- The Washington Times - Wednesday, July 30, 2003

Some use stripes, others wear dull shades, and a third can change its colors on a dime. Animal camouflage comes in many varieties, but the goal is universal — to increase life expectancy.

“Basically, animal camouflage has evolved to increase the fitness of the individuals that possess [it],” says Gary Graves, a curator of birds at the Smithsonian’s National Museum of Natural History. He holds a doctorate in biological science. “If you’re hard to detect, you’re more likely to survive.”

A common form of camouflage is an animal’s ability to match its surroundings, says Jim Parkhurst, associate professor of wildlife science at Virginia Tech.

A brownish squirrel, for example, blends well into the trunk of a tree it may be traversing, while a stonefish is almost identical to the ocean floor where it lives.

The same goes for tuna and other fish, such as the local silverside, which has a darker shade on top and a lighter belly. This color scheme makes it hard for predators to detect them, from below and above. Their pale bellies look like the water’s surface to predators that are looking up from below, and for birds, which are looking down at the fish, their backs look like the surrounding ocean.

Another camouflage tactic is mimicry, says Jeff Williams, collections manager of fish at the museum.

“Some fish mimic other fish that are associated with venom glands,” says Mr. Williams, who holds a doctorate in zoology. “They do it for protection.”

The poison-fang blenny, which resides in the Indian and Pacific oceans, is a fish that nonpoisonous blennies mimic by developing the poisonous fish’s color pattern, Mr. Williams says. The poison-fang blenny looks different in different areas of the world. In Fiji, for example, it’s bright yellow. The local nonpoisonous blennies mimic whatever the local poisonous blenny looks like, he says.

Another famous imitator is the walking stick insect, which looks like a twig.

Another type of camouflage is what zebras have, a type of coloration that distorts the look of the animal, says Mr. Parkhurst, who holds a doctorate in forest resources. To a predator, like a lion, when zebras stand together in a group, they can look like one big animal instead of a group of animals. So this type of camouflage doesn’t hide the animal, it misrepresents it.

The appearance of some animals changes along with the seasons, Mr. Parkhurst says.

“The snowshoe hare, which we have in the Appalachian highlands, changes with the seasons,” he says. “In the summer it’s brown, and in the winter it’s white, enabling it to blend in with its environment.”

The male scarlet tanager, a local songbird, is black and a brilliant scarlet in the mating season. In the fall, the scarlet plumage gives way to a duller olive yellow, the color of the female.

“They look so different that the uninitiated might think there were two different species involved,” Mr. Graves says.

Birds and mammals whose plumage and fur change colors depending on the season usually get their cue from the daylight hours, Mr. Graves says. When the nights start getting longer, they lose the summer coat, which may be gray, as in the snowshoe hare’s fur, and get their winter coat, which may be white.

Other animals get their cues from immediate threats in their surroundings. Many lizards are able to change their color, usually from darker to lighter shades or vice versa, by either contracting or expanding the cells that contain pigment called melanin, says Kevin de Queiroz, a curator in the division of amphibians and reptiles at the museum.

The contraction or expansion of those cells occurs when there is a hormonal change in the body, which can be triggered by threats in the environment.

“It would be like us having an adrenaline rush,” says Mr. de Queiroz, who holds a doctorate in zoology.

A lizard that can be found in North Carolina called the green anole has the ability of contracting and expanding its melanin-containing cells, Mr. de Queiroz says.

“The anole lizards can change from green to brown,” Mr. de Queiroz says. “If you see them on the ground, they are usually green, but if you pick one up, they will turn brown.”

These and other lizards change color in response to several factors, Mr. de Queiroz says.

“It can be fright or stress or daylight,” he says.

Because lizards don’t regulate their body temperature internally, like humans, they rely on outside stimuli to do so. When the temperature drops, the lizards adopt their darkest shade to be able to absorb as many of the sun’s rays as possible.

“And then when it’s hot, they become lighter so they can reflect more,” he says.

Some lizards and amphibians use color change not only to hide, but also to attract females during the mating season, much as birds do.

“They kind of have the best of both worlds. They can expose flashy colors or they can show a duller color, which allows them to hide,” Mr. de Queiroz says.

If camouflaging is so beneficial, why are there still animals that don’t have camouflage?

“Those that don’t use camouflage make behavioral changes,” Mr. Parkhurst says. “They might start becoming more elusive, or they might become nocturnal.”

Members in the rodent group, such as mice, for example, often are nocturnal to escape their predators, he says.

“But it’s not enough [to escape] an owl, because they have such excellent eyesight,” he says.

So, whether animals make behavioral changes or use camouflage, the goal is always the same: survival. In some cases the traits that improve survival have taken millions of years to evolve, Mr. Graves says.

“Any trait that allows you to pass on more offspring to the next generation will increase your ‘fitness,’” he says. “It’s part of the natural selection.”


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