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For some animals, Halloween costumes last all year

Posted: October 27, 2011 - 11:01pm

TIP: Looks can be deceiving, so watch for movement or listen for giveaway sounds to find masters of disguise.

Hiking the hillside above the Dan Moller cabin, a small explosion almost at my feet spooked me so much I stumbled. A split second later (after losing about a week off my life), I recognized the pounding wingbeats of a grouse. It had been resting just a few feet away, but the complex pattern of brown, black, and white on its feathers had camouflaged it completely against the vegetation.

The word camouflage is a recent edition to the English language. Borrowed from the French “camoufler,” which means to disguise or conceal, it first became widely used in English 1917, during World War I. The development of accurate, long-range rifles as well as the use of aircraft generated the need to cover up people and equipment. Early military camouflage relied heavily on inspiration from the experts: animals.

Camouflage is a widely used survival tactic in the natural world. Animals utilize a spectrum of color and behavioral tricks to outwit predators or find prey. The basic premise of camouflage is simple: blend into the background, or disguise yourself as something or someone else. This can include color and patterns or stealing the physical identity of another creature or plant, even to the point of acting like something else.

Coloration is the most basic form of camouflage. One nickname for grouse is “fool’s hen,” because the bird may allow you to approach close enough you could almost touch it. It isn’t foolishness though. The grouse relies on its cryptic coloration — the intricately mottled patterns on its feathers that allow it to merge with its surroundings — as its first line of defense against predators. Movement attracts attention and breaks the bird’s cover, so it freezes in place as long as possible. The sudden loud noise of a grouse’s wingbeats as it takes flight startles a predator (or hiker) for that critical instant the grouse needs to escape. For all the grouse you see, who knows how many you walked past?

Why does the grouse’s camouflage work? Patterning is an important part of color camouflage. Patterns break up the outline of an animal so it’s harder to pick out from the background. The colors of the pattern sometimes give clues to who an animals’ main adversary is. For example, the main animals tigers prey on have limited color vision and can’t distinguish between orange and green. That’s where the pattern kicks in. The tiger’s slightly uneven stripes resemble the vertical shadows of tall grass; the alternating dark and lighter colors interrupt the outline a tiger presents, allowing it to creep closer to its meal.

Zebras also have stripes, but use them in a slightly different way. Their main predators are lions, which can’t see color; contrast is the zebras’ main defense. Zebras are herd animals, finding safety in crowds. The broken outlines presented by the stripes make it very difficult to distinguish where one animal starts and another begins in the chaos of a thundering herd of zebras on the run. This confusion of stripes makes it harder for predators to single out an animal to pounce on.

Countershading is another style of color camouflage. You may have observed animals, such as Sitka black-tailed deer, that have a light-colored underside. This would seem to be an attention-grabbing color scheme, but it’s actually quite stealthy. For a solid-colored animal, such as a moose, light from above creates a shadow underneath. This emphasizes the moose’s three-dimensional shape, distinguishing it from the surrounding brush or forest. For deer, which rely more on concealment than their larger cousins, a white belly brightens the shadows. This effectively flattens the deer’s outline, canceling out the shadows that might betray it.

Some creatures take cryptic coloration to a whole new level by having a body shape that mimics leaves, bark, or other objects. Insects and fish are the maestros of this method. For example, praying mantises come in a multitude of bizarre shapes. They ambush their prey, hiding in plain sight with their stolen identities. Some have weirdly sculpted shapes on the head and body to resemble crumpled dead leaves. Flower mantises are a group that lurks in tropical flowers. They often have wide legs and sometimes petal-shaped wings. The orchid mantis can be a delicate pink or white, and arches its abdomen over its back to look like the convoluted flower of its host.

For some animals, one color isn’t enough. The chameleon, with its ability to change colors, is the rock star of the camouflage world. The irony is that researchers think that changing colors may be as much for communicating with other chameleons as for camouflage. Think of it as a complicated set of blushes that show different emotions. For example, the lizards tend to be darker when angry or threatening intruders, while males trying to impress a lady go for multi-colored patterns.

Chameleons have a transparent outer layer of skin, with specialized cells called chromatophores in layers underneath. The upper layer of chromatophores has yellow and red pigments, while below that are cells that contain a substance that reflects blue. Even deeper are cells that contain the pigment melanin, which controls how “light” the colors appear. By combining these different layers for a variety of colors, the chameleon can express itself or disappear.

The most accomplished master of subterfuge is not the chameleon; the mimic octopus, discovered in 1998, has stolen that title. Many octopuses can change colors and patterns in an instant through chromatophores in their skin, allowing them assume the identity of rocks, corals, seaweeds or anything else they see. Octopuses can also manipulate their skin texture. An octopus can use muscles to deliberately make goosebumps on its skin; some species can even fine-tune bumps to resemble the knobby leaves of seaweeds.

The mimic octopus goes one step beyond just color and texture: it alters its behavior to impersonate other animals. It may flatten its body and undulate just above the ocean floor, with arms trailing behind it, imitating a sole (a kind of flatfish). It may make a costume change to bold dark and light stripes and swim with arms held stiffly out, pretending to be a poisonous lionfish. Or it might bury six arms and extend the other two so it looks like a sea snake, which has highly toxic venom.

This YouTube video shows some of the identities the mimic octopus assumes: www.youtube.com/watch?v=t-LTWFnGmeg&feature=related.

Observers have counted 15 species in the mimic octopus’ repertoire. Not only does the octopus have to remember what other animals look like and how they move, it also seems to know which of its alter-egos will frighten off its own predators. They may be spineless, but the mimic octopus is a mastermind of disguise.

• Beth Peluso is a freelance writer, illustrator, and avid birder. She enjoys spying on wildlife around Alaska.

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