Sleep Champions: Which Animals Sleep the Most and Least?

Sleep duration varies enormously across the animal kingdom, from species that sleep only a couple of hours per day to those that sleep twenty hours or more. This article examines the evidence on animal sleep duration, the ecological and physiological factors that shape it, and what these patterns mean for understanding sleep in humans. The analysis draws on comparative sleep research spanning over 150 species, including invertebrates, fish, amphibians, reptiles, birds, and fourteen orders of mammals. For farmers, animal caretakers, and life-science professionals, understanding species-specific sleep needs has direct implications for housing, feeding schedules, welfare assessment, and handling practices.

At a Glance: Sleep Duration Across Representative Species

The table below summarizes sleep duration findings from comparative sleep research. These figures represent averages from laboratory and field studies and should be interpreted as ranges instead of fixed values.

The range of spontaneous daily sleep across mammal species spans from about 2 hours to 20 hours. This variation provides important insights into sleep function without the confounding effects of sleep deprivation studies. Sleep duration across species is associated with ecological niche and feeding requirements, indicating a role for wake-sleep balance in food acquisition and energy conservation.

The Comparative Study of Animal Sleep

Historical Foundations of Sleep Duration Research

Systematic examination of sleep duration across animal species began with behavioral observation and later incorporated electrographic methods. A foundational review published in 1984 examined sleep duration in over 150 animal species, including invertebrates, fish, amphibians, reptiles, birds, and fourteen orders of mammals. The authors annotated almost 200 studies, documenting the number of animals used, photoperiod employed, sleep duration per twenty-four hours, and placement of the sleep period within the day-night cycle. Both behavioral and electrographic studies were reviewed, as were laboratory and field studies.

This early comparative work established that sleep duration is a primary index for examining sleep function. The placement of sleep within the twenty-four hour day is equally important. Nocturnal species sleep during daylight hours, diurnal species sleep at night, and crepuscular species are active around dawn and dusk. These patterns reflect evolutionary adaptations to ecological demands.

Methodological Considerations in Measuring Animal Sleep

Measuring sleep duration across species presents significant methodological challenges. Laboratory conditions may not reflect natural sleep patterns. The 1984 review highlighted several methodological issues that affect the measurement of sleep duration, including the number of animals used, the photoperiod employed, and whether measurements come from behavioral or electrographic studies.

Behavioral sleep is typically defined as a period of quiescence with a characteristic posture and reduced responsiveness to external stimuli. Electrographic sleep requires brain wave monitoring, which is more precise but more invasive. Field studies offer ecological validity but lack the controlled conditions of laboratory research. Each approach has limitations, and reported sleep durations should be understood as estimates instead of absolute values.

The Ecological Niche Hypothesis

A 2022 review in The Lancet Neurology examined sleep function from an evolutionary perspective. The authors noted that sleep duration is not related to brain size or cognitive ability. Instead, sleep duration across species is associated with their ecological niche and feeding requirements. This finding supports the view that wake-sleep balance plays a role in food acquisition and energy conservation.

Large herbivores such as horses and giraffes spend substantial time grazing and must remain vigilant against predators. Their sleep duration is correspondingly short. Small predators such as domestic cats can afford longer sleep periods because they obtain concentrated nutrition from prey and face fewer predation risks. Bats, which expend enormous energy during short foraging flights, sleep extensively during the day in protected roosts.

Sleep Duration Extremes: The Longest Sleepers

Bats and Other High-Duration Sleepers

Among mammals, insectivorous bats are consistently reported as sleeping the longest, with durations approaching 20 hours per day. Several factors explain this extreme sleep requirement. Bats have high metabolic rates during flight, which is energetically costly. They forage in short bursts and spend the remainder of the day in roosts where they are relatively safe from predators. The combination of high energy expenditure during wakefulness and low predation risk during sleep permits extended sleep periods.

Other long-duration sleepers include small rodents, opossums, and some primates. The common pattern among these species is a diet that provides concentrated nutrition, a relatively safe sleeping site, and a body size that does not require constant feeding.

Sleep in Domestic Cats

Domestic cats sleep approximately 12 to 16 hours per day, though this varies with age, health, and environmental conditions. Cats are crepuscular predators, meaning they are most active at dawn and dusk. Their sleep is polyphasic, occurring in multiple bouts throughout the day and night. Kittens and senior cats typically sleep more than young adults.

For cat owners and veterinary professionals, recognizing normal feline sleep patterns is important for distinguishing healthy behavior from lethargy associated with illness. A cat that suddenly sleeps more than usual, or less than usual, may require veterinary assessment.

REM Sleep Distribution Across Animal Groups

The 2022 evolutionary review also examined rapid eye movement sleep across homeotherm orders. Average daily REM sleep time is negatively correlated with average body and brain temperature. The largest amount of REM sleep occurs in egg-laying monotreme mammals, with moderate amounts in pouched marsupial mammals, lower amounts in placental mammals, and the lowest amounts in birds.

This pattern suggests that REM sleep may have a key role in the regulation of temperature and metabolism of the brain during sleep and in the facilitation of alert awakening. The relationship between body temperature and REM sleep distribution provides clues about the evolutionary origins of sleep stages.

Sleep Duration Extremes: The Shortest Sleepers

Large Herbivores and Grazing Demands

Large herbivores are among the shortest sleepers in the animal kingdom. Horses sleep approximately 3 to 5 hours per day, and giraffes sleep as little as 2 hours. These species face constant pressure to forage because plant material is relatively low in caloric density. They must spend most of their waking hours eating to meet energy demands.

Predation risk also shapes sleep duration in herbivores. Species that cannot retreat to safe sleeping sites must remain vigilant even during rest. This vigilance limits both total sleep time and the depth of sleep achieved. The sleep that does occur is often fragmented into short bouts.

Sleep in African Ungulates

Research on nocturnal behavior in African ungulates in zoos has highlighted the importance of understanding sleep for animal welfare. Most ungulates are diurnal or crepuscular, and their behavior differs significantly between day and night. However, many studies examine animal behavior during the day, leaving limited information on nocturnal behavior, including sleep.

Sleep behavior, especially the proportion of REM sleep, is of great importance for the well-being of an individual. Zoo managers and wildlife caretakers should consider nocturnal observation as part of welfare assessment. Automated analysis tools, such as deep-learning software packages, are being developed to facilitate long-term behavioral monitoring of ungulates in captivity.

Sleep in Wild Japanese Macaques

Social relationships influence sleep duration in some primate species. A study of wild Japanese macaques found that sleep duration is affected by social relationships among sleeping partners. Macaques that slept in proximity to preferred social partners achieved different sleep durations than those sleeping alone or with less preferred partners.

This finding has implications for captive primate management. Social housing arrangements may influence sleep quality and duration. Caretakers should consider social dynamics when designing sleeping areas and group compositions.

Factors That Shape Sleep Duration Across Species

Body Size and Metabolic Rate

Body size correlates with sleep duration in complex ways. Smaller animals generally have higher metabolic rates and may require more sleep for energy conservation. However, small body size also increases predation risk, which may limit sleep. The relationship between body size and sleep duration is therefore mediated by ecological factors.

The 2022 evolutionary review emphasized that sleep duration is not related to brain size or cognitive ability. This finding challenges assumptions that animals with larger brains or greater cognitive capacity require more sleep. Instead, ecological niche and feeding requirements are the primary determinants of sleep duration across species.

Diet and Feeding Strategy

Diet strongly influences sleep duration. Carnivores and insectivores typically sleep more than herbivores because their food is nutritionally concentrated and requires less time to obtain. Herbivores must spend extensive time grazing or browsing to meet energy requirements, leaving less time for sleep.

The 2022 review noted that consideration of the duration of spontaneous daily sleep across species of mammals, which ranges from 2 hours to 20 hours, can provide important insights into sleep function without the stress of deprivation. The association between sleep duration and feeding requirements indicates a role for wake-sleep balance in food acquisition and energy conservation.

Predation Risk and Sleeping Site Safety

Predation risk is a major determinant of sleep duration and sleep architecture. Species that sleep in safe sites, such as tree cavities, burrows, or roosts, can achieve longer and deeper sleep. Species that must sleep in exposed locations face constant threat and achieve shorter, more fragmented sleep.

The ability to choose a safe sleeping environment is also relevant to captive animal welfare. The 2021 study on African lion cub welfare in wildlife-interaction tourism identified the inability for cubs to choose their own environment and retreat from forced interaction as a leading welfare concern. Providing animals with control over their sleeping environment supports natural sleep behavior.

Social Factors

Social relationships influence sleep in group-living species. The Japanese macaque study demonstrated that social bonds affect sleep duration. Animals that sleep in proximity to preferred partners may experience reduced vigilance and improved sleep quality.

In captive settings, social housing decisions should account for sleep needs. Overcrowding or incompatible social groupings may disrupt sleep and contribute to welfare problems. The lion cub welfare study identified poor social grouping of cubs as a leading welfare concern in wildlife-interaction tourism.

Sleep in Humans: Comparative Context

Optimal Sleep Duration in Adults

Prospective epidemiological studies in industrial societies indicate that 7 hours of sleep per night in people aged 18 years or older is optimum, with higher and lower amounts of sleep predicting a shorter lifespan. Humans living a hunter-gatherer lifestyle sleep for 6 to 8 hours per night, with the longest sleep durations in winter.

The prevalence of insomnia in hunter-gatherer populations is low, around 2 percent, compared with the prevalence of insomnia in industrial societies, around 10 to 30 percent. This difference suggests that aspects of modern life, including irregular schedules and environmental factors, contribute to sleep problems.

Sleep Duration and Metabolic Health

Sleep duration has significant implications for metabolic health. A 2010 review in Endocrine Development examined the role of sleep and sleep loss in hormonal release and metabolism. The authors noted that adults and children sleep less than they did a few decades ago, and that sleeping as little as possible is often seen as an admirable behavior in contemporary society.

Accumulating evidence from epidemiologic studies and well-controlled laboratory studies indicates that chronic partial sleep loss may increase the risk of obesity and weight gain. Sleep restriction results in metabolic and endocrine alterations, including decreased glucose tolerance, decreased insulin sensitivity, increased evening concentrations of cortisol, increased levels of ghrelin, decreased levels of leptin, and increased hunger and appetite.

Sleep Duration and Type 2 Diabetes Risk

A 2024 cohort study published in JAMA Network Open investigated the associations of diet and sleep duration with the development of type 2 diabetes. The study analyzed data from 247,867 participants in the UK Biobank with a median follow-up of 12.5 years. Participants were categorized into four sleep duration groups: normal (7 to 8 hours per day), mild short (6 hours per day), moderate short (5 hours per day), and extreme short (3 to 4 hours per day).

The analysis indicated a significant increase in the risk of type 2 diabetes among participants with 5 hours or less of daily sleep. Individuals sleeping 5 hours per day exhibited a 1.16 adjusted hazard ratio, and individuals sleeping 3 to 4 hours per day exhibited a 1.41 adjusted hazard ratio. These findings underscore the importance of adequate sleep for metabolic health.

Sleep Irregularity and Cardiometabolic Disease

A 2025 review in Circulation Research examined sleep irregularity and circadian disruption as risk factors for cardiometabolic disease. Sleep irregularity, characterized by inconsistent sleep patterns from day to day, has become increasingly prevalent in modern society. The preponderance of evidence supports that sleep irregularity is a robust risk factor for obesity, metabolic syndrome, diabetes, cardiovascular disease, and mortality.

In some cases, sleep irregularity may be a more significant predictor than other widely studied sleep factors, such as sleep duration. The review noted key limitations in the current literature, including the lack of standardized measures for assessing sleep irregularity and the scarcity of intervention studies.

Practical Assessment of Sleep in Farm and Captive Animals

Observational Protocols

Assessing sleep duration in farm and captive animals requires systematic observation. For species that are active during the day, nocturnal observation is necessary to capture complete sleep patterns. Video recording with infrared capability allows continuous monitoring without disturbing animals.

The development of automated analysis tools, such as the BOVIDS software package for ungulates, demonstrates the potential for technology-assisted behavioral monitoring. These tools allow automatic evaluation of video material and can facilitate long-term studies with large sample sizes.

Recording Sleep Behavior

When recording sleep behavior, document the following parameters:

• Time of sleep onset and offset for each sleep bout
• Total sleep duration per 24-hour period
• Posture during sleep, including whether the animal is standing or lying
• Eye state, where visible, to distinguish REM from non-REM sleep
• Environmental conditions, including temperature, light, and noise
• Social context, including proximity to other animals

These records provide baseline data for detecting deviations that may indicate health or welfare problems.

Distinguishing Normal Variation from Abnormal Sleep

Sleep duration varies with age, health status, and environmental conditions. Young animals typically sleep more than adults. Sick or injured animals may sleep more or less than usual. Seasonal changes in day length can affect sleep patterns.

Professional escalation is warranted when sleep patterns change suddenly, when an animal appears unable to sleep despite opportunity, or when sleep deprivation signs such as excessive daytime drowsiness or impaired coordination are observed. Consult a veterinarian when sleep disturbances persist or are accompanied by other clinical signs.

Common Failure Patterns in Sleep Management

Inadequate Sleeping Sites

A common failure in captive animal management is providing inadequate sleeping sites. Animals need safe, comfortable locations where they can sleep without disturbance. The lion cub welfare study identified the inability for cubs to choose their own environment and retreat from forced interaction as a major welfare concern.

For farm animals, provide clean, dry bedding and protection from weather extremes. For zoo animals, provide species-appropriate sleeping platforms, dens, or shelters that allow animals to control their exposure to visitors and conspecifics.

Disrupted Circadian Rhythms

Artificial lighting can disrupt circadian rhythms in captive animals. Continuous lighting, irregular light-dark cycles, and light exposure during the dark phase can interfere with sleep. The 2025 Circulation Research review highlighted the health consequences of circadian disruption in humans, and similar principles apply to animals.

Maintain consistent light-dark cycles that approximate natural conditions for the species. For nocturnal species, minimize light exposure during the active phase. For diurnal species, ensure adequate darkness during the sleep period.

Social Stress and Sleep Disturbance

Social stress can significantly disrupt sleep. The Japanese macaque study demonstrated that social relationships affect sleep duration. Incompatible social groupings, overcrowding, or unstable dominance hierarchies can increase vigilance and reduce sleep quality.

Assess social dynamics when sleep problems are observed. Consider whether animals have opportunities to choose sleeping partners or retreat from social conflict. The lion cub welfare study identified poor social grouping as a leading welfare concern in interaction facilities.

Forced Activity During Rest Periods

Forcing animals to be active during their natural rest periods disrupts sleep and can have welfare consequences. The lion cub welfare study identified forced interaction as a major concern in wildlife-interaction tourism. Animals should have opportunities to sleep undisturbed during their natural sleep periods.

For farm animals, schedule handling, transport, and procedures during active periods when possible. For zoo animals, limit visitor interactions during rest periods and provide retreat areas where animals cannot be observed or disturbed.

Welfare and Safety Context

Sleep as a Welfare Indicator

Sleep behavior is increasingly recognized as an important welfare indicator. The BOVIDS research noted that sleep behavior, especially the proportion of REM sleep, is of great importance for the well-being of an individual. Changes in sleep patterns can indicate pain, stress, or illness.

Incorporate sleep observation into routine welfare assessments. Document baseline sleep patterns for individual animals or groups, and investigate deviations from baseline.

Venomous and Dangerous Species

Some species with unusual sleep patterns present specific safety considerations. Slow lorises, which are nocturnal primates, possess a two-step venom system. Research on slow and pygmy lorises has documented the only confirmed two-step venom system in mammals, with functional usages including intraspecific competition and ectoparasitic defense.

Caretakers working with venomous or otherwise dangerous species must understand their activity patterns to minimize risk. Handling should occur during appropriate phases of the activity cycle, and safety protocols should account for species-specific behaviors.

Zoonotic Disease Considerations

Sleeping sites and behaviors can influence disease transmission risks. Research on ecological countermeasures to prevent pathogen spillover has examined mechanisms linking environmental change and zoonotic spillover, using spillover of viruses from bats as a case study. Understanding the ecology of reservoir species, including their sleep and roosting behavior, is relevant to disease prevention.

For farm and captive settings, maintaining clean sleeping areas and minimizing contact between wildlife and domestic animals reduces disease transmission risks.

Limitations of Sleep Duration Research

Measurement Challenges

Sleep duration measurements vary with methodology. Behavioral observation may overestimate sleep by including quiet wakefulness. Electrographic recording provides more precise data but is invasive and may alter sleep patterns. Laboratory conditions may not reflect natural sleep.

The 1984 review of animal sleep noted several methodological issues that affect the measurement of sleep duration. These include the number of animals used, the photoperiod employed, and whether measurements come from behavioral or electrographic studies. Reported durations should be interpreted as estimates.

Species Variation Within Groups

Sleep duration varies within species as well as between species. Age, health status, reproductive state, and environmental conditions all influence sleep. A single average value for a species may not represent the range of normal variation.

When using published sleep duration data for management decisions, consider the context of the original studies and the specific characteristics of the animals in your care.

Gaps in Knowledge

Many species have not been studied for sleep behavior. The 1984 review noted that most research has focused on mammals and birds, with less attention to invertebrates, fish, amphibians, and reptiles. Even among mammals, many species lack detailed sleep data.

The BOVIDS research highlighted that many studies examine animal behavior during the day, with limited information on nocturnal behavior, including sleep. This gap is particularly relevant for nocturnal and crepuscular species.

Frequently Asked Questions

What animal sleeps the most?

Insectivorous bats are consistently reported as the longest sleepers among mammals, with sleep durations approaching 20 hours per day. The combination of high energy expenditure during short foraging flights and safe roosting sites permits extended sleep. Sleep duration across species is associated with ecological niche and feeding requirements instead of brain size or cognitive ability.

What animal sleeps the least?

Large herbivores such as giraffes and horses are among the shortest sleepers, with giraffes sleeping as little as 2 hours per day and horses approximately 3 to 5 hours. These species face constant grazing demands because plant material is relatively low in caloric density, and they must remain vigilant against predators.

Why do some animals sleep so much?

Animals that sleep extensively typically have diets that provide concentrated nutrition, safe sleeping sites, and limited predation risk during rest. Bats, for example, expend enormous energy during flight and can roost in protected locations. The ecological niche hypothesis proposes that wake-sleep balance serves food acquisition and energy conservation.

Why do some animals sleep so little?

Animals that sleep little face competing demands that limit sleep opportunity. Large herbivores must spend extensive time foraging to meet energy requirements. Species that cannot retreat to safe sleeping sites must maintain vigilance even during rest. The 2022 evolutionary review noted that sleep duration across species ranges from 2 hours to 20 hours and is associated with ecological niche and feeding requirements.

Is human sleep duration similar to other animals?

Human sleep duration is moderate compared with other mammals. Prospective epidemiological studies indicate that 7 hours of sleep per night in adults is optimum, with higher and lower amounts predicting shorter lifespan. Humans living a hunter-gatherer lifestyle sleep for 6 to 8 hours per night. This is similar to other medium-sized omnivorous mammals.

Does brain size determine sleep duration?

No. The 2022 evolutionary review in The Lancet Neurology stated that sleep duration is not related to brain size or cognitive ability. Instead, sleep duration across species is associated with their ecological niche and feeding requirements. This finding challenges assumptions that animals with larger brains require more sleep.

How is animal sleep measured?

Animal sleep is measured through behavioral observation and electrographic recording. Behavioral sleep is defined by quiescence, characteristic posture, and reduced responsiveness. Electrographic sleep requires brain wave monitoring. Both laboratory and field studies contribute to knowledge of sleep duration, and each method has limitations.

Can sleep patterns indicate animal welfare problems?

Yes. Changes in sleep patterns can indicate pain, stress, or illness. Sleep behavior, especially the proportion of REM sleep, is important for individual well-being. The BOVIDS research on ungulates emphasized that sleep behavior is of great importance for well-being. Sudden changes in sleep duration or quality warrant investigation and possible veterinary consultation.

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References and Further Reading

• NCBI Literature Resources. National Center for Biotechnology Information.
• PubMed. National Library of Medicine.
• Habitual Short Sleep Duration, Diet, and Development of Type 2 Diabetes in Adults.. JAMA network open, 2024.
• Sleep function: an evolutionary perspective.. The Lancet. Neurology, 2022.
• Role of sleep and sleep loss in hormonal release and metabolism.. Endocrine development, 2010.
• Sleep Irregularity, Circadian Disruption, and Cardiometabolic Disease Risk.. Circulation research, 2025.
• GABA and l-theanine mixture decreases sleep latency and improves NREM sleep.. Pharmaceutical biology, 2019.
• Lavender improves sleep through olfactory perception and GABAergic neurons of the central amygdala.. Journal of ethnopharmacology, 2025.
• Animal sleep: a review of sleep duration across phylogeny.. Neuroscience and biobehavioral reviews, 1984.
• Sleep and epilepsy.. Epilepsia, 1985.
• Why humans evolved blue eyes.. 2025.
• Slowly Making Sense: A Review of the Two-Step Venom System within Slow (Nycticebus spp.) and Pygmy Lorises (Xanthonycticebus spp.).. 2023.
• Ecological countermeasures to prevent pathogen spillover and subsequent pandemics.. 2024.
• Prior Exposure and Toddlers' Sleep-Related Memory for Novel Words.. 2021.
• Identification and Evaluation of African Lion (Panthera leo) Cub Welfare in Wildlife-Interaction Tourism.. 2021.
• The Use and Potential of Biomedical Detection Dogs During a Disease Outbreak.. 2022.
• Nocturnal behavior of African ungulates in zoos by the development of a deep-learning based software package, named BOVIDS
• An introduction to artificial intelligence in sleep medicine. 2021.
• Highly repetitive space-use dynamics in parrotfishes. Coral reefs, 2022.
• Cerebellar Gray Matter Volume, Executive Function, and Insomnia: Gender Differences in Adolescents. Scientific Reports, 2019.
• Early stages of Parkinson’s disease: comparative characteristics of sleep-wakefulness cycle in patients and model animals. Human Physiology, 2015.
• Sleep stages in the "encéphale isolé" cat. III. A quantitative and comparative study of wakefulness-sleep cycles in the "semi-chronic" "encéphale isolé" preparation. Electroencephalography and Clinical Neurophysiology, 1975.
• Sleep duration is affected by social relationships among sleeping partners in wild Japanese macaques. Behavioural Processes, 2014.

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