Wednesday, April 20, 2011

Biology Terms: Countershading By Gwen Nicodemus Diamond Quality Author Article Source:



Many marine creatures are countershaded, which is a type of camouflage for them. What exactly is countershading?

Imagine that you are in a boat on the ocean and looking down. The ocean water looks dark blue. If you were an animal in the ocean, what color should you be to hide from animals in the sky, or higher up in the ocean, than you are?

Now, imagine you are SCUBA diving on the bottom of the ocean floor and look up, toward the sky. During the daytime, the sunlight filters into the water. What color should an animal be so it can blend into the water and hide from the animals below it in the water?

Animals selected for countershading

Animals that are darkly colored on their top part and lightly colored on their underside are said to be countershaded.

Animals that are darkly colored on their top part, where their dorsal fins are located, are less likely to be found and eaten by sky creatures or ocean animals higher up in the ocean than they are. Their dark colored skin blends into the color of the ocean around them and they have higher survival rates than animals that are lightly colored on the top.



Animals that are lightly colored on their underside blend into the ocean better when looking from the ground upward. They are found and eaten less often by the fish and animals underneath them in the water, so they have better survival rates than animals with darker colored under sides.

So, animals with both of these features have an even better chance of living to an age that they can reproduce.

What kind of animals are countershaded?

Countershading of the type, where the animal blends into its background, is most prevalent with marine animals. Sharks, dolphins, porpoises, fish, and penguins all present this kind of countershading.

Another type of countershading has the same type of principles, but the animals don't blend completely into their background. Instead, their coloring makes it difficult for predators to see where their bodies start and end. Some lizards and caterpillars present this type of countershading.

What have we learned from the animals?

An artist and naturalist named Abbott Thayer studied countershading. He described and published his nature studies regarding countershading in 1892. In fact, sometimes countershading is called Thayer's law. Thayer made his contribution in World War I by suggesting that the military paint their ships using countershading techniques.

Countershading and camouflage techniques are used frequently by the military. Clothing fashions are also influenced by these types of color schemes.

I'm an engineer who quit full-time work and now freelance so I can homeschool my two children. I also teach science classes at a local homeschooling cooperative. As a temporarily retired engineer, I try to keep my brain active by reading, writing, and teaching. Check out the free resources, including unit studies, videos, tutorials, and little books at Unit Studies By Gwen or her blog at GwenOnline.
©2011, Gwen Nicodemus

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