II THE STRUGGLE FOR EXISTENCE 27 



the parents is killed ; while they ofter a defenceless prey to 

 jackdaws, jays, and magpies, and not a few are ejected from 

 their nests by their foster-brothers the cuckoos. As soon as 

 they are fledged and begin to leave the nest great numbers 

 are destroyed by buzzards, sparrow-hawks, and shrikes. Of 

 those Avhich migrate in autumn a considerable proportion are 

 probably lost at sea or otherA^se destroyed before they reach a 

 place of safety ; Avhile those which remain with us are greatly 

 thinned by cold and starvation during severe winters. Exactly 

 the same thing goes on with every species of wild animal and 

 plant from the lowest to the highest. All breed at such a rate, 

 that in a few years the progeny of any one species Avould, if 

 allowed to increase unchecked, alone monopolise the land ; 

 but all alike are kept within bounds by various destructive 

 agencies, so that, though the numbers of each may fluctuate, 

 they can never permanently increase except at the expense of 

 some others, which must proportionately decrease. 



Cases showing the Crreat Potuers of Increase of Animals. 



As the facts now stated are the very foundation of the 

 theory we are considering, and the enormous increase and 

 perpetual destruction continually going on require to be kept 

 ever present in the mind, some direct evidence of actual cases 

 of increase must be adduced. That even the larger animals, 

 which breed comparatively slowly, increase enormously when 

 placed under favourable conditions in new countries, is shown 

 by the rapid spread of cattle and horses in America. 

 Columbus, in his second voyage, left a few black cattle at St. 

 Domingo, and these ran ^vild and increased so much that, 

 twenty-seven years afterAvards, herds of from 4000 to 8000 

 head were not uncommon. Cattle were afterwards taken 

 from this island to Mexico and to other parts of America, and 

 in 1587, sixty- five years after the conquest of Mexico, the 

 Spaniards exported 64,350 hides from that country and 

 35,444 from St. Domingo, an indication of the vast numbers 

 of these animals which must then have existed there, since 

 those captured and killed could have been only a small portion 

 of the whole. In the pampas of Buenos Ayres there were, at 

 the end of the last centiuy, about twelve million cows and 

 three million horses, besides great numbers in all other parts 



