Adaptations and Animal Behavior

Three kinds of adaptations

Biologists often sort adaptations into three kinds. A quick way to tell them apart is to ask what you would need to notice it: a look at the animal, a video of it, or a test of what is going on inside it.

Adaptations are inherited, so they are passed from parents to young. They build up over many generations through natural selection, which is covered on the Evolution and Adaptation page. This page is about what adaptations look like in action, especially the ways animals behave.

Camouflage

Camouflage is coloring or shape that makes an animal hard to see. It helps prey hide from predators, and it helps predators sneak up on prey. There are several kinds.

• Background matching is the most common kind. The animal's colors and patterns copy its surroundings. Flatfish such as flounders match the sea floor, and walking stick insects look like twigs.
• Countershading means dark on top and pale underneath. Light from above normally makes the top of a body bright and leaves the belly in shadow, which makes a round shape stand out. Countershading cancels that out. Many sharks are colored this way.
• Disruptive coloration uses bold stripes, spots, or patches that break up an animal's outline, so the eye can't find its edge. The mottled down of ptarmigan chicks is one example.

Some animals can change their camouflage. Arctic foxes grow a different coat for winter and summer, and many octopuses can change the color and pattern of their skin.

Warning colors

Not every animal tries to hide. Some are brightly colored on purpose, and the colors work like a sign that says "don't eat me." This is called warning coloration. Biologists also call it aposematic coloration.

The bright colors of a strawberry poison dart frog go with poison in its skin. A striped skunk's bold black and white matches its smelly spray. Monarch caterpillars eat milkweed, which contains poisons, and those poisons stay in the body of the adult butterfly. A bird that eats a monarch may throw up, and it tends to avoid orange and black butterflies after that.

Warning colors only work if predators can learn them. Each predator has to have a bad experience, or watch one, before it starts to steer clear.

Mimicry

In mimicry, one species looks like another. There are two main kinds, named after the 1800s naturalists Henry Walter Bates and Fritz Müller.

• Batesian mimicry: a harmless species looks like a harmful one. Many flies are striped like wasps or bees. One robber fly looks so much like a bumblebee that you have to look closely to tell them apart.
• Müllerian mimicry: two or more harmful species share the same warning pattern. Several kinds of bad-tasting Heliconius butterflies look alike, so predators only have to learn one lesson.

The viceroy changes sides

For most of the 1900s, textbooks used the viceroy butterfly as the classic Batesian mimic. It looks very much like the monarch, and people assumed it was a tasty fake. In 1991, David Ritland and Lincoln Brower tested that idea by offering birds pieces of viceroys, monarchs, and queen butterflies from Florida. The birds found the viceroys just as unpleasant as the monarchs. So the viceroy is now usually described as a Müllerian mimic: both butterflies are protected, and they share the cost of teaching birds.

Viceroys in other places may taste different, so scientists are careful not to say the whole story is settled. So even a famous textbook example can turn out to be wrong once someone actually tests it.

Instinct and learning

An instinct, or innate behavior, is one an animal can do the first time without being taught. A male three-spined stickleback, a small fish, grows a red belly in breeding season and attacks other males with red bellies. In tests, he would even attack a rough wooden model as long as its underside was red. Once a behavior like that starts, it runs to the end. Biologists call it a fixed action pattern.

Learned behavior changes with experience. Most animals use a mix of instinct and learning. Here are the main kinds of learning.

Insight is the hardest kind to prove. Köhler ran his chimpanzee tests about a century ago and thought the solutions came in a sudden flash. Other scientists have argued that the chimps may have picked up parts of the solution earlier, through play and practice. Telling "worked it out in its head" apart from "learned it bit by bit" is still tricky.

Imprinting has a real job in the wild. A duckling that sticks close to its mother is safer from predators. People have even used it to help rare birds: in some programs that raise young whooping cranes, keepers wear crane costumes so the chicks don't imprint on humans.

Migration

Migration is a regular journey from one place to another and back, usually with the seasons. Animals migrate to follow food, rain, or a safe place to raise young. Long journeys take lots of energy, so migration only pays off when the benefits are big.

• Arctic terns nest in the far north and spend the northern winter in the seas around Antarctica. In 2010, scientists fitted 11 terns from Greenland and Iceland with trackers weighing 1.4 grams. The birds averaged about 71,000 km in a year, and some flew more than 80,000 km. Because terns can live for 30 years or more, one bird might fly over 2 million km in its life. That is a careful estimate, not a measurement of one bird.
• Eastern monarch butterflies fly south in the fall, some as far as about 3,000 miles (4,800 km), to spend the winter in fir forests high in the mountains of central Mexico. No single butterfly makes the whole round trip. The trip north in spring takes three or four generations, so the butterflies that arrive in Mexico each fall have never been there before.
• Wildebeest in the Serengeti and Masai Mara of East Africa, more than a million of them, move in a giant loop that follows the rain and fresh grass. Calves are born on the southern plains early in the year, and the herds move north toward the Mara River during the dry season, then back south. How far is that? It depends on what you measure. One textbook says the herds travel over 1,800 miles a year. GPS collars on 62 wildebeest measured the route between their wet-season and dry-season ranges at about 130 km on average, and the animals wander a lot along the way, so the total walked in a year is much longer than that.

Some animals must migrate every year. Others migrate only in some years. Some owls that live on the tundra, for example, move south only when food runs short.

Finding the way

How does a young bird or a butterfly find a place it has never seen? Animals use several cues, often more than one at once. Scientists are still working out many of the details.

Getting through hard seasons

Instead of leaving, some animals stay put and slow down. When food is scarce or the weather is too cold, hot, or dry, slowing the body saves energy. There are four main words for this, and they mean different things.

Are bears true hibernators?

Bears are the classic picture of hibernation, but they caused an argument. Hibernating animals usually let their body temperature fall. A black bear's drops only a few degrees, so some scientists used to say bears were just in a deep sleep. Then, in 2011, a team measured black bears through the winter. For five to seven months the bears didn't eat, drink, pee, or poop. Their metabolism fell to about a quarter of normal, and their heart rate dropped from about 55 beats a minute to as few as 9. Body temperature stayed between about 30 and 36 °C. Most biologists now say bears do hibernate, just in their own way. Mother bears even give birth to cubs in the den during winter.

Living in groups

Many animals live in groups, and communication holds the group together. Animals send signals with chemicals, sounds, sights, and touch.

Honeybees: the waggle dance

When a forager bee finds good flowers far from the hive, she comes home and dances on the upright honeycomb, in the dark. Her dance is a figure eight: a straight run through the middle, then a half-loop back to the start on one side, another straight run, and a half-loop back on the other side. In the straight middle part, the waggle run, she shakes her body from side to side. Inside the hive, straight up on the comb stands for the direction of the sun. If the flowers lie 40 degrees to the right of the sun, she tilts her waggle run 40 degrees to the right of straight up. The longer the waggle run lasts, the farther away the flowers are. For flowers close to the hive, bees use a simpler round dance instead.

Ants, wolves, meerkats, and elephants

• Ants talk mostly with chemicals called pheromones. An ant that finds food leaves a scent trail on the way home, and nestmates follow it to the food.
• Wolves live in packs, and a typical pack is a family: a mother and father wolf and their young of the last few years. The parents lead. The old idea of an "alpha" fighting its way to the top came mostly from studies of unrelated wolves kept together in captivity.
• Meerkats take turns as sentinels. While the others dig for food, one stands on its hind legs or climbs a bush and keeps watch. Their alarm calls differ for a hawk overhead and a jackal on the ground, and they also signal how urgent the danger is.
• Elephants live in family groups led by an older female, the matriarch. In one study, families with older matriarchs were better at telling the calls of strange elephants from familiar ones, and they raised more calves. It seems the whole family benefits from what the oldest female remembers.

Who figured this out?

The study of animal behavior in nature is called ethology. Here are a few milestones. Dates for early observations are approximate.

Key words

• Adaptationan inherited trait that helps a living thing survive and reproduce where it lives
• Structural adaptationa body part, shape, or color that helps an animal survive
• Behavioral adaptationsomething an animal does that helps it survive
• Physiological adaptationchemistry or a process inside the body that helps an animal survive
• Camouflagecoloring or shape that makes an animal hard to see
• Countershadingdark on top and pale underneath, so the body looks flat
• Warning colorationbright colors that signal an animal is poisonous, bad-tasting, or dangerous
• Batesian mimicrya harmless species looking like a harmful one
• Müllerian mimicrytwo or more harmful species sharing one warning pattern
• Instincta behavior an animal can do without learning it
• Imprintingquick learning, early in life, of who to follow
• Migrationa regular journey between places, usually with the seasons
• Hibernationa long, deep winter rest with a much slower body
• Torpora short slowdown, lasting hours or days
• Estivationa slowdown to survive heat or drought
• Pheromonea chemical signal sent from one animal to others of its kind

Game: Name that Adaptation

Read each card and decide what kind of adaptation it describes. Structural means a body part, shape, or color. Behavioral means something the animal does. Physiological means chemistry or a process inside the body. Each correct answer earns 1 point, and your best score is saved on this device.

Quick quiz

Six questions. Pick one answer for each, then press Check my answers.