22 THE AUKS 



have been seen to bring what might serve for nest material (feathers, 

 grass, roots) to their mates, and lay it on the rock before them, where 

 it is sometimes pulled about by both. 1 This may be mere play, but it 

 has at least some appearance of being the survival of a lapsed nest- 

 building instinct, granted that the primitive plover from which the 

 Auks are descended had acquired the instinct, which, after all, is an 

 assumption. If it had the instinct, there at once arises a difficulty in 

 explaining why it should have lapsed. That there is nothing in the 

 nature of the nesting sites occupied by guillemots and razorbills to 

 prohibit the construction of a nest is a fact to which the kittiwake, 

 gannet, and puffin bear witness, particularly the two first named, which 

 erect particularly solid structures on ledges often exactly similar to 

 those which a guillemot might choose. The kittiwake, let us note, 

 like other gulls, is also descended from plover stock. Possibly the 

 Gulls branched off from stock in which the nest-building instinct had 

 become well established, and the Auks did not. The nest-building 

 instinct of the puffin may have been subsequently acquired. 



The fact that razorbills and guillemots lay one egg can be explained 

 by the large size of the egg and by the difficulty of incubating more 

 than one on bare rock-ledges, where the eggs would tend to roll 

 apart in the absence of cup-shaped depressions such as are provided 

 by a nest or a scrape in the soil. Yet the gannet also lays one 

 egg in a nest ! 



The extraordinary variation in the coloration of guillemots' eggs 

 has often been remarked, and provides one of the excuses for collect- 

 ing them in large numbers, though the collectors remain, for the most 

 part, singularly reticent about the scientific results of their labours. 

 The variation extends not only to the colour and shape of the markings 

 but also to the ground-colour, which may be white, blue, green, brown, 

 yellow, buff, or pink. (PI. G.) The variation in the razorbills' eggs are 

 less marked, not more so than in those of many other species. 



The variation, in the case of guillemots' eggs, has been explained 



1 E. Selous, Bird Watching, pp. 194-5 ; Bird Watcher in the Shetlands, p. 109. 



