

 and bents in varying quantities. In nearly every 

 case a mock nest had been built not far from the 

 one containing eggs, and the birds have been known, 

 when an original nest became flooded through 

 heavy rains, to convey their eggs to the supple- 

 mentary structure. 



Eggs. Two, occasionally only one, varying from 

 light buff to dark olive-brown, blotched and spotted 

 with dark brown and rusty- or greyish-brown. 

 Similar to Lesser Black-backed and Herring Gulls, 

 but markings are fewer and duller, and presence 

 of parent birds readily settles the point. Size 

 about 2.85 by 1.95 in. (See Plate XI.) 



Time. May and June. 



Remarks. Migratory, arriving at its breeding 

 haunts in April and leaving in August. Notes : 

 ag-ag and skua. Local and other names : Great 

 Skua, Bonxie, Brown Gull, Skua Gull, Morrel Hen. 

 Gregarious. Sits lightly and readily attacks a 

 single human intruder approaching its nest and 

 eggs or young. The method of attack is to swoop 

 from a considerable height at a terrific speed, and, 

 when sufficiently close to the intruder, to drop both 

 feet and hit him with their fronts on the back of 

 the head. As soon as the blow has been delivered 

 the birds shoot upwards, and circle round for a 

 fresh attack. According to my experience they 

 never strike the object of their resentment in 

 the face. 



