Hibernating black bear with cub

Hibernating black bear with cub (via)


We commonly picture bears, bees, and groundhogs hibernating during the winter, but did you know that some creatures retreat from the world in the summer? These heat-adverse animals estivate.

Warm-blooded animals, whose body temperatures are self-regulated by their internal organs, use external temperatures and food as their bio-fuel. But when external temperatures are very cold and food sources are scarce, as in the winter, some warm-blooded animals survive by becoming inactive, slowing down all of their physiological activities, and sleeping as far away from the cold as they can. Some snakes, alligators, and other cold-blooded animals have their own version of hibernation at times when the weather gets too cold for them.


British dormouse

British dormouse hibernates for 6 to 7 months during cold weather and takes only 10 minutes to fully awake. (via)


But another escape from the weather is undertaken by some cold-blooded animals in hot weather. This is called estivation (or aestivation), and it takes place primarily in hot, dry climates, by animals that cannot survive that weather, due not only to the heat, but to food shortages.


Spotted Turtle

Spotted turtle  Turtles hibernate in cold weather and estivate in very hot weather! (via)


Torpor describes the state of an animal's physiology when it is hibernating or estivating. It is characterized by a slow-down of all physical and chemical actions in the body.  When an animal is coming out of torpor back into its non-torpor state, the change may take place slowly, as when bumble bees first come out of torpor and you see them lying totally still on the ground in spring. They are just waking up slowly. Other creatures, like bears, tend to come out of torpor quickly.

"Torpor" may also be used to describe a short period of time when an animal shuts down in order to restore equilibrium, as when a hummingbird takes a night time rest to restore needed energy.


Hummingbird in torpor

Hummingbird in torpor upside-down. (via)


Not all animals that hibernate do so all winter and not all animals who estivate do so all summer. Brown and black bears are known to hibernate pretty much all winter. The Fat-tailed dwarf lemur (Cheirogaleus medius), which stores food in his tail, hibernates for seven months. This lemur cannot self-regulate his body temperature, so he has to find a well-protected hide-away.


Cheirogaleus medius

Fat-tailed dwarf lemur (Cheirogaleus medius) Photo: Petra Lahann


Some hibernating animals come out of their hiding places after a few weeks to get fresh air, to defecate, urinate, and to hunt for whatever food they can find. They may go back to hibernation for another few weeks, or may not.  Estivation tends to be more short-term than hibernation, but both physiological states vary by species and climate conditions.


Here is some engaging information about specific animals that hibernate and estivate:


Hibernating Animals

1. Bears: Brown and black bears hibernate for several months during the winter; female bears are known to give birth to cubs and nurse them while hibernating. (See lead photo.) Female polar bears may also hibernate in winter to give birth to their cubs.

2. Fat-tailed dwarf lemur: Not only is this lemur the only cold-blooded mammal that hibernates the longest of any mammal, but he is the only known animal to experience REM sleep during hibernation, which means he can dream! (via) Some experts say this animal hibernates; others say it estivates (see above photo).

3. Common poorwill: Hailing from British Columbia and southeastern Alberta, Canada, this is the only bird known to hibernate in winter, as most birds migrate in cold weather. Nevertheless, the Common poorwill does get as far as southern California and the border of New Mexico before it goes into short periods of hibernation.


Common poorwill

Common poorwill: photo by Connor Long via Wikipedia


4. Bumble Bees: Talk about a matriarchal community! While honeybees work all winter long, queen bumble bees mate and burrow in the winter, leaving their mates and all worker bees to die in the cold. The newborn bees then become the worker bees for the following warmer seasons. (via)

5. Groundhogs: These spring-predicting members of the squirrel family are true hibernators, burrowing in October and not coming out until Spring. When you think about a hibernating animal slowing down its physiological activity, think about the groundhog whose temperature drops from 99°F to 40°F, and whose heartbeat slows from 80 beats per minute to 5 beats per minute during hibernation. Imagine that! (via)



"I think I'd better go back to bed!" image


Estivating Animals

1. Desert tortoises: There are two species of desert tortoises in the southwestern U.S. One is called Agassiz's and the other Morafka's, both named for the scientists that identified them. Their lifespan, if undisturbed, can be from 50 to 80 years, but they spend 90 percent of their lives underground where they estivate during hot temperatures and hibernate in cold weather. Desert tortoises tend to share their burrows with other tortoises, as well as certain snakes, squirrels, quail, and even burrowing owls. (via)


Dessert tortoise (Agassiz's)

Agassiz's Desert tortoise (photo)


2. Gastropods: Commonly known as snails and slugs, gastropods can be found in hot, dry climates or in cold ones, on water, or on land. The major difference between a snail and a slug is that snails have shells large enough to fully hide within them. During estivation a snail will hide in its shell and form a layer of mucous which can protect him and keep him alive for up to three years!

3. California Red-Legged Frog: This species of frog which is native to southern California and Baja, Mexico, can also be found in "pools of slow-moving streams, perennial or ephemeral ponds, and upland sheltering habitat such as rocks, small mammal burrows, logs, densely vegetated areas, and even, man-made structures."  Whether eaten by man or beast, the frog that was made famous in Mark Twain's The Celebrated Jumping Frog of Calaveras County is now a threatened species. (via)


California red-legged frog

California Red-Legged Frog (photo)


4. Lizards: Lizards live in hot climates. To regulate their body heat, they must live in a perfect range of external heat. But when it gets too hot or too cold, as it does in the deserts where they live, they go into estivation, burrowing in the dirt, sometimes with their "nostrils and eyes above the dirt." (viaGila monsters and geckos can store water and nutrients in their fatty tails for these times of dormancy. (via)

5. Lungfish: There are only six species left of the ancient lungfish and they live in the warm fresh waters of Africa, South America, and Australia. Lungfish are the only fish known to breath from their lungs, although the Australian lungfish also breathes through its gills. When their habitats get hot and dry, lungfish estivate in moist water beds and secrete a mucous coating that keeps them from dehydration. They can remain in this state for up to four years, if necessary. These are long-lived fish. There was a Queensland lungfish in a Chicago aquarium that was at least 84 years old when it was euthanized due to poor health! (via)


Queensland Lungfish

Queensland Lungfish (via)


Just like humans, animals, fish, birds, and even insects instinctively know how to adjust their physiological responses to their environments and their activities. Like the hummingbird who can beat its wings up to 80 times per minute with a heartbeat of over 1,000 beats per minute, we all need some kind of rest or "torpor." (By the way, in torpor a hummer's heartbeat can drop as low as 50 - 180 beats per minute! via)


Sources: I have used many sources to prepare this information. Rather than list them all at the end, you will find them linked within the content of the blog.


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