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By Root 555 0

biocompatible association, but on the contrary prey, often heavily, upon the members of such associations. Because many of them are big and powerful, they frequently excite humans' misplaced adulation of bigness and power (a major cause of their misfortunes), and not a few win admiration by their grace or beauty. Contributing little or nothing to the support of the living community (except its scavengers), they make heavy demands upon it. If not deliberately trying to reduce their numbers, a conservation program committed to biocompatibility rather than undefined biodiversity should at least stop spending all the money and effort now given to their protection and increase.

One of the gravest mistakes of wildlife management in our time is the reintroduction of predatory birds and mammals into areas where they have long been absent, such as the artificial establishment of Peregrine Falcons in cities. The undesirable, often

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disastrous, effects of introducing alien animals, even some admirable in themselves, into countries like Australia, New Zealand, and the United States have long been recognized and deplored. Reintroduction of large and dangerous species may become equally deplorable.

Predation is widely viewed as indispensable to prevent populations of animals becoming so numerous that they destroy their habitats, "eating themselves out of house and home." Even those who condemn predation as a major evil, a lamentable miscarriage of evolution, may grudgingly concede that it is a necessary evil. Nevertheless, the role of predation in regulating animal populations has been exaggerated. It is most obviously necessary in the case of large browsing and grazing quadrupeds-deer, antelopes, horned ruminants, elephants, and the likewhich may so severely overexploit light woodland or grassland that it may take years to recover after the exploiters' numbers are reduced by widespread starvation. Where elephants are protected, they become too numerous and so damage their range that, despite sentiment, their herds must be culled to avert disaster. Shooting of excess individuals by expert marksmen is kinder than the methods of predators, which too often tear the flesh of still living victims.

When we turn to frugivorous and insectivorous birds, we find a very different situation. It is hardly an exaggeration to say that they are incapable of ruining their habitats. In an unfavorable season, fruits may become so scarce that hungry birds are reduced to eating them before they ripen, when they are harder to digest and less nourishing but may already contain viable seeds. The birds' reproduction may be depressed, and some may starve; but the fruit-bearing trees and shrubs will not be injured by premature removal of their fruits, and next year they can yield abundantly. Similarly, nectar drinkers can hardly injure flowering plants, even if, as sometimes happens, they damage flowers by piercing or tearing corollas to reach the sweet fluid. When nectar is scarce, they may turn to insects, as hummingbirds frequently do. Insectivorous birds can rarely glean so effectively that they exterminate the insects, spiders,

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and other small invertebrates that nourish them. With their rapid reproduction and reduced pressure upon them, they soon restore their populations and continue to support the insectivores.

Birds can regulate their populations without outside intervention. A widespread method is territoriality, which adjusts the number of breeding pairs to the areas and resources adequate for rearing their broods. The size of broods is correlated with the longevity of adults. At latitudes where the rigors of winter or the hazards of long migrations to escape winter reduce life expectancy, broods are substantially larger than are those of related species at low latitudes, where the average life span of resident birds is considerably longer. In contrast to mammals, which often begin to reproduce before they cease growing, many birds delay breeding for one or more years after they are full-grown.