CHAPTER XI 



NEST-BUILDING 



NEST-BUILDING had a very early origin and, as every one 

 knows, it is not confined to birds. Even fishes among 

 the lowest vertebrates are not wanting in builders of nests, and 

 the pile of leaves, sticks, and rubbish which the female alligator 

 heaps over her eggs, tier after tier, will at least compare favor- 

 ably with the mounds of earth raised by the Megapodes or 

 Brush Turkeys. If Audubon is correct, the bird is in this case 

 behind the reptile, for, according to his account, 1 the alligator 

 guards the premises with unusual ferocity, while the Megapode, 

 like the turtle, when the proper time arrives, deposits her eggs, 

 covers them, and goes her way, her "maternal instinct" being 

 perfectly satisfied by the performance of this simple duty. 



In that inbred pugnacity which characterizes the breeding 

 season of birds and higher animals generally, we possibly see the 

 origin of the instinct of incubation. The stages of its evolution 

 in the reptilian ancestors of birds may have been as follows: 

 first, burying the eggs, like the turtle or mound-building bird; 

 secondly, burying or concealing the eggs and guarding them, 

 the necessary warmth being furnished by decomposing vege- 

 table debris, as in the alligator, and not directly from the sun; 

 thirdly, laying the eggs and sitting over them to conceal as well 

 as to protect them, in a secluded place, the necessary heat now 

 being furnished by the body of the sitting bird. 



In the first instance, the eggs may not have been concealed 



1 " Observations on the Natural History of the Alligator," New Philo- 

 sophical Journal, vol. 2, Edinburgh, 1826-27. 



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