Beyond Hibernation: Estivation and Brumation Explained

Hibernation is the most familiar form of animal dormancy, but it is not the only one. Estivation is a state of dormancy that animals enter to survive hot, dry conditions, while brumation is a state of dormancy that reptiles enter during cold winter months. This article explains the biological differences among hibernation, estivation, and brumation, describes the physiological mechanisms that make each state possible, and provides practical guidance for farmers, wildlife rehabilitators, and animal keepers who manage animals that undergo these dormancy states.

What Are the Three Major Forms of Animal Dormancy

Animal dormancy is a reversible state of reduced metabolic activity that allows an animal to survive conditions that would otherwise be lethal. The three major forms are hibernation, estivation, and brumation. Hibernation is a winter dormancy state used by endotherms, or warm-blooded animals, to survive cold temperatures and scarce food. Estivation is a summer dormancy state used by both endotherms and ectotherms to survive heat and drought. Brumation is a winter dormancy state used by ectotherms, or cold-blooded animals, particularly reptiles, to survive cold temperatures when their body temperature would otherwise drop too low for normal activity.

The distinction between hibernation and brumation matters for animal care. A mammal in hibernation maintains a regulated body temperature above ambient temperature and periodically arouses to drink or shift position. A reptile in brumation does not maintain a regulated body temperature and may not move for weeks at a time. The distinction between hibernation and estivation matters for understanding seasonal management. An animal that estivates in summer requires different environmental conditions than one that hibernates in winter.

At a Glance

The table below compares the three dormancy states across key biological and management variables.

The Biology of Metabolic Rate Depression

All three dormancy states depend on facultative metabolic rate depression, which is the ability of an animal to voluntarily lower its metabolic rate far below its normal resting level. This strategy is common among molluscs and enables animals to survive for days or even months without oxygen or under extremely dry conditions. The large reductions in metabolic rate during estivation and anoxia translate into considerable energy savings when dormant animals are compared to active animals. A complex metabolic coordination is required during the transition into the dormant state to maintain cellular homeostasis and involves both energy-consuming and energy-producing pathways. Enzyme phosphorylation is one mechanism that controls metabolic flux, and phosphorylated enzymes exhibit altered substrate, activator, and inhibitor affinities. Changes in the concentrations of allosteric effectors such as fructose 2,6-bisphosphate also occur during hypometabolic states. These molecular changes allow an animal to shift from a high-energy active state to a low-energy dormant state without damaging its cells. The NCBI Literature Resources and PubMed databases contain extensive research on these mechanisms.

How Metabolic Suppression Protects Cells

Fasting is a component of many species' life history due to environmental factors or behavioral patterns that limit access to food. Despite the metabolic and physiological challenges associated with these life history stages, fasting-adapted wild vertebrates exhibit few if any signs of oxidative stress, suggesting that fasting promotes redox homeostasis. A review of mammalian, avian, reptilian, amphibian, and piscine examples of animals undergoing fasting during prolonged metabolic suppression such as hibernation and estivation shows largely beneficial effects of fasting on redox balance via limited oxidative damage. Fasting wild vertebrates buffer themselves from the negative consequences of oxidative damage through specific strategies such as elevating antioxidants, selectively maintaining redox balance in critical tissues, or modifying behavioral patterns. This research is documented in Fasting ameliorates oxidative stress: A review of physiological strategies across life history events in wild vertebrates.

The Preparation for Oxidative Stress Strategy

Organisms adapted to environmental stressors such as freezing, dehydration, salinity variations, hypoxia, or anoxia often reduce their metabolic rates to maximize their chances of survival. Upon recovery of environmental conditions and basal metabolic rates, cells are affected by an oxidative burst that, if uncontrolled, leads to oxidative cell damage and eventually death. A number of adapted organisms are able to increase their antioxidant defenses during an environmental or functional hypoxic transgression, a strategy interpreted in the 1990s as a preparation for oxidative stress. Since that time, preparation for oxidative stress mechanisms have been identified in at least 83 animal species representing different phyla including Cnidaria, Nematoda, Annelida, Tardigrada, Echinodermata, Arthropoda, Mollusca, and Chordata. This research is summarized in Twenty years of the Preparation for Oxidative Stress theory: Ecophysiological advantages and molecular strategies.

The practical implication for animal keepers is that the transition into dormancy and the transition out of dormancy are biologically stressful periods. An animal that appears healthy during dormancy may still face oxidative damage during arousal. Management protocols should minimize disturbance during dormancy and should ensure that the animal has adequate antioxidant support through proper nutrition before entry and after emergence.

Estivation in Mammals

Estivation in mammals is less common than hibernation but occurs in several rodent species and some primates. The edible dormouse, Glis glis, provides a well-documented example. Biologists generally accept that multiday torpor is primarily a response to adverse environmental conditions, namely cold climate and low food abundance. However, research on the edible dormouse shows that hibernation is not primarily driven by poor conditions in this species. Dormice enter torpor with fat reserves in years that are unfavorable for reproduction but provide ample food supply for animals to sustain themselves and even gain body energy reserves. While staying in hibernacula below ground, hibernators have much higher chances of survival than during the active season. Researchers think that dormice enter prolonged torpor predominantly to avoid predation, mainly nocturnal owls. Because estivation in summer is immediately followed by hibernation, this strategy requires a good body condition in terms of fat reserves. As dormice age, they encounter fewer occasions to reproduce when calorie-rich seeds are available late in the year, and they phase advance the hibernation season. By early emergence from hibernation, the best territories can be occupied and the number of mates maximized. However, this advantage comes at the cost of increased predation pressure that is maximal in spring. This research is documented in Why hibernate? Predator avoidance in the edible dormouse.

The practical lesson from this research is that dormancy is not always a simple response to environmental hardship. For some species, dormancy is a predator avoidance strategy that requires careful body condition management. An animal keeper who assumes that a fat animal will not enter dormancy may be incorrect. Species-specific knowledge is essential.

Estivation in Amphibians

Amphibians are among the most studied estivating animals because many species face seasonal drought. The green striped burrowing frog, Cyclorana alboguttata, enters a reversible hypometabolic state called aestivation where heart rate and oxygen consumption can be reduced despite warm ambient temperatures above 25 degrees Celsius. Research using mRNA sequencing of aestivating versus control gastrocnemius muscle indicates extensive metabolic reprogramming, with nearly a quarter of the entire transcriptome exhibiting a nominal greater than 2-fold change. Carbohydrate catabolism was systemically downregulated, consistent with a physiological adaptation to spare carbohydrate reserves. A 630-fold downregulation of ENO3 encoding the enolase enzyme was most striking. The mRNA encoding the mitoproteome were significantly downregulated during aestivation, including members of the TCA cycle, electron transport chain, ATP synthase complex, and ADP/ATP intracellular transport. Most prominent among the upregulated mRNA are those encoding aspects of regulated proteolysis including the proteosome, peptidases, atrogins, and ubiquitination. The skeletal musculature is poised for accelerated translation of mRNA upon emergence, supporting a strategy to rapidly restore function when the summer drought ends. This research is documented in Dramatic genome-wide reprogramming of mRNA in hypometabolic muscle.

Urea and Water Conservation in Estivating Amphibians

Amphibians that estivate in dry conditions face a serious challenge of water loss. Some species accumulate urea, which helps retain water and may protect enzymes from the effects of high salt concentrations. The Urea and salt effects on enzymes from estivating and non-estivating amphibians study examined how urea and salts affect enzymes from estivating and non-estivating amphibians. The practical implication is that estivating amphibians should not be disturbed during dormancy because the transition to activity requires careful physiological adjustments.

The African Lungfish as an Extreme Example

African dipnoi, or lungfish, are aestivating fish and obligate air breathers that undergo remarkable morpho-functional organ readjustment from biochemical to morphological level throughout their complex life cycle. Research on African lungfish of the genus Protopterus has examined the changes of the NOS/NO system in lungs, gills, kidney, heart, and myotomal muscle in relation to the switch from freshwater to aestivation and vice versa. The expression and localization patterns of NOS and its protein partners Akt, Hsp-90, and HIF-1 alpha have been discussed together with the apoptosis rate. These molecular components are crucial in signalling transduction and integration networks induced by environmental challenges such as temperature, dehydration, and inactivity experienced at the beginning, during, and at the end of the dry season. This research is documented in The NOS/NO system in an example of extreme adaptation: The African lungfish.

Estivation in Molluscs and Invertebrates

Land snails are classic examples of estivation. Research on the biochemistry of estivation and metabolic depression in pulmonate land snails has shown that despite reduced oxygen consumption and PO2 during estivation, the activities of antioxidant enzymes such as superoxide dismutase and catalase increased in 30 day estivating snails. This appears to be an adaptation that allows the snails to deal with oxidative stress that takes place during arousal when PO2 and oxygen consumption rise rapidly. Oxidative stress was indicated by increased levels of lipid peroxidation damage products accumulating in hepatopancreas within minutes after arousal was initiated. The activation of antioxidant defenses in the organs of Otala lactea during estivation is a preparative mechanism against oxidative stress during arousal. This research is documented in Antioxidant defenses and metabolic depression. The hypothesis of preparation for oxidative stress in land snails.

The practical implication for anyone keeping snails or other estivating invertebrates is that the arousal period is a time of high oxidative stress. The animal should be allowed to arouse naturally without handling, and the enclosure should provide appropriate humidity and food immediately available upon emergence.

Brumation in Reptiles

Brumation is the term used for winter dormancy in reptiles. Unlike hibernation in mammals, brumation involves a body temperature that tracks ambient temperature instead of being regulated above it. Reptiles in brumation may not move for weeks, do not eat, and have dramatically reduced metabolic rates.

Transcriptional Regulation During Brumation

Long-term winter dormancy in ectotherms defines the annual cycle of many temperate-zone reptiles. Time-resolved transcriptomic profiles of liver and testis from male red-sided garter snakes, Thamnophis sirtalis parietalis, at five timepoints spanning the eight-month brumation cycle identified 3,715 transcripts in liver and 5,828 in testis with significant temporal expression structure organized into five overarching temporal patterns: sustained downregulation, downregulation with post-arousal recovery, sustained upregulation, brumation-specific upregulation, and cyclic modulation. Liver showed coordinated upregulation of fatty acid mobilization enzymes and gluconeogenic regulators coincident with sustained low temperatures. Testis showed sustained suppression of meiosis, reproduction, and DNA-metabolism gene sets that did not fully recover at arousal, consistent with this species' dissociated reproductive pattern. Both tissues showed coordinated upregulation of stress-response pathways involving heat-shock proteins, HIF1 alpha, and a glutathione-based antioxidant defense. This research is documented in Cold, dark, and hungry: Dynamic transcriptional regulation across eight months of brumation.

Seasonal Activity Patterns in Desert Reptiles

The spiny-tailed lizard, Uromastyx aegyptia, a vulnerable species native to the desert and semi-desert regions of the Middle East, shows clear seasonal activity patterns. Research conducted in the Ha'il region of northern Saudi Arabia revealed that soil temperature significantly affected the lizard's activity patterns. During spring, spiny-tailed lizards were more active, spending around 25 percent of the day engaged in various behaviors, while their activity decreased to less than 20 percent in summer. In autumn and winter, the lizards did not follow a consistent daily activity, becoming active only when surface temperatures exceeded 35 degrees Celsius. The absence of tracks and sightings in January suggests the species enters a state of complete brumation during this month. Human disturbance from livestock and vehicles was observed in spring and summer, and reducing this type of human-caused disturbance should be considered when designing protection programs. This research is documented in Daily and Seasonal Activity Patterns of the Spiny-tailed Lizard in Northern Saudi Arabia.

Hormone Cycles and Brumation in Snakes

Reptiles are underrepresented in endocrinology research, and most studies are conducted on lizards and turtles instead of oviparous snakes. Research on captive Louisiana pinesnakes, Pituophis ruthveni, described annual hormone cycles in an egg-laying colubrid. Fecal and blood samples were collected from adult male and female snakes throughout the year, and four hormones were measured: corticosterone, estradiol, progesterone, and testosterone. In females, neither fecal nor plasma samples showed significant differences between any of the collection periods, excepting increased levels found in female plasma progesterone PreLay compared to PostLay, demonstrating the importance of circulating progesterone in oviparous snake reproduction. In males, time played a significant role in fecal corticosterone levels. Male plasma showed a number of significant changes throughout the year, including a significant increase from Post-Brumation to Breeding levels of corticosterone and significantly higher Breeding estradiol and testosterone levels than all other time bins except Post-Brumation. This research is documented in Plasma and fecal hormone profiles in an Endangered, oviparous colubrid, the Louisiana pinesnake.

The practical implication for snake breeders is that brumation is a critical part of the reproductive cycle. Males emerge from brumation with elevated corticosterone and then show elevated reproductive hormones during the breeding season. A male that does not undergo a proper brumation period may not show normal reproductive hormone cycles.

Torpor Compared to Hibernation, Estivation, and Brumation

Torpor is a short-term state of reduced metabolic activity that lasts from a few hours to a few days. Hibernation, estivation, and brumation are long-term states that last for weeks or months. The distinction is important for management because a torpid animal can be expected to arouse quickly and resume normal activity, while a hibernating, estivating, or brumating animal requires a prolonged period of dormancy.

Torpor can occur daily in some small mammals and birds that reduce their body temperature and metabolic rate during the night to conserve energy. Hibernation is essentially a series of prolonged torpor bouts. Estivation is a summer equivalent of hibernation. Brumation is the reptilian equivalent of hibernation. The NCBI Literature Resources and PubMed databases provide access to research on all of these states.

Practical Management of Dormant Animals

Managing animals that hibernate, estivate, or brumate requires species-specific knowledge and careful record keeping. The following steps apply to most dormancy management situations.

Step 1: Confirm the Species Dormancy Type

Identify whether the species is an endotherm or ectotherm and whether it naturally hibernates, estivates, or brumates. A mammal that hibernates requires different management than a reptile that brumates. A species that estivates requires different seasonal timing than one that hibernates. Consult species-specific literature through PubMed before making management decisions.

Step 2: Assess Pre-Dormancy Body Condition

An animal entering dormancy must have adequate fat reserves and hydration. For hibernating mammals, insufficient fat reserves can be fatal. For estivating amphibians, adequate hydration before entry is critical. For brumating reptiles, the animal should be healthy and free of parasites before the cooling period begins. Weigh the animal and record its body condition score before dormancy entry.

Step 3: Control the Environment Gradually

Dormancy should not be induced suddenly. For hibernation and brumation, gradually reduce temperature and photoperiod over several weeks. For estivation, gradually reduce water availability and increase temperature. Sudden changes can cause stress and prevent the animal from entering dormancy properly.

Step 4: Monitor During Dormancy

Check dormant animals regularly but minimally. Record temperature, humidity, and any visible signs of movement or distress. For brumating reptiles, provide a shallow water dish that is checked regularly even though the animal may not drink. For estivating animals, maintain appropriate humidity to prevent lethal desiccation.

Step 5: Manage Arousal Carefully

Arousal from dormancy is a period of high oxidative stress. The animal should be allowed to arouse naturally without handling. Provide food and water immediately upon emergence. For brumating reptiles, gradually increase temperature over several days. For estivating amphibians, gradually reintroduce water.

Records and Measurements for Dormancy Management

Accurate records are essential for managing dormant animals. The following measurements should be recorded for each dormancy cycle.

Common Failure Patterns in Dormancy Management

Several common management errors lead to dormancy failure or animal death.

Inadequate Pre-Dormancy Nutrition

An animal that enters dormancy without adequate fat reserves may not survive. This is a particular risk for hibernating mammals and brumating reptiles. The animal may arouse prematurely, consume its remaining energy stores, and die before food is available.

Improper Hydration

Dehydration during dormancy is a common cause of death. Estivating animals face the greatest risk because they enter dormancy specifically to survive dry conditions. Brumating reptiles may not drink during dormancy but still require access to water. Hibernating mammals typically do not drink but may arouse to drink if conditions are too dry.

Disturbance During Dormancy

Handling or disturbing a dormant animal can cause it to arouse prematurely. Arousal consumes energy and causes oxidative stress. Repeated disturbance can be fatal. The research on preparation for oxidative stress shows that arousal is a biologically demanding period. See Preparation for oxidative stress under hypoxia and metabolic depression: Revisiting the proposal two decades later for details on the oxidative challenges of arousal.

Incorrect Temperature Management

For brumating reptiles, temperature that is too warm prevents proper brumation and causes the animal to continue metabolizing at a reduced but unsustainable rate. Temperature that is too cold can be fatal. For hibernating mammals, temperature that is too warm causes more frequent arousal and faster depletion of fat reserves.

Inadequate Veterinary Oversight

Dormancy is not a disease state, but it can mask disease. An animal that is ill before dormancy may die during dormancy. A veterinarian with experience in the species should examine the animal before dormancy entry and after arousal.

Welfare and Safety Considerations

Dormancy is a natural biological state, but it carries welfare risks when managed improperly. The primary welfare concerns are dehydration, starvation, and distress from disturbance. An animal that is unable to enter dormancy because of improper environmental conditions may continue to metabolize at a normal rate while food is unavailable, leading to starvation.

Safety considerations apply primarily to the keeper. Some dormant animals can arouse quickly and may bite or scratch when disturbed. Brumating reptiles may still strike if handled. Always use appropriate handling equipment and consult species-specific safety guidance.

Limitations of Current Knowledge

Research on dormancy is uneven across species. Hibernation in mammals is well studied. Estivation in molluscs and amphibians is moderately well studied. Brumation in reptiles is less well studied, and most research has been conducted on snakes and lizards instead of turtles and crocodilians. The PubMed database contains extensive research on hibernation and estivation but fewer studies on brumation.

The molecular mechanisms of dormancy are increasingly well understood, but the practical implications for animal management are still being developed. For example, research on the preparation for oxidative stress has identified antioxidant defense mechanisms in at least 83 animal species, but the practical application of this knowledge to dormancy management is still emerging. See Twenty years of the Preparation for Oxidative Stress theory for a review of the molecular strategies.

Professional Escalation Criteria

Consult a veterinarian or species specialist in the following situations.

Weight Loss Exceeding Expected Range

If a dormant animal loses more weight than expected for its species and dormancy duration, veterinary assessment is needed. Record the expected weight loss range before dormancy entry.

Premature Arousal

If an animal arouses from dormancy more than two weeks before the expected emergence date, veterinary assessment is needed. The animal may be ill, dehydrated, or experiencing improper environmental conditions.

No Arousal at Expected Time

If an animal does not arouse within two weeks after the expected emergence date, veterinary assessment is needed. The animal may be dead, too weak to arouse, or experiencing improper environmental conditions.

Visible Discharge or Lesions

Any visible discharge from the eyes, nose, mouth, or cloaca during dormancy requires veterinary assessment. Any skin lesions or abnormal swelling also require assessment.

Abnormal Posture or Breathing

If a dormant animal shows abnormal posture, labored breathing, or unusual movement, veterinary assessment is needed immediately.

Frequently Asked Questions

What is the difference between torpor and hibernation?

Torpor is a short-term state of reduced metabolic activity that lasts from a few hours to a few days. Hibernation is a long-term state that lasts for weeks or months and consists of a series of prolonged torpor bouts. Torpor can occur daily in some small mammals and birds, while hibernation is a seasonal state.

What is the difference between torpor and estivation?

Torpor is a short-term state of reduced metabolic activity that can occur at any time. Estivation is a long-term summer dormancy state that lasts for weeks or months and is triggered by heat and drought. An animal in torpor can arouse quickly, while an estivating animal requires a prolonged period of dormancy.

What is the difference between torpor and brumation?

Torpor is a short-term state of reduced metabolic activity that can occur in both endotherms and ectotherms. Brumation is a long-term winter dormancy state specific to ectotherms, particularly reptiles. A reptile in brumation has a body temperature that tracks ambient temperature, while a mammal in torpor maintains a regulated body temperature above ambient.

What is the difference between hibernation and estivation?

Hibernation is a winter dormancy state used by endotherms to survive cold temperatures and scarce food. Estivation is a summer dormancy state used by both endotherms and ectotherms to survive heat and drought. The edible dormouse provides an example of a mammal that uses both states, entering estivation in summer followed immediately by hibernation. See Why hibernate? Predator avoidance in the edible dormouse for details.

What is the difference between hibernation and brumation?

Hibernation is a winter dormancy state used by endotherms, or warm-blooded animals, that maintain a regulated body temperature above ambient temperature. Brumation is a winter dormancy state used by ectotherms, or cold-blooded animals, particularly reptiles, whose body temperature tracks ambient temperature. A hibernating mammal periodically arouses to drink or shift position, while a brumating reptile may not move for weeks.

What is the difference between estivation and brumation?

Estivation is a summer dormancy state triggered by heat and drought. Brumation is a winter dormancy state triggered by cold temperature and short photoperiod. Estivation is used by both endotherms and ectotherms, while brumation is used primarily by reptiles. The spiny-tailed lizard provides an example of a reptile that is active in spring, reduces activity in summer, and enters complete brumation in January. See Daily and Seasonal Activity Patterns of the Spiny-tailed Lizard for details.

Which animals estivate?

Many animals estivate, including mammals such as the edible dormouse, amphibians such as the green striped burrowing frog, fish such as the African lungfish, molluscs such as land snails, and invertebrates such as rotifers. The Dramatic genome-wide reprogramming of mRNA in hypometabolic muscle study documents estivation in the green striped burrowing frog, and the The NOS/NO system in an example of extreme adaptation: The African lungfish study documents estivation in lungfish.

How long can animals remain in dormancy?

Dormancy duration varies widely by species and environmental conditions. Some animals enter short-term torpor for hours, while others hibernate, estivate, or brumate for months. Some organisms enter long-term dormancy lasting decades or even centuries. Research on encased rotifer embryos shows that dormant embryos may remain dormant for decades, similar to plant seeds. See A transcriptomic examination of encased rotifer embryos reveals the developmental trajectory leading to long-term dormancy for details.

Related Articles

• Animal Biology
• Animal Research
• Rna Codon Chart
• Rna Codon Chart
• Rna Codon Chart

References and Further Reading

• NCBI Literature Resources. National Center for Biotechnology Information.
• PubMed. National Library of Medicine.
• Why hibernate? Predator avoidance in the edible dormouse.. Mammal research, 2023.
• Fasting ameliorates oxidative stress: A review of physiological strategies across life history events in wild vertebrates.. Comparative biochemistry and physiology. Part A, Molecular & integrative physiology, 2021.
• Twenty years of the 'Preparation for Oxidative Stress' (POS) theory: Ecophysiological advantages and molecular strategies.. Comparative biochemistry and physiology. Part A, Molecular & integrative physiology, 2019.
• The NOS/NO system in an example of extreme adaptation: The African lungfish.. Journal of thermal biology, 2020.
• Glycolytic controls in estivation and anoxia: a comparison of metabolic arrest in land and marine molluscs.. Comparative biochemistry and physiology. Part A, Physiology, 1997.
• Preparation for oxidative stress under hypoxia and metabolic depression: Revisiting the proposal two decades later.. Free radical biology & medicine, 2015.
• Antioxidant defenses and metabolic depression. The hypothesis of preparation for oxidative stress in land snails.. Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology, 1998.
• Dramatic genome-wide reprogramming of mRNA in hypometabolic muscle.. Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology, 2024.
• Cold, dark, and hungry: Dynamic transcriptional regulation across eight months of brumation. 2026.
• Plasma and fecal hormone profiles in an Endangered, oviparous colubrid, the Louisiana pinesnake.. 2025.
• Daily and Seasonal Activity Patterns of the Spiny-tailed Lizard (&lt,i&gt,Uromastyx aegyptia&lt,/i&gt,) in Northern Saudi Arabia.. 2025.
• A transcriptomic examination of encased rotifer embryos reveals the developmental trajectory leading to long-term dormancy, are they “animal seeds”?. BMC Genomics, 2024.
• Animal Models in Uveal Melanoma. Clinical ophthalmic oncology, 2019.
• Dormancy and dispersal in dimorphic achenes of tansy ragwort, Senecio jacobaea L. (Compositae). Oecologia, 1984.
• Life Cycles and Diapause. 1987.
• Urea and salt effects on enzymes from estivating and non-estivating amphibians. Molecular and Cellular Biochemistry, 1994.

This article is educational and does not replace institutional policy, professional advice, or applicable safety and regulatory requirements.