Resource Ramblings 2005-11


It is the time of year that each of us begin to prepare our homes, cars, and other belongings for the winter ahead. We do this by such things as changing antifreeze in radiators, getting out snow or studded tires, checking insulation in attics, and putting up storm doors or windows. Some people even store additional food so trips to the store will be less and eat a bit extra to add an insulating layer to offset those winter temperatures. All these actions help to make life more pleasant during the long winter ahead. It is interesting to note that nature also prepares for winter.

The first example comes from birds. Most of us are aware that many bird species migrate. Birds migrate for a variety of reasons, but the most important reason is to find a source of unfrozen food. Some species will fly only short distances, while others thousands of miles. Most of us equate this to an inbuilt desire to stay warm, which is important, but food is the source of energy that sustains life.

Pine Siskin - Carduelis pinus
Pine Siskin - Carduelis pinus

NPS Photo

Birds that do not migrate have developed physical and behavioral adaptations that help them find adequate food resources and survive cold temperatures. Birds that may be seen in this area during the winter are: Dark-Eyed Junco, Black Capped Chickadee, Pine Siskin, Downy Woodpecker, Hairy Woodpecker, Pine Grosbeak, American Goldfinch and birds of prey.

Behavioral adaptations of many birds include finding or constructing warm sleeping quarters; eating lots of food during to day to store plenty of fat; storing food in “caches”; and may birds simple snuggle with other birds to keep warm.

Physical adaptations are things such as adding additional feathers to the body to stay warm; “fluffing” feathers for added insulation; shivering to help maintain body temperature; and some birds even go into torpor.

Torpor is a physical condition in which an animal reduces physical activity (some for hours and others for days) and may reduce heart rate, respiration, and lower the body temperature slightly to use less energy. However these animals can be easily disturbed. Examples of animals that go into torpor include badgers, raccoons, skunks, bears, chipmunks, ground squirrels, rattlesnakes and other reptiles.

Hibernation, like torpor, is an adaptation that allows some animals to conserve energy and survive periods when food is hard to find. During hibernation an animal’s heart rate, breathing and metabolism slow down so much that they can survive the winter with very little food. Even an animal’s brain will cease normal activity.

For some species, reducing the food supply, changing the temperature, or reducing the amount of light can induce hibernation. Other animals seem to have an internal clock that tells the animal it is time to go to sleep.


Many bats spend the last days of the summer feeding to build fat reserves for winter hibernation. In the fall, hibernating bats congregate in large caves with low temperatures and high humidity. Bats will hibernate in individual locations or tightly packed clusters of hundreds to thousands of bats. Individual bats may wake up and spend time flying around the cave before resuming their hibernation. Bats are sensitive to noise and light and can be easily aroused from hibernation by careless cavers. Each time they are awakened, precious energy reserves (fat) are depleted, and with too many disturbances they will not survive until spring.

The fat that animals store to survive the winter plays two roles. It insulates animals to help keep them warm and provides energy while animals are not eating. Examples of animals that hibernate include grizzly bears, bats, prairie dogs (except black-tailed prairie dogs), groundhogs, and woodchucks.

Some extreme amphibians and insects winterize in a completely dormant state in which they have almost no bodily functions and can be divided into two groups: species that can tolerate up to 65 percent of their body water freezing and species that produce compounds that keep their body fluid from freezing far below 0° Fahrenheit.

Wood Frog
Wood Frog

NPS Photo

Wood frogs are a good example of species that can have partially frozen body water. As the temperature drops, these frogs produce an antifreeze, which allows them to control where and when ice forms. With this control, wood frogs can ensure that ice does not form within their cells, which would kill them, and they can ready their metabolism to stopped. Once frozen, a wood frog does not breathe or bleed, and has a barely recordable heart beat. When temperatures climb, all functions return.

Gall moth caterpillars are in with the second group and avoid freezing at all costs. If water is free from impurities it can remain liquid down to temperatures of -40° Fahrenheit. These caterpillars can empty their guts of food particles and bacteria and produce an antifreeze that lowers the temperature at which ice forms. These two adaptations allow gall moths caterpillars to survive temperatures as low as -36° Fahrenheit.

These adaptations have provided winter protection to a variety of species. As such, they are equipped to survive in their environment. We must be careful in our actions to not place undo their winterization so these fittest may survive.

Comments and feedback about Resource Ramblings are encouraged and can be made to Dan Foster, in person, or via email.

Last updated: April 10, 2015

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