Mark Baumgartner, age 9, of Dodge City, Kan., for his question:
HOW LONG CAN A BEAVER STAY UNDER WATER?
The beaver is known for his skill at cutting down trees with his strong front teeth. He lives in rivers, streams and fresh water lakes near woodlands. He is an excellent diver and swimmer and can swim underwater for up to a half mile at a time, holding his breath for about 15 minutes.
The beaver is actually a rodent. In fact, it is the largest rodent, or gnawing animal, in the world except for the capybara of South America.
Unlike roost other kinds of mammals, the beaver keeps growing throughout his life. Most beavers look larger than they really are because of their humped backs and thick fur. As it is, the beaver grows to be three to four feet long, including his tail. He weighs between 40 to 60 pounds.
Thousands of years ago, the beavers of North America were about seven and a half feet long, including the tail. No one knows why these huge beavers disappeared.
The beaver's small nostrils can close tightly to keep water out whit the animal is swimming underwater. He also has three eyelids over each eye. The two outer eyelids, one upper and one lower, fit around the eye. A transparent inner eyelid slides down over the eye and lets the animal see under water.
On land, the transparent inner eyelid protects the eye from sharp twigs when the animal cuts trees.
Actually, the beaver cannot see too well. He depends on his keen hearing and sense of smell to warn him of danger.
The beaver has wonderful teeth 20 of them. There are 16 back teeth used for chewing and four strong, curved front teeth for gnawing. The front teeth are called incisors and they have a bright orange outer covering that is very hard.
The back part of the beaver's incisors is made of a rather soft substance. When a beaver gnaws, this back part wears down much faster than the front part. As a result, these teeth have sharp, chisel like edges.
The incisors never wear out because they keep growing throughout the animal's life. The back teeth have flat, rough edges and stop growing when the beaver is about two years old.
There are large gaps between the beaver's incisors and his back teeth. Flaps of skin, one on each side of the mouth, fold inward and meet behind the incisors. These skin flaps seal off the back of the mouth. They let the animal gnaw wood on land or in the water without getting splinters or water in his mouth. The flaps open when the beaver wants to eat or drink.
The beaver's tail is stiff and flat and looks like a paddle. It is about 12 inches long and about seven inches wide. The beaver uses his tail to steer when he swims.
The beaver also uses his tail as a prop when he stands on his hind legs to eat or to cut down trees. Also, he slaps his tail on the water to make a loud noise to warn other beavers of danger.