Unit 3, Listening 1, Wild Survivors

 Wild Survivors

Narrator:       In the ruthless[1] world of survival, the battle for life and death takes on infinite forms. The endless struggle to eat and avoid being eaten has created weapon and defense systems that are continuously changing. The balance of power in nature is continually shifting. Sometimes it favors the hunter and sometimes the hunted. Those that are best at the game escape from the very jaws of death.

Adapting is necessary for survival. As conditions change—availability of food and water, temperatures, the presence of predators both animal and human—animals must change to meet the challenges or die.

Both weather and landscape[2] play a part in how animals adapt. Those that live must be well suited[3] to the demands of the environment. For example, the brown feathers of the ptarmigan, a bird about the size of a pigeon that lives in Europe and North America, make it almost invisible to predators. But the feathers serve another purpose as well—they protect the bird from the extreme cold by keeping its body heat next to its body, as well as keeping the cold air out.

The ptarmigan also grows long white feathers on its feet for the winter, which act like built-in snowshoes. Undoubtedly, the feathers also provide effective camouflage, a disguise[4] that helps the ptarmigan hide from predators by matching the color of its environment. When the snow disappears, so too do the white winter feathers of the ptarmigan. Its summer outfit, speckled grey and brown feathers, is well designed to suit the environment that is now free of snow. The young ptarmigans are in special need of good camouflage, since they cannot fly as well as the adults. They must protect themselves from predators by crouching and hiding among the rocks, moss, and wildflowers. Camouflage is virtually all the protection they have in the rocky landscape of the Pacific Northwest.

An even more elaborate survival system is found among the leaves of the oak tree, home to a variety of birds and a small, unimpressive-looking moth. In the springtime, the moth lays its eggs on the underside of the leaves, where they are less likely to be found by any hungry passersby. When the caterpillars hatch[5], they begin a dangerous journey. Those that survive make straight for the oak trees’ flowers. As they feed hungrily upon the flowers, they absorb the chemicals within them. This triggers a startling transformation. Quite literally, the caterpillar is what it eats. It can mimic the flowers superbly[6], even imitating[7] the movement of the flowers in the spring breeze.

Camouflage allows many of the caterpillars to mature, safe from predatory birds. But the story doesn’t stop there. In the summer, another set of caterpillars is hatched. By now, the flowers have fallen, and the caterpillars feed on the leaves instead. But there are different chemicals within the leaves now that set off a completely different reaction. This time, the caterpillars take on the appearance of the oak twigs[8], rather than the flowers. To its great advantage, the same species has shown a striking capacity for variation.

Adaptations can be remarkably specific to the environment. A praying mantis looks dangerously out of place on the forest floor, easy pickings[9] for any nearby predators. But a disappearing act takes place when the mantis reaches the flowers of the Asian orchid. So closely does it resemble its surroundings that the other insects sometimes search for nectar[10] on its body. Those that do may pay for their mistake with their lives.

The unbroken reaches of the desert seem to offer little in the way of protection or places to hide. Even here, though, natural selection has resulted in some very effective adaptations. The desert snake can transform itself from obvious to almost invisible in the sand, where it then hides in wait for potential prey. A lizard is no match at all for the deception of the snake.

The sandy bottom of the ocean floor can also hide its inhabitants. The Caribbean flounder, a fish whose flat body is the color of the ocean floor, makes good use of the seabed to hide from view. Only its eyes are left exposed to sight a likely meal. Its looks may be unusual, but they work superbly in these surroundings.

The pressure of natural selection, or survival of the fittest, is an irresistible force shaping all of nature. Those individuals who live to reproduce pass on their useful traits to succeeding generations. This is the essence of adaptation. As a general rule, the more closely you match your environment, the better your chances are of surviving. The genetic[11] combinations that result in camouflage like this, as well as the behaviors passed on from parents to offspring[12] by example, are the product of an unknowable number of hits and misses. Successful techniques and features live on in future generations, and unsuccessful ones necessarily pass away. It is one of the true miracles of nature.

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[1] ruthless: adjective hard and cruel

[2] landscape: noun wide open land

[3] suit: verb to be useful to

[4] disguise: noun something worn to change one’s appearance

[5] hatch: verb to come out of an egg, as a baby bird does

[6] superbly: adverb excellently

[7] imitate: verb to copy

[8] twig: noun a small branch

[9] easy pickings: noun phrase something obtained easily

[10] nectar: noun a sweet liquid from flowers

[11] genetic: adjective based on heredity

[12] offspring: noun children