Hibernation Or Brumation: Which Term Is Right For Reptiles?

Hibernation or brumation, what’s the difference between these two terms, and how did “brumation” come about?

Hibernation is “the condition or period of an animal or plant spending the winter in a dormant state” (Oxford Languages).

Wilbur Mayhew did not feel that the word hibernation clearly defined the dormancy reptiles go through during winter. In 1965 Mayhew proposed the introduction of the term brumation. In his research on horned lizards (Phrynosoma mcallii), Mayhew demonstrated how they handle winter dormancy compared to mammals and birds. His research showed that reptiles experience dormancy in a very different way than mammals and birds do. Here’s why:

Hibernation Or Brumation: Key Differences

To answer whether a reptile goes into hibernation or brumation, Mayhew explored:

• Hibernation or Brumation – Body Temperature:
  • Hibernation (Heterotherms – Mammals and Birds): Hibernating animals like bears and squirrels can control their body temperature, lowering it to a stable, cooler level while they “sleep” through the winter.
  • Brumation (Reptiles): Reptiles, like bearded dragons and lizards, cannot control their body temperature. Instead, their body temperature matches their environment. This means that when the air or ground gets colder, so does the reptile. Mayhew noted that even at relatively warm winter temperatures, reptiles in brumation continue to show reduced metabolic activity. This ability helps them conserve energy despite their reliance on external temperatures.
• Hibernation or Brumation – Metabolism:
  • Hibernation: Mammals slow down their heart rate and reduce their metabolism to save energy, but they still manage to keep their bodies working at a lower level by regulating temperature.
  • Brumation: Reptiles also slow down their metabolism, but in a way that is even more dependent on the temperature around them. Mayhew’s study showed that reptiles, like a bearded dragon in hibernation, experience lower metabolic rates even when external temperatures fluctuate. For example, horned lizards in his research maintained metabolic reductions even at temperatures as high as 35°C. This helps them save energy during dormancy. For example, a bearded dragon in hibernation would use significantly less energy during this state.
• Hibernation or Brumation – Triggers for Dormancy
  • Hibernation: Mammals and birds hibernate primarily in response to colder temperatures and food scarcity.
  • Brumation: Reptiles brumate not just because of cold, but also because of changes in daylight and seasonal cues. Mayhew discovered that lizards held at a steady, warm temperature of 35°C in winter still became dormant. This shows that cold isn’t the only trigger—changes in light and seasonal patterns are equally important. For example, horned lizards demonstrated consistent anorexia (loss of appetite) before entering dormancy, regardless of temperature. This seasonal anorexia is a signal for the onset of brumation. Of course, this is also true for a bearded dragon in hibernation​.

Hibernation Or Brumation: Why Did Mayhew Propose The New Term?

Mayhew felt that using the word hibernation for reptiles was misleading because it implied reptiles managed their body temperature like mammals, which isn’t true. Instead, he proposed the term brumation to describe how reptiles enter dormancy without controlling their body heat. Unlike mammals, reptiles cannot regulate their body temperature internally, so their dormancy is driven by external environmental factors. Reptiles, like bearded dragons, rely entirely on external factors like temperature and daylight to signal when it’s time to slow down and conserve energy.

In his subsequent research papers, Mayhew commenced using the term brumation, such as in 1970 in “Seasonal changes in testicular histology of three species of the lizard genus Uma.” He also used it in an article for Herpetologica, and by 1973, other researchers like Gaffney and Fitzpatrick had also started using it. However, researchers Pianka and Parker (1975) continued to use the term hibernation in lizards despite referencing Mayhew’s 1965 research. The very research that proposed the new term brumation! To this day, researchers still use both terms, referring to either brumation or hibernation.

Conclusion: Brumation Or Hibernation For Reptiles

To be clear, it is not really a question of hibernation or brumation. Hibernation describes the behavior, whereas brumation describes the physiological shift.

The research on hibernation or brumation helped establish brumation as an appropriate term for reptile dormancy. Mayhew emphasizes the differences in physiological processes between reptiles and mammals during their respective winter dormancy. Mayhew’s detailed observations of the horned lizard’s behavior and physiological changes, like their ability to maintain dormancy at various temperatures, provided the foundation for understanding reptile brumation.

Researchers tend to use hibernation, but not always, whereas reptile enthusiasts have gravitated towards brumation. The Obligate Scientist (Paul) wrote an article titled “Do Reptiles Hibernate or Brumate?” which inspired this article. In his article, he also discusses researchers who disagree with using the term brumation. See more in his post.

References

Brumal. (n.d.). Vocabulary.com Dictionary; IXL Learning.

Definition of BRUMATION. (2008, November). Merriam-Webster; Merriam-Webster.

Gaffney, F. G., & Fitzpatrick, L. C. (1973). Energetics and Lipid Cycles in the Lizard, Cnemidophorus tigris. Copeia, 1973(3), 446.

Mayhew, W. W. (1965). Hibernation in the horned lizard, Phrynosoma m’calli. Comparative Biochemistry and Physiology, 16(1), 103–119.

Mayhew, W. W., & Wright, S. J. (1970). Seasonal changes in testicular histology of three species of the lizard genusUma. Journal of Morphology, 130(2), 163–185.

Mayhew, W. W. (1971). Reproduction in the Desert Lizard, Dipsosaurus Dorsalis. Herpetologists’ League. Herpetologica, 27, 57-77.

Pianka, E. R., & Parker, W. S. (1975). Ecology of Horned Lizards: A Review with Special Reference to Phrynosoma platyrhinos. Copeia, 1975(1), 141.