- The Washington Times - Wednesday, November 24, 2004

The preservation crew found a little brown bat hibernating in the dome of the Jefferson Memorial two winters ago.

“Animals are hibernating all around, and people would never know it,” says Gopaul Noojibail, resource manager for the National Park Service, National Capital Region.

The staff, which has not found any hibernators before or since, brought the bat to Mr. Noojibail in a box.

“We warmed it up so it woke up completely and let it go. That’s what we could do,” he says. “What we hoped is it found another space quickly and went back to sleep.”

Hibernators, like the little brown bat, enter into a state of dormancy to survive the winter, selecting shelters safe from predators. They respond to changes in temperature, day length and quality or lack of food, a response that is not learned but is innate, says John Carnio, general curator for the Maryland Zoo in Baltimore.

The animals’ food supplies are reduced as the day length shortens and temperatures drop, leaving a cold, frozen ground inefficient for plant growth. Without hibernation, some animals would expend more energy searching for food than they would gain from the food they eat, if any, and others would not be able to maintain their body temperatures in the cold.

“The point is they’re trying to avoid a period of food shortage by allowing biochemical processes to go much slower,” says Randall Packer, professor of biology at George Washington University (GWU), about hibernators. He holds a doctorate degree in zoology. “They can get enough energy from fat stored in the body to live all winter long until growth occurs in the spring.”

Besides hibernating, animals adapt to winter by migrating, as do some bird species, or by adjusting to staying out in the cold conditions, like foxes, shrews, gray squirrels and wild turkeys.

Animals that do hibernate enter into different levels of dormancy. Deep hibernators, such as bats, chipmunks, woodchucks, turtles, toads and snakes that inhabit the metropolitan area enter into a state of inactivity for several days, weeks or months. Their body temperature drops; their circulation becomes limited; and their metabolism, heartbeat and breathing slows.

“If you picked them up, you would swear they were dead,” Mr. Carnio says.

Torpors, animals who hibernate for a short period of time overnight or for a few days, undergo a slowdown in their bodily processes that is not as extreme as the deep hibernators. Their body temperature drops to 59 degrees Fahrenheit (15 degrees Celsius), while the temperature of deep hibernators dips to as low as 41 degrees Fahrenheit (5 degrees Celsius), near freezing, Mr. Packer says.

Torpors — including bears, deer mice, skunks and raccoons that live in the Washington area — are able to arouse themselves during a stretch of warm weather in order to eat and remove waste materials.

Deep hibernators do not and remain in dormancy. However, if their body temperature dips too low, such as to 30 degrees Fahrenheit (-1.1 degrees Celsius), they will awaken and shiver until their bodies return to above freezing temperatures. They repress this shivering instinct when they enter into hibernation, Mr. Packer says.

Animals have an average body temperature of 100.4 to 104 degrees Fahrenheit (38 to 40 degrees Celsius) and humans, 98.6 degrees Fahrenheit (37 degrees Celsius), Mr. Packer says. Their body temperature remains the same when they sleep or are awake.

“Basically, they are shutting down their systems,” Mr. Noojibail says. “It’s not sleep. It’s much deeper than sleep. … There’s a lot less going on internally.”

Hibernation, unlike sleep that is needed for rest and recharging the body, is a physiological state an animal uses to save energy. Some hibernators sleep for longer and longer periods of time as the days shorten, and during one of their sleeps, enter into the hibernation state.

“It’s almost like they go into screen-saver mode all winter long,” says Kate Toniolo, outdoor recreation planner for the Patuxent Research Refuge, in Laurel, of the U.S. Fish & Wildlife Service.

Animals hibernate in one of two ways, either through predictive dormancy by responding to shorter day lengths — as do cold-blooded animals that need warmth from their environment to maintain body heat — or by consequential dormancy. The second type of hibernators respond to several consecutive days of cold temperatures at just above freezing or one night of temperatures below freezing during the first frost. In turn, the animals come out of hibernation with the first thaw in early spring.

“They can only store so much under their skin,” says Marc Allard, associate professor of biology at GWU, in Northwest. He holds a doctorate in zoology.

Hibernators prime for the onset of cold weather by the time shorter and colder days arrive, beginning their preparations in late summer that continue into the fall. Some bulk up by eating extra food that their bodies convert into two types of body fat.

Brown fat forms around the animals’ major organs to provide a quick burst of energy and warm the organs for the moment when the animal awakens from dormancy, Mr. Noojibail says. White fat, he says, is a general fat store that maintains the animal’s physiological system during this period of inactivity.

Other hibernators, such as deer mice, keep food in caches or stores. These animals bury food, such as nuts and acorns, that they can eat every few days between episodes of hibernating. Gray squirrels, which are non-hibernators, bury nuts in several locations to last them through the winter.

“In captivity, true hibernators will try to hibernate, but they need certain conditions to do that,” Mr. Carnio says.

Zoo staff watch the hibernators, including a black bear and a female polar bear if she is pregnant, to determine if they are showing signs of wanting to hibernate. The animals become more lethargic, engage in less activity, sleep longer and eat less.

In response, staff adjusts the animals’ living areas with changes in lighting and temperature that imitate their natural environments and by withdrawing the amount of food available for feeding.

Prairie dogs, also hibernators, live outdoors on the zoo grounds and respond to the natural environment to begin hibernation and do not need their environments adjusted.

“We try to provide conditions for animals to behave as naturally as possible,” Mr. Carnio says.

Out in the wild, short- and long-term hibernators stay in burrows, under logs, in the mud underneath a pond or lake, in holes and other openings in trees, in rocky outcrops and in caves — all places that are sheltered from the weather and from predators.

Gophers, or ground squirrels, do hibernate and prefer burrows, for example, and bats and bears, caves. Reptiles, such as frogs, snakes and turtles, like to burrow into the forest floor or the mud beneath a body of water.

“They’ll usually find a safe place where they won’t be disturbed,” Mrs. Toniolo says.

Humans should avoid bothering the animals, she says, since the animals may not have enough energy stores to survive the rest of the winter if they are awakened.

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