| MadSci Network: Zoology |
The short answer to your question is: yes, it is true. There's a lot of interesting material on hibernation, so I'll go into a little more depth below.
"Hibernation" commonly refers to any decrease in physical activity, metabolic activity, and body temperature over a winter season. Many animals hibernate, including bats, bears, skunks, mice, ground squirrels, many other rodents, and even some birds, and the state of hibernation is different for every group of animals. In scientific terms, the broadest distinction is between deep hibernation, in which the animal's body temperature drops to within a few degrees of freezing for a period of days or weeks, and torpor, in which the animal's body temperature declines, but usually doesn't go below about 15 degrees C. Animals in torpor generally remain inactive for shorter stretches of time than do deep hibernators -- some animals may enter a state of torpor on a daily basis. Bears, skunks, and other carnivores are not deep hibernators; their state of torpor is sometimes called carnivore lethargy. In all hibernators, though, the drop in body temperature is accompanied by a drop in heart rate and a drop in metabolic activity.
It's very hard to study hibernation, for several reasons. Laboratory studies that attempt to induce hibernation out of season have been almost entirely unsuccessful, and studies of animals entering hibernation are often difficult because the animal will tolerate only some kinds of measuring equipment. Successful studies show that the animal's body temperature declines either on a smooth curve, or in a series of steps. Once in a state of hibernation, the animal does not stay in that state until spring, but will periodically "wake up". As with hibernation itself, the triggers of this periodic arousal are not well understood. Some animals wake up to eat and drink; others (like the black bear) may go without food or water for over 100 days.
Bears rely on their fat reserves for nutrition during the winter. Because they are not eating, there is little buildup of nitrogenous wastes, and consequently, they neither urinate nor defecate during the hibernation period. The fecal plug that forms in the rectum at this time is called a tappen. Although the body temperature drops about 5 or 6 degrees, and the heart rate can drop to as low as 10 beats per minute (compared to a normal rate of 40 bpm), bears are still capable of coordinated movement while in this state, unlike deep hibernators and even some animals in a state of torpor.
For more information on hibernation, I recommend the book I found most of this information in: Hibernation and Torpor in Mammals and Birds, a collection of articles by Charles P. Lyman, John S. Willis, Andre Malan, and Lawrence C. H. Wang (Academic Press, 1982). On the web, there's a site about hibernation in bears (http://www.desktop.org/ygff/YGF.GrizInfoHib.html), and a great site with lots of general bear info: the Bear's Den.