Questions Readers Ask About Nature

Readers ask about bears and hibernation, greenhouse gases, how chameleons change color, and who owns America's forests.

  • NWF Staff
  • Aug 01, 1997
Nearly every day, we receive letters and e-mails from readers with questions about nature and the environment. Given your boundless curiosity about matters wild, we decided to make your queries--and our answers--a regular part of National Wildlife. So send your questions to: "Natural Inquiries," National Wildlife, 8925 Leesburg Pike, Vienna, Virginia 22184; or e-mail them to: Please keep in mind that our editorial staff is not equipped to answer every query; only those questions that are printed in the magazine will receive a response.

Do bears get out of shape during hibernation?

Bears may spend as many as seven months in their dens without eating, drinking, exercising or passing wastes. During that time, black bears, for example, survive by automatically cutting their metabolic rates sharply (their heart rate may drop as low as eight beats per minute) and living off accumulated body fat.

While hibernating, the nitrogen in the black bears´ urea is used to build protein. This not only prevents the bears from poisoning themselves with their own wastes, but it allows the animals to maintain their muscle and organ tissue through the winter. Even though they may lose as much as 30 percent of their body weight during the cold months, the creatures´ muscle mass remains intact. The bears emerge from their dens a little groggy and much thinner, but they´re not out of shape.

What are greenhouse gases and why are they important?

Gases in the atmosphere trap the sun´s energy and warm the Earth, acting much like the walls of a greenhouse--the so-called "greenhouse effect," which makes our planet livable. However, too much of a good thing can be dangerous. Carbon dioxide, chlorofluorocarbons (CFCs), methane and nitrogen oxides are all greenhouse gases produced from human activities. As more of these gases are released into the air from motor vehicles, power plants, factories and other sources, they can cause global warming--a gradual increase of average temperatures at Earth´s surface.

Most scientists agree that the mean global temperature has risen by at least one degree Fahrenheit during the past century. As a result, the distributions of some species appear to be changing. For example, researchers recently found that a North American butterfly species, Edith´s checkerspot, has been moving steadily northward over the past century. Conservationists worry that as such shifts take place, cold-loving animals and plants will be pushed into steadily shrinking ranges, and some may die off.

What are the advantages of using compact fluorescent light bulbs over standard incandescent bulbs?

The average incandescent light bulb is wasteful; about 90 percent of the electricity it uses is lost as heat and only 10 percent turns into light. New compact fluorescent lamps are much more efficient. One of these 18-watt bulbs produces as much light as the standard 60-watt bulb, and it typically lasts 10 times as long. While you initially pay more for the new bulb, it will save you as much as $50 in electrical bills and incandescent-bulb replacement costs over its lifetime. Perhaps more important, a compact flourescent bulb will generate less pollution from power plants during its lifetime of use than an incandescent bulb; as much as 1,500 pounds less carbon dioxide and 20 pounds less sulfur dioxide will spew into the atmosphere.

How do chameleons change color?

They have special cells called chromatophores in their skin. In response to signals from the creatures´ hormones and nervous system, pigments in these chromatophores move towards the surface of their skin. This shifting of pigments causes the skin to change color, and stripes or spots to appear or disappear. Often these shifts in hue are not intended to help the animals hide; rather, they scare away competitors or signal a willingness to mate.

Who owns America´s forests?

Nearly one-third of the United States--737 million acres--is forested. More than half of all forest lands--58 percent--is in private hands: Timber and paper companies own about 10 percent; other companies and individuals hold 48 percent. The remaining 42 percent is publicly held: Federal agencies control 34 percent, states manage 7 percent and local governments operate 1 percent.

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