NATURAL HISTORY OF SOUTH AFRICA 



is being formed. Sometimes the variation in colour 

 is due to an access of carbonate of lime being deposited 

 on the shell, as instanced in many sea birds' eggs. 



The colouring and markings on birds' eggs are 

 certainly, in the great majority of instances, for the 

 purpose of rendering them less conspicuous to enemies. 

 The reptilian ancestors of birds laid white eggs, as 

 they do to-day, and buried or otherwise hid them. 

 Many species of birds which lay white eggs cover 

 them up when they leave the nest. The doves and 

 pigeons have white eggs which are very conspicuous 

 lying in their flimsy bed of twigs, but both sexes of 

 these birds assist in the incubation process, and 

 consequently the eggs are seldom exposed. 



The colour and markings, for instance, of plovers' 

 and lapwings' eggs render them so inconspicuous that 

 it is extremely difficult to see them even when close 

 at hand and within full view. The eggs of birds 

 which nest in holes are usually white. There are 

 many exceptions, however. Some of the South African 

 species of starlings which nest at the ends of deep 

 holes in banks produce blue eggs. Again, many of 

 the weavers, bishop, and widow birds build domed 

 nests, and the eggs are not visible to enemies, yet 

 the majority of them have coloured and spotted eggs. 

 The causes of the coloration of birds' eggs need a 

 great deal more study before we can dogmatise on the 

 subject. 



Eggs vary a good deal in shape. Those of 

 many birds which deposit their eggs on rocks and 

 ledges of cliffs are shaped in such a way that they 



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