In the colder months, many animals hibernate to escape the harsh weather conditions. While hibernation is an effective way to conserve energy, it can also be dangerous.
What is Hibernation?
Hibernation is a state of inactivity and metabolic depression typical of mammals and birds. Hibernation usually occurs during winter, but animals may also hibernate at other times of the year.
Why do animals hibernate?
The main reason animals hibernate is to conserve energy during periods when food is scarce. By sleeping through the winter, animals can avoid using up precious resources searching for food that isn’t there.
How does hibernation work?
Hibernation is triggered by a decrease in temperature and an increase in day length. These signals tell the animal’s body to start stockpiling energy in the form of fat.
As the animal’s body fat stores increase, its metabolism slows down. The animal’s heart rate and breathing rate also decrease, and its body temperature drops. In some cases, such as with ground squirrels, an animal’s body temperature can drop so low that it becomes indistinguishable from the surrounding air.
Once an animal’s body has reached its lowest temperature, it can enter a state of torpor. Torpor is a state of reduced physiological activity, characterized by a drastic decrease in metabolism and heart rate. Animals in torpor appear to be asleep, but they can be awakened fairly easily.
List of Animals that Hibernate
Bats are the only mammals that can truly fly, and they come in all shapes and sizes. Some bats eat insects, while others feast on fruit. All bats, however, share one thing in common: they hibernate.
Like other hibernating animals, bats slow their metabolism down to a crawl during hibernation. Their heart rate and body temperature drop, and they may even enter a state of torpor.
Bats usually hibernate in caves or other protected areas. In some cases, however, bats will hibernate in trees, under bridges, or even inside houses.
One reason why bats may choose to hibernate in these unusual places is because they are trying to avoid predators. Another reason is that these locations tend to have a stable temperature, which helps the bats conserve energy.
Bumblebees are large, hairy bees and are close relatives of the well-known honeybee. Most species of bumblebee live in colonies, but their colonies are much smaller than the honey bees or wasps who can have up to several thousand individuals, the bumblebee colony will only consist of around 50 – 150 individuals.
Their fat body is a nutritional store. Before hibernation, queens eat as much as they can to enlarge their fat body. The fat in the cells is used up during hibernation.
Bumblebees keep a body temperature of 34 to 38 degrees centigrade, this is why it is common to see bumblebees even on colder and rainy days in the spring and summer. Only in winter, when temperatures drop, they will go into hibernation. Just like social wasps, the bumblebee colony will die off at the end of summer. The new queens will then find somewhere to hibernate during the winter, usually underground and emerge to find new nesting ground ready to start a new colony in spring.
Chipmunks are small rodents of the squirrel family with a total of 25 different species (see bottom of page), all part of the scientific family, in the family Sciuridae. There are three genera in this family: Tamias (eastern North America), Neotamias (western North America) and Eutamias (Eurasia).
Chipmunks are lively little creatures that are found mostly in North and West America with one species (Asia’s Tamias sibiricus) native to Eurasia. Chipmunks are kept as popular and entertaining pets.
Chipmunks are solitary animals and male and female do not pair until breeding season. Although chipmunks hibernate from late autumn until early spring, they do not store fat, instead they slowly gnaw away at their supplies throughout the winter, waking every 2 weeks or so to eat.
Common frogs are largely terrestrial outside the breeding season and can be found in meadows, gardens and woodland. Common frogs hibernate and breed in puddles, ponds, lakes and canals, muddy burrows and can also hibernate in layers of decaying leaves and mud at the bottom of ponds. The fact that they can breathe through their skins allows them to stay underwater for much longer periods of time when they are hibernating.
Common frogs are active almost all of the year, only hibernating when it gets very cold and the water and earth are frozen. In the British Isles, common frogs typically hibernate from late October to January. They will re-emerge as early as February if conditions are suitable and migrate to bodies of water such as garden ponds. Common frogs hibernate in running waters, muddy burrows and can hibernate in layers of decaying leaves and mud at the bottom of ponds. The fact that they can breathe through their skin allows them to stay underwater for much longer periods of time when they are hibernating.
Grizzly bears (Ursus arctos horribilis) are brown bears found in North America, in areas such as Alaska and Canada. They are huge in size, weighing up to 36kg. Contrary to popular belief, they are just one of a number of subspecies of the brown bear, and can easily be differentiated from black bears.
Grizzly bears have a large range and need lots of space to live. They are omnivores and both an apex predator and keystone predator. They also hibernate in the winter months.
Fortunately, these bears are listed as “least concern” on the IUCN Red List, and are not yet in danger of becoming endangered. There are currently about 60,000 wild grizzly bears located throughout North America.
Grizzly bears hibernate at the beginning of winter, usually around late November, but the date depends on the temperature, food supply, and snowfall. In places where the climate is warm, such as California, bears do not hibernate. The main reason for hibernation is the cold weather and lack of food during this time.
They hibernate in dens, which are usually located on north-facing slopes an altitude of about 1,800 meters (5,900 feet). Before they hibernate, grizzly bears go through a period of hyperphagia or polyphagia (extreme sensation of hunger or strong desire for eating), and consume a large amount of food. During this time they can gain up to 180 kg (400 lbs)! Pregnant females are the first to enter dens, followed by females with cubs, and solitary males enter dens last.
While hibernating, grizzly bears do not eat or even go to the bathroom. They enter a deep sleep, and their heart beat slows from 40 beats per minute to only 8 beats per minute. However, their hibernation is not as deep of a sleep as some other hibernators, like bats or ground squirrels, and they will quickly wake up when disturbed.
Pregnant females give birth in the dens and nurse their cubs until they are large enough to venture outside in the spring. Male grizzlies wake up from hibernation in mid-March, while females and grizzly cubs are the last to leave the den, in about April or May.
Groundhogs enter into true hibernation and are one of the few species to do so. They will often build a separate “winter burrow” for this purpose. They hibernate from October to early spring, around March or April, in most areas, although in warmer areas will hibernate as little as three months. Some fellow hibernators, such as rabbits, opossums, raccoons and skunks, will move in with groundhogs for the winter, hibernating in one of the rooms in their burrow network.
When they enter into hibernation, their body temperature drops to as low as 35 degrees Fahrenheit, their heart rate falls to 4–10 beats per minute and their breathing rate falls to one breath every six minutes. Males emerge from hibernation before females.
Hedgehogs have changed little over the last 15 million years. Like many of the first mammals they have adapted to a nocturnal way of life.
The male Hedgehog is called a ‘Boar’ and is slightly larger than a female Hedgehog which is called a ‘Sow’.
Hedgehogs hibernate alone from November to April under a supporting structure such as a shed, wood piles, brambles, open compost bags or bonfire heaps. They may, however, emerge to forage at night during warm winter spells. In summer, hedgehogs shelter during the day in temporary nests of leaves, moss and grass. By autumn, hedgehogs have dramatically put on weight in preparation for their hibernation. They hibernate until the following March or April, during which time their body temperature and heart beat fall dramatically, from 190 to about 20 beats per minute. Most hedgehog deaths occur during this hibernation period.
The slow worm (Anguis fragilis), also known as a deaf adder, a blindworm, or regionally, a long-cripple, is a reptile native to western Eurasia. Its genus is Anguis. Despite its name and appearance, it is not actually a worm or a snake, but a lizard, belonging to the family Anguidae and the order Squamata. They have been shown to be a species complex, consisting of 5 distinct but similar species.
The slow worm is a semifossorial (burrowing), legless lizard, which spends much of its time hiding underneath objects. Like many other lizards, they autotomize, meaning that they have the ability to shed their tails to escape predators, the most common of which is the domestic cat. The ability to shed their tail is also where they get their scientific name ‘fragilis’ (fragile).
This species hibernates spend the colder months from October to March underground, only emerging in April to breed. They may disappear underground again during the hottest part of the summer. They are not normally territorial, but fights between males can occur during the breeding season.
Skunks can be found solely in the New World, across North America and South America. The different genus can be found in different areas. They inhabit woodlands, deserts, grasslands, and rocky montane areas, but do not occur in dense forest. These animals are mainly omnivorous, eating vegetation, insects and other small invertebrates, and smaller vertebrates.
Skunks go into their dens for extended periods of time in winter. During this time, they remain generally inactive and feed rarely, going through a dormant stage. Over winter, multiple females (as many as 12) huddle together.
The cottonmouth snake is a large snake that can measure between 32 and 42 inches in length, making it the largest of the genus Agkistrodon that is belongs to. Their bodies are thick and muscular, weighing between 201.1g and 579.6g, with males being heavier than females.
These snakes have keeled or ridged scales and are gray, tan or dark olive-brown to almost black with 10–17 dark brown to almost black dark crossbands that may not be visible. They may also have dark spots and speckles, although the pattern darkens with age so adults may become uniformly black. Their underside is tan or gray with dark blotches. It is pit viper which means it is a venomous snake.
Cottonmouths may hibernate over winter in the colder, northern parts of the US. They spend hibernation in burrows made by other animals, including crayfish and tortoises, or under some other form of cover.