Hibernation is Just the Tip of the Iceberg

Guest Opinion

As temperatures drop and days and nights become colder, wildlife must adapt quickly to survive. Hibernation helps bears sustain themselves through a long winter, but how does other wildlife survive these extreme conditions?

What does wildlife do to withstand such grueling cold?

When food becomes scarce and caloric needs increase, we are familiar with the bears’ hibernation strategy. However, when temperatures suddenly drop at any time of the year, without a season of preparation through eating berries and other foods, some mammals can enter another physiological state called torpor.

Torpor vs. hibernation

Torpor can occur at any time of the year, lasting for short or prolonged periods in response to a sudden drop in temperature and the increased caloric demands of maintaining body heat. Hibernation, by comparison, is a winter process preceded by months of feeding in preparation for the long period of dormancy. (There are also two types of hibernation — facultative and obligate — but those distinctions are not essential to this discussion.)

Further, torpor can look a lot like hypothermia. However, it is the combination of reduced body temperature and a reduced metabolic rate that identifies the condition as torpor rather than hypothermia.

Reptilian brumation

The alligator has an amazing adaptation, making it one of the more cold-tolerant reptiles. It can survive beneath frozen ice and tolerate temperatures as low as 40 degrees below zero. It must poke its nose through the ice to breathe, but otherwise remains in this dormant state. Here is an alligator at North Carolina’s Shallotte River Swamp Park.

Brumation in reptiles differs from hibernation in mammals. Alligators in brumation enter a state of suspended animation, but they experience periods of activity and continue to drink water to avoid dehydration, although they do not eat. Hibernation, by comparison, involves a much deeper state of dormancy.

Then there is a bird’s regional heterothermy

Ducks, geese and gulls can stand on ice for long periods because they are able to keep their core body temperatures warm while their feet remain nearly frozen. They accomplish this through a physiological process called regional heterothermy.

This process allows birds to conserve heat in their core without expending additional energy to warm their feet. The heat-exchange system is designed with veins surrounding arteries in the feet. Blood returning from the feet is warmed through this exchange, conserving most of the body’s heat for the core.

The legs of birds consist primarily of bones and tendons rather than the muscles and nerves that require more energy to keep warm.

This begs for a diagram, so here is a graphic description of how this process works (from Khan Academy):

What does adaptation mean for invasive species?

Whether an invasive species arrives in a new habitat on its own or is released or introduced by humans, it may not have the adaptations needed to survive extreme weather events such as a polar vortex.

In Florida, during a period of extreme cold, spectacled caimans (an invasive crocodilian species) disappeared completely following the 2010 freeze because they could not adapt to the cold, while native alligators survived.

Native species that do not adapt well

The manatee is notoriously poor at adapting to cold weather and can die if water temperatures drop below 68 degrees. Despite its appearance, it actually has very little insulating fat to keep it warm. When exposed to cold temperatures, its physiological response appears to trigger a weakened immune system, causing it to become ill quickly. This entire process is well documented and is called manatee cold stress syndrome.

The opossum is another species that does not adapt well to the extreme cold associated with polar vortex conditions. While opossums can survive normal cold winters, their hairless tails and ears make them vulnerable to frostbite. Following extreme cold periods, such as a polar vortex, opossums may be seen with missing tails or ears that appear tattered from frostbite injuries.

Animals in captivity

Most states and local governments have ordinances and laws requiring animals to have adequate shelter during extreme weather events. In Texas, for example, the care of dogs requires shelter and humane tethering practices during extreme weather, which is defined as:

“Inclement weather” includes rain, hail, sleet, snow, high winds, extreme low temperatures, or extreme high temperatures.

Livestock care during extreme cold is regulated by individual states, where failure to provide adequate care may constitute animal cruelty. There is no federal law specifically regulating the care of cattle during cold weather, but the U.S. Department of Agriculture (USDA) does provide recommendations.

Calves are particularly vulnerable. Their legs are susceptible to freezing, and severe injuries may require euthanasia. Providing shelter and plenty of roughage, such as hay, is recommended to help livestock withstand cold weather.

Most livestock owners want nothing more than to protect their animals, but doing so also means being prepared for extreme cold events. In Texas in 2016, 15,000 dairy cows froze to death during a snowstorm. During the Great Texas Freeze of 2021, livestock losses reached $228 million.

Wildlife have developed adaptations to withstand extreme cold, whereas domesticated animals have been displaced from their original habitats and, unfortunately, must rely on humans to ensure their safety.

What does this mean for humans facing extreme weather?

Looking ahead, researchers are considering how humans might benefit from these same mammalian processes. Medical research has observed that mammals capable of entering a state of torpor may have an advantage over humans, who are homeotherms. Their tissues appear better able to avoid potentially damaging organs during medical emergencies such as a stroke or cardiac arrest.

The potential use of torpor in space travel is another area of research. Inducing a torpor-like state could make journeys possible that might otherwise exceed the normal human life span.

Final thoughts

Winter will take its toll on older, infirm and sick wildlife, but over time, these incredible physiological responses to survive the cold have proven remarkably effective.

During the Great Texas Freeze of 2021, fish along the coast were devastated by the cold and have taken years to recover. Texas Parks and Wildlife (TPWD) reported that 3.8 million fish representing 60 species succumbed to the cold along the Texas coast. Sea turtles were also “cold stunned” and unable to navigate to warmer waters, requiring extensive rescue efforts to try to save them.

Yet, remarkably, wildlife has developed physiological responses to extreme weather events that are unique to each animal classification and habitat. Domesticated animals make humans morally, and sometimes legally, responsible for protecting them from extreme cold.

These physiological mechanisms for withstanding extreme weather events may even inform the future survival of humans, whether on Earth, during space travel or on otherwise uninhabitable planets.

To read more articles by Professor Sutton go to:  https://profvictoria.substack.com/ 

Professor Victoria Sutton (Lumbee) is a law professor on the faculty of Texas Tech University. In 2005, Sutton became a founding member of the National Congress of American Indians, Policy Advisory Board to the NCAI Policy Center, positioning the Native American community to act and lead on policy issues affecting Indigenous communities in the United States.