Falcons are much less likely to attack a tight flock than a single bird indeed, "stragglers" slightly out of the starling flock formation are often taken by peregrines. Starlings normally fly in loose flocks (left), but when under attack by a peregrine falcon, they fly as close together as possible (right). Tight flocking is a response specific to the peregrine and is not employed (Little wonder that falconers and their dogs find it extremely difficult to get small birds to fly when a peregrine is "waiting on" overhead! On occasion, game birds allow themselves to be overtaken on the ground by dogs in preference to taking to the air and risking the falcon's deadly stoop.) Starlings normally fly in loose flocks, but when a peregrine is sighted, often at a considerable distance, they quickly assume a very tight formation (Figure 15.1). Large prey are allowed to fall to the ground and eaten there, but smaller items may be carried away in the air. Most prey are killed instantly by the sudden jolt of the peregrine's talons. Diving peregrines have been estimated to reach speeds of over 300 kilometers/hour (nearly 100 meters/second!). When a potential prey is sighted flying along below, the peregrine closes its wings and dives or "stoops." To make its ambush most effective, the falcon often "comes out of the sun" at its prey. Peregrines have exceedingly keen vision foraging individuals climb high up into the sky and move across country. These falcons take other birds as large as themselves nearly all prey is captured on the wing and in the air. The peregrine is a magnificent bird-eating hawk whose hunting behavior must be seen to be fully appreciated. One of my favorite examples of the joint adaptations of a predator and its prey is provided by the starling and the peregrine falcon. Many prey organisms recognize their predators at some distance and employ appropriate avoidance tactics well before the predator gets close enough to make a kill this behavior in turn has forced many predators to hunt by ambush. Prey have equally elaborate predator escape mechanisms, such as the posting of sentinels, predator alarm calls, background color matching, and thorns. Other examples include the rapid and very accurate strikes of predators as diverse as praying mantids, dragonflies, fish, lizards, snakes, mammals, and birds. Consider, for instance, the complex social hunting behavior of lions and wolves the long sticky tongues and accurate aim of some fish, toads, and certain lizards the folding fangs and venom-injection apparatus of viperine snakes spiders and their webs the deep-sea angler fish and snakes such as boas that suffocate their prey by constriction. Long-term evolutionary escalations of this sort have resulted in some rather intricate and often exceedingly complex adaptations. Hence, in the evolution of a prey-predator relationship, the prey evolves so as to dissociate itself from the interaction while the predator continually maintains the relationship. Obviously, these two selective forces oppose one another as the prey become more adept at escaping from their predators, the predators in turn evolve more efficient mechanisms for capturing them. Thus, selection on the prey population favors new adaptations that allow prey individuals to avoid being found, caught, and eaten. However, members of the prey population that are better able to escape predators should normally be at a selective advantage within the prey population. Hence, natural selection acting on the predator population tends to increase the predator's efficiency at finding, capturing, and eating its prey. Individual predators that are better able to capture prey should have more resources at their disposal and should therefore normally be more fit than those that are less proficient at capturing prey. In contrast, competition is a symmetric process in that both species are affected adversely and, where possible, each tends to evolve mechanisms whereby the relationship with the other is avoided. It is directional in the sense that one member of the pair (the predator) benefits from the association while the other (the prey) is affected adversely. Predation is often readily observed and easily studied, and neither its existence nor its importance in nature is doubted.
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