Critter Science

The Science of Animals

Hibernation and Brumation

A Comparison of Hibernation and Brumation

When I would teach outdoor programs in the winter I’d always try to educate the audience on the differences between hibernating and brumating animals. See below for more information on this.

Hibernation and brumation are really very closely related, they are periods of dormancy during which an animal becomes physiologically less active, their metabolic processes slow down, and growth stops. However, mammals and reptiles go into dormancy is slightly different ways, thus the terms hibernation and brumation. Here’s a quick comparison chart:

Hibernation (Mammals)Brumation (Reptiles)
Caused by shortening day length and temperature changesYESYES
Animal may feed heavily before entering dormancyYESYES
Build up of fat reserve and lipids before entering dormancy?YESYES
Feeding and eating stop during dormancyYESYES
Drinking Water StopsYESNo
Decreased heart rate, body temperature, and metabolism slow or decreaseYESYES
Use stored fat for energy during dormancyYESYES/NO (glycogen)
Anoxia Tolerant (low oxygen)NOYES
True SleepYESNo
Punctuated ActivityNO (most)YES

Timing is everything

How do animals know that it’s time to go into hibernation or brumation? There are two sets of factors, endogenous and exogenous. Endogenous cues are biotic and come from inside the animal (hormonal cues, circadian rhythms, etc) and exogenous cues are mostly abiotic and come from outside the animal (photoperiod, temperature, barometric pressure, humidity, etc.). Once certain cues are given then the animal prepares for dormancy (LLL Reptile).


Reptiles and amphibians prepare for dormancy by eating more. They build up fat reserves in their bodies that can help them survive. Unlike mammals, the reptiles also build up a high level of glycogen in their body tissues as well. Glycogen is a form of polysaccharide or sugar that can be used as energy for muscles. When mammals enter hibernation they rely solely on their fat reserves as energy to see them through winter. However, reptiles do not use fat as their sole source of energy. They mostly use the glycogen in their muscles with their fat reserves playing a greater role in reproduction, egg development, and post dormancy mating (Copeia, Gafney and Fitzpatrick, 1973; Integrative and Comparative Biology, Fitzpatrick 1976). It’s even thought that some reptiles need brumation to trigger reproductive processes such as egg and sperm production.

Slowing Down

Both reptiles and mammals slow their metabolic processes down significantly during dormancy, but reptiles are better suited for low oxygen environments during this time. Mammals slow their breathing or respiration rates down, but they still need a specific amount of oxygen saturation to survive. On the other hand, reptiles can tolerate reduced levels of oxygen, because of the glycogen in their blood. This is particularly handy because many reptiles bury themselves in the mud or under water, which can have changing or very low oxygen levels (Annual Review of Physiology, Bickler and Buck 2007).

Sleeping and Resting

Another big difference between hibernating mammals and brumating reptiles is that mammals sleep for the duration of their dormancy. Reptiles don’t really sleep, they just go into a period of dormancy that is punctuated with periods of activity. If there is a nice warm winter day they may crawl out on a log to sun or bask and then return to their hibernaculum or dormancy location. Unlike mammals reptiles must drink water during their dormancy period because hey need to avoid dehydration, this is a major part of their need to punctuate their dormancy with activity.

Confusion Solved

Hibernation and brumation are confusing terms that are often used incorrectly. In fact, there are very few animals that truly hibernate (chipmunks are one example). Most animals go into periods of long sleep with brief waking, like bears (but that’s a post for another time). The differences between truly hibernating mammals and brumating reptiles are actually quite significant. Hopefully you can now speak about this when walking around in the woods.

Source: K. McDonald: Infinite Spider Blog