CHAPTER XV 



BIRDS AND THE WEB OF LIFE 



§ I, Nutritive Inter-relations. § 2. Waves of Life. § 3. Reproductive 

 Inter-relations. § 4. Parasites of Birds. § 5. Strange Linkages. 

 § 6. The Hand of Man on Birds. § 7. The Inter-linking of 

 Lives. § 8. The Conservation of Birds. 



One of the great contributions Darwin made to science — 

 and to man's way of thinking in general — was the concept 

 of the web of Hfe. Animate Nature is a vast system of Hnk- 

 ages ; the circle of one life intersects that of another ; nothing 

 lives or dies to itself. There has been evolved a complex 

 system of inter-relations. As the philosopher Locke says, 

 nothing is by itself, everything is a retainer to some other 

 part of nature. How is this central biological idea illus- 

 trated in regard to birds ? 



§ I. Nutritive Inter- Relations 



Carnivorous birds, like hawks and owls, play an important 

 part in the economy of Nature by keeping a check on the 

 increase of small mammals, such as rats, mice, and voles. 

 Some of the plagues which spell ruin to man's farming and 

 foresting are in part the nemesis of short-sighted or selfish 

 destruction of birds of prey. 



It must be admitted, of course, that birds do not confine 

 their attention to mammals which are harmful from man's 

 point of view, such as the rodents. An owl will devour 

 a mole, and there would not be much need of mole-catchers 

 if man had not interfered with the gradually established 

 — though ever-oscillating — balance by shooting down 

 birds of prey. It is plain, however, that rats and mice 

 and voles are much more likely to be caught than weasels 

 and shrews and moles. Therefore, birds of prey operate 

 in the direction of progressive evolution. For we cannot 



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