CHAPTER XI 



PARENTAL CARE AND NEST-MAKING 



§ I. Incubation. § 2. Nest-making. § 3. Feeding the Young. 

 § 4. Educating the Young. § 5. Defence of the Young. § 6. The 

 Case of the Cuckoo. § 7. The Case of the Mound-Birds. 

 § 8. Social Life. § 9. Retrospect on the Evolution of Parental Care. 



Compared with most fishes and amphibians, and even 

 with most reptiles, birds show a marked reproductive 

 economy. The practicabihty of this has depended on an 

 associated increase of parental care. It has not been proved 

 that reduction of reproductivity is the direct physiological 

 consequence of an intensification of life, or, to use Herbert 

 Spencer's phraseology, that the reduction of genesis is the 

 result of heightened individuation. What may be safely 

 said is, that a successful line of evolution was entered upon 

 when certain birds varied more or less simultaneously in the 

 direction of reduced reproductivity and in the direction of 

 parental care. Reduced reproductivity left more energy 

 free for other ways of disposing of it, but it would have been 

 a hazardous experiment if it had not been associated with 

 increased parental care, which implies reduced infantile 

 mortality. 



There is another way of looking at the matter. When the 

 chances of life are heavily against survival, e.g. when enemies 

 are very numerous, the spawning solution is often quite 

 effective. Only a few oyster embryos survive out of a million, 

 but the race of oysters continues because the oyster produces 

 so many millions. Parental care is at once unnecessary and 

 impossible. When parental care made economised repro- 

 ductivity possible without endangering survival, it likewise 

 made its own growth more possible. With fewer offspring, 



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