Dormice that Spend Half their Life Sleeping

Speaking of the best sleepers, many people will immediately think of sloths that hang on trees and sleep soundly all day long.

The Rapper sloth is a really model of “contrast cute”. Image source: Rio 2

However, the sleeping ability of sloth isn't necessarily as good as that of another sleepy animal: the dormouse. How sleepy are dormice? Let's put it this way, they can starve to death in their sleep, and this is veritably “sleeping with life”.

African dormice. Image source: Carleton

Today, let's learn about this little animal that sleeps half its life.

In the Name of Sleeping

The dormouse is actually not an animal, but a generic term of many animals, such as Rodentia, Sciuromorpha and Gliridae. The most common species are Muscardinus avellanarius in Muscardinus, Dryomys nitedula in Dryomys and Eliomys quercinus in Eliomys, etc. Dormice are small in size, and measure only 6-19 cm in length and weigh 15-180 grams even in adulthood. They somewhat resemble mice.  

Dryomys nitedula. Image source: gbif

The most striking feature of dormice is that they are especially good at sleeping and able to sleep for six months at a time. There are many animals that can hibernate (or aestivate), but it is rare to find animals that can sleep for half a year at one go as dormice do. They are called dormice perhaps because they're too good at sleeping.

Garden dormouse, Image source: gbif

Don't assume that dormice are as sluggish as similarly somnolent sloths, just because they sleep for a long time. In fact, dormice are pretty agile creatures. They mostly perch on trees, climb very well and move nimbly. 

Muscardinus avellanarius. Image source: Wildlife Trusts

Dormice often move and forage at dusk and dawn, when the light is dim. For this reason, they develop a keen sense of hearing and often make different sounds to exchange information. Dormice are omnivores and able eat a wide variety of food, such as plant fruits, flowers, insects and other small invertebrates. Therein, nuts high in protein and fat are their favorites. Compared with other rodents, dormice lack cecum in digestive tracts (where other rodents digest plant cellulose), so they have a poor digestion ability for foods rich in cellulose.

With long sleeping hours, dormice have to concentrate their annual tasks, for example, feeding offspring, within less than half a year. As a rule, when they wake up from hibernation for the first time, the baby dormice's childhood has already ended (i.e., reach sexual maturity). They wake up sometime between spring and summer, and the weather is very warm. Naturally the first thing to do when they wake up is to search for food and fill their stomachs, and hurry up to complete the important task of reproducing offspring.

Generally, dormice breed once a year (or twice occasionally) and give birth to 3-4 cubs at a time. Before living on their own, the cubs need to be taken care of by their mothers for 6-8 weeks before they can fend for themselves. When the cubs are almost able to find food to feed themselves, autumn is approaching and dormice have to prepare for the upcoming hibernation.

A Muscardinus avellanarius taking care of its cub. Image source: Wikipedia

How Good Dormice Are at Sleeping 

How good dormice are at sleeping? Usually, in October, when the weather is not too cold, they begin to prepare for the long hibernation in succession. They won't wake up until next May, when the weather is quite warm. During the hibernation, the metabolism and heart rate of dormice bottom out-to the extent of barely sustaining life. Only in this way can they maximize the energy stored in the body and survive the long hibernation.  

A dormouse in hibernation. Image source: Wikipedia

During the hibernation, dormice occasionally wake up briefly and supplest energy by eating some food stored nearby. But they don't truly wake up until the weather thoroughly warm. Sometimes the temperature rises slowly, and some dormice even starve to death during sleep, because they fail to wake up in time.

It seems a little too late to end hibernation in May, but actually only at this temperature can dormice obtain enough food. If they wake up too early, they may find it difficult to survive because of the increased metabolism and inadequate food that is available. 

Dormice in hibernation. Image source: ptes

It should be noted that dormice (like other hibernating animals) are particularly vulnerable when they just wake up from hibernation. Their energy reserve has been depleted, but their energy consumption has returned to normal, so they have to forage and replenish energy. Normally, hibernating animals determine the best time (often a time when they can get enough food) to wake up according to weather changes. In recent years, the increasingly erratic temperature fluctuations have exerted a great impact on hibernating animals around the world. Sometimes, warm winters can make hibernating animals wake up early when there is not enough food, making their survival difficult.

For dormice, long hibernation time is merely a manifestation of their ability to sleep. Even if they're not in hibernation, they are very adept at sleeping. In summer, dormice begin to move at dusk, and go back to sleep in their nest in the bush during the day. This sleep does not require the same metabolic reduction as hibernation, but it is also a heavy sleep and may take dormice several minutes to wake up once disturbed.  

Let's put it this way, dormice generally live for more than 5 years, of which about 3.75 years are spent on sleep. I wonder whether “corporate slaves”, who complain about shot age of sleep every day, would feel jealous.

Maybe Sleeping is the Way They Survive

Having seen dormice sleep every day, you might think they have no survival competitiveness at all, but the reality is that they're actually quite successful at adapting to their environment. 

At present, dormice have 9 genera and 28 species, which are distributed in Europe (north to southern Scandinavia), Asia (east to southern China and Japan), Africa (south to sub-Saharan Africa) and can acclimatize themselves to temperate, subtropical and tropical climates. Most dormouse populations are not so small that they carry little risk of extinction. However, some species are on the IUCN Red List of Threatened Species and need protection. 

In short, dormice's long sleep is very energy-efficient, which enable them to survive with less energy. During dormancy, they don't have to need around for food, but find a safe place and lie down. This partly reduces the competition between dormice and other animals.

Perhaps the way dormice survive is to “lie down”, wake up to eat and sleep when they are stuffed. 

References:

[1] Gakken Holdings Co., Ltd. Animals: [M]. Zhengzhou: Henan Science and Technology Press, 2004.