As a close relative of bears, why don’t giant pandas hibernate?

Key Points

★ Giant pandas are able to lower their metabolic levels to cope with the cold winter, but they do not have the habit of hibernation.

★ Eating a lot and consuming little is the magic weapon for giant pandas to survive the cold winter.

The national treasure giant panda is adorable and loved by many people. Whether it is at the panda research base or zoos in various places, wherever they are, there is no shortage of fans to worship and watch. As the weather gets colder, many people have discovered a problem: it is said that giant pandas are relatives of bears, but bears hibernate in winter, so why do our giant pandas still eat, play, and be cute as usual?

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01

Hibernation is a habit of "small animals"

First of all, I need to explain one thing: not all bears hibernate. In order to adapt to the cold weather, giant pandas have the ability to slow down their metabolism, but they do not have the habit of hibernating.

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In order to cope with the harsh natural environment and reduce energy consumption, some warm-blooded animals such as hedgehogs and marmots relax the regulation of body temperature and reduce their body temperature, metabolic rate, heart rate, etc. to very low physiological levels, entering a state of sleep for several months, which is hibernation. Some animals also enter a state of sleep in response to the summer heat, which is called aestivation. Some animals such as bats and hummingbirds enter a state of sleep in all seasons due to lack of energy. This phenomenon is called day hibernation.

Generally, hibernating animals are relatively small, and large animals rarely hibernate to survive seasons of food shortage.

02

Hibernation of large carnivores is actually "winter sleep"

Hibernation of large carnivores such as bears is an interesting phenomenon. For example, when black bears hibernate, they do not eat, drink, urinate or defecate. Although their body temperature drops, it does not drop much, to about 32-33°C. They can wake up at any time when disturbed. What is even more interesting is that bears also raise their offspring during hibernation. Some scholars believe that this phenomenon of bears is a winter sleep phenomenon of carnivores, not true hibernation.

According to research, the giant panda has appeared 8 million years ago. Under the pressure of the last ice age of the Quaternary period about 10,000 years ago, most members of the "giant panda-saber-toothed elephant fauna" that once flourished at the same time as it have become extinct, so the giant panda is also known as a "living fossil."

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The giant panda belongs to the Ursidae family of the order Carnivora in systematic classification, but its diet is highly specialized to eating bamboo. From the anatomical characteristics, the giant panda's digestive tract is still basically the morphological structure of a carnivore, but in order to adapt to the habit of eating bamboo, some corresponding changes have also occurred, especially changes in intestinal microorganisms, which can help them digest and decompose cellulose. However, the overall structure of the digestive tract is similar to that of carnivores or omnivores, such as a relatively short intestine, a simple structure, and no cecum.

03

Eating a lot and having a low metabolism help giant pandas survive the winter

The digestive physiology of giant pandas is also very special: although their staple food is bamboo, due to the structure and function of the digestive tract, the efficiency of bamboo utilization is very low. It is reported that the digestion efficiency of giant pandas is only 17%. At the same time, the residence time of food in the digestive tract is relatively short, only about 8-9 hours, so the giant pandas eat a lot every day. According to relevant research, a giant panda will eat about 10-20 kilograms of bamboo every day.

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Eating large amounts of food, passing it through the digestive tract quickly, and relying on the help of intestinal microorganisms are strategies for giant pandas to obtain energy and nutrition. At the same time, giant pandas have the ability to maintain a low metabolic level, so that they need less energy to maintain their own survival and daily activities. The activity level of giant pandas in the wild is very low, and we can also see this feature in zoos. Giant pandas always move slowly, and their lazy appearance also increases their cuteness. In terms of morphology, some energy-consuming organs of giant pandas, such as the brain, liver, and kidneys, also tend to shrink.

The giant pandas need to eat constantly, and their energy demand and consumption are relatively low. These long-evolved survival strategies determine that they can safely survive the winter without hibernation.

Author: Wang Dehua, Researcher, Institute of Zoology, Chinese Academy of Sciences

Review | Huang Chengming, Researcher, Institute of Zoology, Chinese Academy of Sciences

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