Winter Survival

Winter Survival

Judi Manning

We don more layers of clothing as the temperature plummets. Some birds migrate as the day length shortens and before it gets very cold. Pygmy Nuthatches snuggle tightly to keep warm during a sub-zero storm. In late fall, Ruffed Grouse grow 'snowshoes' -- comb-like structures (pectinations) on each side of the toes -- to help them walk more easily across the snow. The Chickadee and Tufted Titmouse fluff their outer contour feathers, trapping insulating layers of air between the soft down feathers near their body. Their winter plumage consists of 25% - 30% more feathers than in the summer. Their heartbeat and breathing rate slow and the body temperature drops nearly 20° (to 108°) as they sleep in an energy conserving, temporary state of hypothermia. Bobwhites roost in a circle to fight off the winter chill.

Moths and butterflies pupate into a state of dormancy wrapped in their silk cocoon. Fish, if the oxygen is cut off because the lake is too shallow will die. Many turtles burrow in the mud at the bottom of the pond or lake. In the fall, baby painted turtles hatch in their underground nests and freeze along with the sandy surroundings. In the spring they thaw out, dig to the surface, and crawl away. Birds and animals will starve if too much snow or ice covers the food. Toads dig down into the ground as far as three feet.

The hairs on a deer are hollow and filled with air to provide insulation from the cold. The soft fine hair next to their body acts like thermal underwear. The squirrel in search of food, keeps his tail flat against its back and neck to protect it. A sleeping Red Fox wraps its tail around its head like a muff. Arctic foxes have the warmest fur of any animal in the world.

Snowshoe hares, grow fur up to an inch thick on the soles of their feet to provide warmth and skid-proof shoes.

The snowshoe hare and several members of the weasel family acquire a white winter coat to make them invisible to predators against the snow. To escape from hawks and owls, Ruffed Grouse sometimes plunge head first into a snow bank and remain hidden for days. Mice and shrews spend their entire winter in an underground network of tunnels. These tunnels provide warmth, security, and a pathway to food sources. Ants build year—round nests made up of many chambers and deep underground tunnels that extend below the frost line. They hibernate huddled together in the special chambers away from the dampness and changing outside temperatures until spring arrives.

HIBERNATION Many animals survive the winter by hibernating. Research indicates hibernating animals generate a chemical that drops their body temperature 10° and slows their heartbeat.

There are two kinds of hibernation:

(1) True hibernators have a few heartbeats per minute and their body temperatures are slightly higher than their surroundings.

CHIPMUNKS, GROUND SQUIRRELS, MARMOTS AND WOODCHUCKS are true hibernators. Their bodies cool down until they are close to freezing, or "going into torpor" for 5 - 7 months. They stay torpid (sleeping state) for days or weeks at a time, warming up to normal body temperatures for a few hours or days. The Woodchuck's heart rate drops 95% (from 80 to 4 beats per minute). Its temperature plunges from 98° to 40° to 57°.

BATS are also true hibernators. They clump together, using each other's bodies to keep them from getting cold in hollow trees and on damp walls of caves, mines and cellars.

(2) The deep sleeper's heart rate, temperature and respiration drop only slightly and they occasionally waken for brief periods of time during the winter for a day or so every 2 - 14 days.

BEARS sleep in dens and get their energy by burning their stored fat. They also breathe less often, the heart beats slower, and the body temperature drops nine degrees below normal. The metabolic rate is reduced by only 50%, so they can awaken quickly. Bears do not eat or drink, pass no body wastes and keep their proper body water balance as a true hibernator does.

Mammals weighing 2 - 11 pounds do not waken during their winter sleep. It exerts too much energy during the long awakening time.

What regulates this predictable event, no matter what the lighting or temperature may be has interested scientists. Scientists could not locate the internal clock that controls hibernation schedules. Norman F. Ruby and his colleagues (Stanford) report ". . . the brain's hypothamlamic suprachiasmatic nucleus (SCN) -- best known for its role in governing the body's daily rhythms also regulates hibernation". (Science News). Because of this researchers found that Marmots and male Belding Ground Squirrels will emerge through the snow because their internal clock says "it is time". The 10 lb. Marmot has cushions of fat to live on until they can find food. The female Belding Squirrel will check out the temperature of the soil plug. If it is warm enough, she will emerge.

POOR-WILL is the only bird that hibernates. It tucks itself into a rocky crack or rotting log. You cannot see it breathing or feel its heartbeat when it sinks so deeply into torpor.

INSECTS Most adults die in the fall. Only the eggs and young surviving. The insects that winter over are in a state of suspended animation called "diapause", a super hibernation with the insect's metabolism being so low it is only minimally alive. The only adult insect that hibernates is the bald-faced hornet queen. She hibernates by crawling into or under a big, rotting log, using the snow as a blanket.

Other insects fill their abdomen with "antifreeze" - alcohol glycerol. The Eastern Tent Caterpillar contains 35% glycerol by body weight and prevents ice crystals from forming in its body fluids. Frogs and toads also contain glycerol so they can hibernate under a shallow covering of leaf litter in subfreezing temperatures.

WAKE-UP CALL: Warming up from deep hibernation is called arousal. To begin this process, deep hibernators use a kind of body fat as fuel. This fuel heats up the heart and blood. The warm blood is pumped to the brain and the rest of the body. The shivering begins, which makes their muscles move and the rest of their body soon follows. A small bat’s arousal time is up to ½ hour; a marmot takes many hours. The study of hibernation has resulted in low temperature surgery that saves lives.

References:

Coping with the Cold, George H. Harrison, National Wildlife, Feb/Mar, 1988

Birder's World 1996 Calendar

Feel Like Hibernating? Blame the Brain. T. Adler, Science News, 9/7/96 Vol. 150, No. 10, Pg. 48

Were Do Ants Go in the Winter?, National Geographic World, 9/93, Pg. 31

Hibernation, Linda Nietfeld, Ranger Rick, 12/92, P12-14

Our Hibernating Mammals, Frank Knight, Conservationist, 4/93

The Encyclopedia of Animal Behavior, Prof. Peter J.B. Slater, Rhythms of Behavior, Pg. 45

The Cold Truth About Ice, Richard Wolkamier, National Wildlife 12/11/84, Pgs. 11-12

"Do Lions Purr? And Why Are There No Green Animals?" Doug Stewart, National Wildlife, Aug./Sept. 1995, Pg. 37

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