Hibernation vs. Torpor: What's The Difference? 

Many factors in the wild are responsible for several animal behaviors. Some animals can’t handle cold temperatures, so they become dormant until the weather warms. Other animals enter a state of inactivity to wait out a period of food scarcity. Keep reading as we examine the differences between two primary dormancies in animals: hibernation vs. torpor. 

We will discuss the definitions of torpor and hibernation and what happens during an animal’s sleep. We will explore four differences between hibernation and torpor, other types of dormancy, and examples of torpid and hibernating animals. 

Table of contents:

What is torpor?

Torpor is a method various animal species use to conserve energy. An animal enters a torpor state as a survival tactic to save energy during the winter period. It is similar to hibernation, but it is not true hibernation. 

Unlike hibernation, torpor is an involuntary state an animal enters as the environmental conditions change. In torpor, animals lower their body temperature, metabolic rate, heart rate, and breathing rate. It is a lighter state of hibernation that lasts for a short period³, sometimes a few hours.

Many animals experience daily torpor based on their feeding pattern. Nocturnal animals experience torpor in daylight, while day animals’ torpor state occurs at night. They maintain their normal body temperature and basal metabolic rate during their active state while they enter deep sleep to conserve energy in their inactive state⁴.

Daily torpor is common to small animals whose ambient temperature drops quickly. You can compare daily torpor to a power nap humans take to replenish their energy. Torpor can also be seasonal and occasional, depending on the environmental temperatures.  

Waking up from torpor can be jarring for many animals. The process expends a lot of energy and involves violent shaking and muscle contractions. However, the energy loss isn’t a problem because the energy is saved in a dormant state.  

What is hibernation?

Hibernation is a longer period of winter sleep. Animals hibernate during the winter months because of low temperatures and food scarcity. It is more difficult for animals to forage and hunt for food in freezing temperatures. 

Hibernating animals prepare for prolonged periods of extreme temperatures by storing body fat. They store fat reserves by eating as much as possible in summer. Then, they find a spot safe from predators because they will be defenseless during hibernation.

Sometimes, hibernating animals migrate a long distance to find a safe resting spot for a few weeks. The animal’s body temperature drops, and its metabolism slows as it starts conserving energy. Its heart rate also reduces with slow breathing. You can easily confuse an animal in hibernation with a dead one because they mostly look dead. 

Hibernating animals do not eat in hibernation. They have enough calories and fat stored in their body mass to survive the long period of inactivity. Their low metabolic rate burns slowly through the stored fat. As winter ends, they slowly enter their active state. Most hibernating species lose a third of their body weight during hibernation.

Hibernation becomes dangerous when hibernating species don’t have enough calories stored. They can die if they wake up prematurely or they hibernate in an unsafe spot. Predators can attack them without defenses. 

Differences Between Torpor and Hibernation

People often confuse torpor with hibernation. However, torpor and hibernation are different states of inactivity that allow animals to survive harsh weather conditions. Here are some differences between torpor and hibernation: 

1. Torpor is involuntary, while hibernation is a choice. 

Torpor is an involuntary state in smaller animals because they enter torpor as environmental conditions dictate. Small mammals often enter torpor for a few hours to maintain their body temperature or wait for food scarcity. Daily torpor also occurs when there is an increase in predators around the area.⁵ Some animals use it to protect themselves during predators' active hours.

Hibernation, on the other hand, is a voluntary activity performed by hibernating animals. They use internal and environmental cues to prepare and protect themselves from harsh environmental conditions. 

2. Hibernation lasts longer than torpor. 

 Another difference between torpor and hibernation is the duration. Torpor lasts for short periods, while hibernation lasts for several months. Mammal groups hibernate for 5 to 7 months, and torpid animals stay in torpor for several hours to a few days. 

3. Unlike torpid animals, hibernating animals do not wake up at intervals.   

Hibernators do not wake up at intervals during the regulated hypothermia sleep. They only wake near the end of the hibernation period. Torpid animals have to wake up at intervals to eat or pass waste. Hibernators don’t have to wake up to look for food because they rely on fat reserves stored in their body.   

4. Torpid animals and hibernators have many physiological differences. 

The metabolic rate, body temperature, heart rate, and brain activities of animals in torpor and hibernation vary. The basal metabolic rate of animals in daily torpor is approximately 19%, while that of hibernators is 4%.

Hibernators have a lower body temperature. Their temperature falls between 0°C and 10 °C, while temperatures in torpor for animals reduce² to 12°C —25°C. As animals enter torpor, their brain waves reduce drastically, but not as much as those of hibernators⁶. In hibernation, brain temperatures drop to 2-3C.

Other Forms of Suspended Animation

There are other ways animals survive harsh conditions. They are brumation and estivation. Brumation is simply hibernation in reptiles and amphibians, which are cold-blooded animals that rely on the environment to regulate temperatures. 

They brumate because they can't thermoregulate during winter seasons. Their body shuts down and lies dormant until the warmer season. Reptiles don't need to drink, eat, defecate, or move around a lot during brumation.

However, some reptiles have periods of activity during brumation. For instance, an alligator can come out from dormancy on warmer days to sunbathe. Brumation doesn't only occur during winter; reptiles can brumate any time of the year¹.

Estivation is a period of inactivity in warm climates and environments. It is the opposite of hibernation, where animals sleep during winter and other cold conditions. Like hibernation, estivating animals have a low body temperature, metabolic rate, and brain activity.

Estivation usually lasts for a few months or longer. Animals like turtles and sea cucumbers find cool spaces to lay dormant until the hot weather passes. During this time, animals lose weight, experience metabolic inhibition, and have other immune system deficiencies. Luckily, they can fix these body changes once they become active.

Animals and The Ways They Conserve Energy

Species that experience torpor:

1. Hummingbirds 
2. Doves
3. Pigeons 
4. Skunks 
5. Bears 
6. Raccoons

Species that hibernate: 

1. Bats 
2. Ground squirrels 
3. Bees
4. Woodchucks 
5. Snails 
6. Shrews 

Species that brumate:  

1. Frogs 
2. Lizards 
3. Snakes 
4. Turtles 
5. Alligators 
6. Spotted salamander 

Species that experience estivation: 

1. Crabs
2. Desert tortoises 
3. Crocodiles 
4. Mosquitoes
5. Dwarf lemur 
6. Lady beetles
7. Bogong moths 
8. Water-holding frog
9. Western swamp turtle 
10. African lungfish  

Conclusion   

Torpor appears in small birds and small mammals and lasts only a few days. Hibernation lasts longer and includes a higher state of dormancy than torpor. Animals like arctic squirrels and bats hibernate, while bears go torpid.