THE EGGS 



nest is robbed at the time the hen bird is laying, or 

 before she begins to sit, in many instances she will 

 lay a second clutch, and often several batches if the 

 eggs are removed from the nest when laid. I have 

 never yet observed any species of bird produce a second 

 clutch of eggs after being robbed of her first clutch 

 on which she had been sitting. When all the eggs 

 are removed, very few species of birds will lay a second 

 clutch in the same nest. A clutch of eggs is a full 

 set, and they range from one to about twenty, according 

 to the species of bird. The birds (praecocial) whose 

 young are active and do not remain in the nest after 

 birth, usually, but by no means always, produce far 

 more eggs than those (altricial) whose young are help- 

 less and remain in the nest for a longer or shorter 

 period. The Cape gannet, which lays one egg, is an 

 instance of the former; and certain species of fran- 

 colins, which lay up to twenty eggs in a clutch, are 

 examples of the latter. Moreover, the young of 

 praecocial birds do not require nearly so much care 

 on the part of the parents as do the birds of the altricial 

 division. The size of the egg usually depends upon 

 the size of the bird, but not always. The eggs of the 

 Cape thrush (Turdus olivaceus), for instance, are 

 larger than the majority of the eggs of birds of similar 

 size, but these are exceptions to the general rule. 

 The colour of the egg is caused by pigment which is 

 deposited on it when the shell is forming within the 

 bird. In some birds the colours are in the shell 

 substance and on the surface. This is due to the 

 deposition of the colour during the whole time the shell 



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