Predators and Prey – Background

What makes the fox clever and the deer swift, and why do both have a keen sense of smell?  Predators and prey face different challenges in getting their food. Predators must find their prey, chase and catch it, subdue it if it fights back, all before they eat it. Prey animals must forage for food cautiously, always on the lookout for predators. The anatomy and the behavior of predator and prey animals reflect each species’ needs and way of life.

Both predators and prey need keen senses, but the position of eyes and ears, the functioning of noses and sense of smell, can be very different. Predators tend to have eyes facing to the front, for locating and following prey as it tries to evade capture. Forward-facing eyes give good depth perception because their fields of view overlap, thus providing binocular vision. Prey species tend to have eyes placed more to the side of the head. This gives them a larger field of vision, though they cannot pinpoint an object in front of them as well. However, eyes in this position help the animal see to the front, side, and, in some cases, even behind without turning their heads. Owls, bobcats and weasels all have forward facing eyes, while deer, mice, and songbirds have eyes directed more toward the side. To remember this difference, it’s helpful to learn the rhyme: “Eyes on the side, born to hide; eyes on the front, born to hunt.”

Keen hearing is crucial for both predators and prey. As with eye position, predator ears tend to point forward. Foxes and bobcats have ears directed towards the front, an aid in pursuing prey. Rabbits and deer have large ears that swivel around to pick up sounds. Without turning their heads, they can listen to sounds from every direction.

The sense of smell is highly developed in most mammals, although we humans depend more on sight. Having a keen nose is an important adaptation for detecting prey or the presence of predators. Hunters of all species learn the importance of approaching their prey from downwind, or their chances of getting close enough for a kill are slim.

Smaller predators, like weasels and housecats, frogs and fish, insects and spiders, are also prey to larger animals, and they must hunt for food and be on the lookout for their predators as well, a double challenge. They need the tools and skills of a predator as well as those of prey.

The behavior of predators and prey are largely instinctive, adaptations for their particular way of life, though learning and experience are often important, too. Predators tend to be inquisitive about their environment, restless and on the prowl. They investigate every nook and cranny in search of prey. Prey animals tend to stay within a well-known home range, foraging in familiar places and staying close to shelter.

Predators have a variety of different strategies for hunting. Some use ambush, lying in wait near a known game path and then pouncing on the unsuspecting prey. Rattlesnakes nose out rodent trails and curl up beside them to wait. Hawks and owls often hunt from perches. Other predators hunt more actively, searching high and low until prey is spotted and then chasing it down. The tracks of a weasel in the snow show an animal that dashes every which way as it hunts for mice. Dragonflies dart about catching mosquitoes, and otters lunge after small fish, newts, and frogs. Some predators stalk their prey. A bobcat crouches low and inches forward, gradually closing in on a hare. Its only chance is to get within striking distance before being spotted by the prey. Cooperative hunting helps some predators capture prey. Coyotes in a pack take turns leading the chase after a deer, or a pair may split up to cut a woodchuck off from its escape route. River otters sometimes cooperate in herding fish into coves where they can pick them off more easily.

Similarly, prey animals have different strategies for confounding their predators. They stay close to shelter and learn all the escape routes in their territory. Because predators can see the slightest movement, prey animals often freeze when they suspect a predator is near. Many prey are agile and make evasive maneuvers when chased. Rabbits run in a zigzag pattern, fish dart away, and butterflies flit about, just out of reach. Some prey congregate in groups for safety. It is hard for a predator to single out one victim among many in a swarm of insects, a school of fish, or a flock of birds. In a herd of deer there are more eyes to see with, more ears to hear with, and more noses to sniff out a predator on the prowl. Deer wave their white tails to alert herd members of danger, an effective group defense. Mobbing of predators is common among birds like crows and blue jays, a way to annoy a hawk or owl and force it to leave.

In a contest between a predator and its prey, the outcome is never certain, for many factors come into play. Age, size, and health of both predator and prey can affect the result. Predators tend to take the old, the young, and the weak since they are easier to catch. A predator in the prime of life can take on larger or faster prey than it can when it gets older and slower. How hungry a predator is will also affect its tendency to pursue or give up the chase. A prey animal that is healthy and alert, familiar with its territory, and experienced with dodging its predators has a good chance of getting away. Successful predators and prey will be able to pass on their genes to their offspring. In this way, natural selection hones the behavior, skill, and physique of each species for survival.

Some prey species like meadow voles and snowshoe hares show cyclical changes in population numbers over time. Snowshoe hare populations in Canada have a ten year cycle of low and high numbers. Because they reproduce quickly, the hare population increases rapidly until there is not enough food for them all, and then the population crashes. The population of lynx, the main predator of the hare, cycle as well, following the increases and decreases of the hare. Other prey species seem to fluctuate in less predictable ways, dependent upon many complex factors including weather, disease, predation, and food supply.

Even though it may seem cruel to us, predators need to eat to live, and they must kill other animals to do so. Predators play an essential role in an ecosystem, though this is often overlooked. In studies where predators were removed from an area, the prey tended to overpopulate, overgraze the vegetation, and suffer sickness and starvation. In Yellowstone National Park the reintroduction of wolves has resulted in a more balanced population of elk, healthier forests and streams, and greater biodiversity.

The lives of prey animals and their predators are closely linked, and over time, through their interactions, they improve each other. The swift falcon, light-footed deer, shy rabbit, and clever fox owe these characteristics to their ancestry and their roles as predator or prey.

Suggested Reading

Elbroch, Mark. Mammal Tracks and Sign: A Guide to North American Species. Mechanicsburg, PA: Stackpole Books, 2003.

Faccio, Steve. The Ups and Downs of Wildlife.  Northern Woodlands Magazine, 2007. http://northernwoodlands.org/outside_story/article/the-ups-and-downs-of-wildlife

Rezendes, Paul. Tracking and the Art of Seeing: How to Read Animal Tracks and Sign. 2nd ed. New York: Harper Collins, 1999.

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