1903 Notes on the Nests and Eggs of Birds 137 



The shape of birds' eggs varies considerably from globular 

 or spherical to different modifications of the elliptical or 

 oval — the extreme pyriform of the Waders being the 

 greatest departure from the reptilian shape. The bright 

 and varied colour of many birds' plumage is utilitarian, as is 

 also the beauty of some of their nests and eggs ; but there 

 is no question of love of display involved in the colouration 

 of eggs or the construction of nests, and so also the laws 

 which govern the shapes of eggs are those of expediency. 

 As we have seen, where the eggs are large in proportion to 

 the size of the bird which is to incubate them, the eggs 

 must be of such a shape as to fill the least possible space ; 

 and when no nest is made to receive them, they must, for 

 their best advantage, be so shaped as to be least liable to be 

 tumbled or blown away from the place wherein or whereon 

 they are deposited. This accounts for the pyriform shape 

 taken on by the eggs of Waders and some cliff-breeding 

 birds. The spherical shape persists only with such birds as 

 lay in places where there is no danger of dislodgment. 

 The kingfisher, for instance, makes its rude nest at the end 

 of a tunnel in the ground, whilst the tawny owl chooses a 

 hollow tree for its lying-in chamber. The perfect ellipse is 

 represented by the eggs of the nightjar, and very nearly by 

 those of the sand-grouse and swift. Those in which the 

 ellipse is most perfect lay two eggs only, and brood over one 

 on either side of their sternum. The biconical specialisation 

 occurs amongst the grebes, the greater weight being in the 

 middle of the egg, and the ends thereof being equally balanced 

 tends to the horizontal position being maintained by them in 

 the easily compressible nest. 



( To be continued in our next. ) 



