THE AUKS 271 



the end of February, and the paired birds do not settle finally upon 

 the rocks until the beginning of April, or even, in the far north, a 

 month later. Razorbills, too, migrate farther south than guillemots, 

 which may be seen throughout the winter in home waters. 



Puffins winter in deeper water farther at sea and are later in return- 

 ing to the breeding ground, being seldom seen within sight of land, 

 except casually, until the early part of March. At large colonies on 

 the southern coasts of England, Wales and Ireland puffins settle on 

 the water under their breeding cliffs with great regularity during the 

 last week of March (in the north of Scotland and the Faeroes in mid- 

 April) . Yet although they are the last of the three common auks of 

 Britain to arrive at their breeding grounds, puffins are the first of the 

 auks to lay, and eggs may be found in the last fortnight of April, 

 long before the main colony has settled permanently on land. This 

 is some four weeks before egg-laying in the guillemot and the razorbill ; 

 and as we shall see in describing its breeding biology this early laying 

 is probably connected with the much longer incubation and fledging 

 periods of the puffin. Little auks return to the arctic land before it is 

 free of winter and perform their courtship on ice in May and early 

 June. 



The three species of guillemots (the common, Briinnich's and 

 the black) have been placed by many systematists in one genus; but 

 the black guillemot, by its choice of habitat, more closely resembles the 

 razorbill and the little auk; and it differs much from the other guille- 

 mots and the razorbills in having two eggs, a more markedly different 

 winter plumage, and a different pelvic design. It lays its eggs (normally 

 two) in a crevice under stones or boulders; in this well-protected site 

 the young are comparatively safe, and do not leave the nest until they 

 are fully grown and able to look after themselves. In this they resemble, 

 not the razorbill, but the puffin. The majority of razorbills lay their 

 eggs in more exposed situations where they are more subject to the 

 depredations of gulls; only a minority nesting under stones or out 

 of sight in holes. 



We thus have an interesting ecological division of the rocky cliffs: 

 the common and Briinnich's guillemots occupying the most exposed 

 platforms and shelves, and the cliff-top, and rarely laying the egg under 

 the protection of the talus; the razorbill, sometimes laying its egg 

 upon ledges exposed to sun and wind, but usually nesting in more 

 sheltered situations in the shadows of fissures and under boulders, and 

 even well inside rabbit or puffin holes in the cliff; the black guillemot 



