"In the wild, plagues of excess population are a rarity. The seas are not crowded with sunfish; the ponds are not brimming with toads; elephants do not stand shoulder to shoulder over the land. With few exceptions, animal populations are remarkably stable. On average, of each pair's offspring, only sufficient survive to replace the parents when they die. Surplus young die, and birth rates are balanced by death rates. In the case of spawners and egg layers, some young are killed before hatching. Almost half of all blackbird eggs are taken by jays, but even so, each pair usually manages to fledge about four young. By the end of summer, however, an average of under two are still alive. Since one parent will probably die or be killed during the winter, only one of the young will survive to breed the following summer. The high mortality rate among young animals is an inevitable consequence of high fecundity. Of the millions of fry produced by a pair of sunfish, only one or two escape starvation, disease or predators. Half the young of house mice living on the Welsh island of Skokholm are lost before weaning. Even in large mammals, the lives of the young can be pathetically brief and the killing wholesale. During the calving season, many young wildebeeste, still wet, feeble and bewildered, are seized and torn apart by jackals, hyenas and lions within minutes of emerging from their mothers' bellies. Three out of every four die violently within six months."