OP THE BEITISH ISLANDS. 11 



either in clefts and fissures of the cliffs or in caves, those being preferred which 

 are always inaccessible to man save by the use of a boat. In the latter situations 

 the nest is placed in the clefts and crannies of the rugged roof, or on ledges and 

 prominences of the walls. Numbers of birds breed in company, the size of the 

 colony depending to a great extent on the suitability and resources of the site 

 chosen. The nest is slight enough a few bits of grass or seaweed, a few roots or 

 twigs, or dry stems of weeds ; whilst even green grass has been known to be used. 

 The eggs are two in number, oval in form, and pure white in colour. They 

 measure on an average 1'4 inch in length, and 1'2 inch in breadth. These birds 

 pair for life, use the same nesting-places year after year, and both parents assist 

 in the duties of incubation which lasts from sixteen to eighteen days and in the 

 care of the young. These are brought to maturity in a similar manner to their 

 congeners, and are deserted as soon as they leave the nest. 



Diagnostic characters. Columba, with two well-defined black wing 

 bars, a pure white rump, and white axillaries and under wing coverts. Length, 

 11 to 12 inches. 



