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One might suppose that trees finding competition in the forest so severe would be the first to take advantage of a clearing that men had made in or adjoining the forest and had abandoned after taking off a crop or two; their seeds are often carried to such clearings by birds, bats, terrestrial animals, or wind. But nothing of the sort happens; the trees that invade the new clearings are nearly all of different, fast-growing species that are rare in the forest, where they occur chiefly in openings made by the fall of a great tree. Only after the second-growth trees have profoundly changed conditions in the clearing do the true forest trees invade it; many years, probably centuries, must pass before the original forest is reconstituted.

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The forest trees not only compete with one another; they cooperate to create a favorable environment for themselves and all the lesser creatures that depend on them.

About the edges of this same forest over which I look, I find the courtship assemblies of male Orange-collared Manakins. These tiny, brisk birds compete pacifically for the females of their kind, who come to have their developing eggs fertilized. One might assume that each manakin's chances of winning a temporary partner would be better if he established his courtship station at a distance from his rivals, instead of within hearing, and often also within sight, of a number of them. But apparently this is not true, for perhaps the majority of the avian species that follow this mating system display in groups or assemblies rather than in isolation. They cooperate to establish an assembly that persists in the same locality year after year, and is large and conspicuous enough to be easily found by the females, at the same time that they vie intensely to attract the females visiting the assembly (Skutch 1992).

Examples of a similar mixture of cooperation and competition among humans are not hard to find. In a big city, shops that sell similar goods are often located close together on the same street or in the same section. Although they compete for customers, they likewise help one another by making it widely known that this is the part of the town where shoes, or jewelry, or whatever one wants, is to be found. In both nature and human society, opposites such as cooperation and competition, good and evil, beauty and ugliness, are so intricately intermixed that we must be wary of all sweeping generalizations.

Mutual Protection

One of the most widespread forms of mutual aid in the animal kingdom is cooperation in escaping enemies. Everywhere the milder birds and mammals appear to have formed defensive alliances to protect themselves from the fierce predators. When they spy an approaching hawk, birds give special cries, often loud and sharp, that cause others to fall silent and dive into the nearest available

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covernot only other individuals of their own species but likewise birds of other kinds, so that a hush falls over fields and groves as the raptor sails by.

Mammals and birds reciprocally warn each other of perils. While intensively studying Mule Deer in the Sierra Nevada of California, Thane Riney (1951) often saw the deer alerted to the approach of a person or some other dangerous animal by the alarm notes of birds that had noticed the intruder first. The birds, of several kinds, not only warned the quadrupeds of peril; by resuming their songs or other activities, they reassured the deer that the danger had passed, so that the latter returned to their grazing or undisturbed repose. By imitating appropriate notes of the birds, Riney could not only alert the deer but also allay their fears.

On the African savannas, Ostriches often associate with antelopes and other herbivorous animals. Because they are taller than most of the associated quadrupeds and have sharper eyesight, the birds often warn their four-footed companions of impending danger. It is probable, too, that they profit by the mammals' keener sense of smell, when the approaching predator is not in sight