{
  "type": "fact",
  "url": "https://karelbusta.dev/data/sleep/bigger-animals-sleep-less",
  "title": "The bigger the mammal, the less it sleeps",
  "claim": "Across 83 mammal species, every tenfold increase in body weight goes with about 21% less daily sleep (log-log slope −0.103, 95% CI −0.130 to −0.075, R² = 0.40). A 1 kg mammal is predicted to sleep about 10.1 hours; a giraffe actually logs 1.9.",
  "description": "In 83 mammal species, each tenfold jump in body weight comes with ~21% less sleep. Bats sleep 20 hours, giraffes under 2.",
  "confidence": "solid",
  "published": "2026-10-14",
  "context": "Little brown bats sleep 19.9 hours a day; giraffes 1.9. Body size explains about 40% of that spread: big grazers like horses, cows and elephants sit at the bottom, small bats, opossums and rodents at the top. Savage and West tie this to metabolism: per gram, small brains run hotter, and their model treats sleep as time for repair. Two caveats matter: almost all of these numbers come from captive or laboratory animals, and wild animals can sleep very differently (wild elephants manage about 2 hours, wild sloths about 9.6 rather than the 14+ hours reported in captivity). Size is a strong trend, not a rule: the tiger (15.8 h) and the giant armadillo (18.1 h) are heavy and still sleep a lot.",
  "sources": [
    {
      "authors": "Savage VM, West GB",
      "journal": "Proceedings of the National Academy of Sciences",
      "sampleSize": "83 mammal species (sleep times compiled from Zepelin 1989)",
      "title": "A quantitative, theoretical framework for understanding mammalian sleep",
      "url": "https://doi.org/10.1073/pnas.0610080104",
      "year": 2007
    }
  ],
  "method": "Ordinary least squares fit of log10(total sleep, h/day) on log10(body weight, kg) for all 83 species in the mammal-sleep dataset, computed by this site's ingest script (apps/data/ingest/mammal-sleep/build.ts). Savage & West report the same exponent for total sleep time (about −0.1); their headline −0.16 exponent is for the ratio of sleep to waking time, not total sleep. Dropping the three whales and dolphins whose sleep the authors halved (n = 80) gives a slope of −0.096 and R² = 0.36.",
  "chart": {
    "data": [
      {
        "bodywt": 50,
        "name": "Cheetah",
        "sleep_total": 12.1
      },
      {
        "bodywt": 0.48,
        "name": "Owl monkey",
        "sleep_total": 17
      },
      {
        "bodywt": 1.35,
        "name": "Mountain beaver",
        "sleep_total": 14.4
      },
      {
        "bodywt": 0.019,
        "name": "Greater short-tailed shrew",
        "sleep_total": 14.9
      },
      {
        "bodywt": 600,
        "name": "Cow",
        "sleep_total": 4
      },
      {
        "bodywt": 3.85,
        "name": "Three-toed sloth",
        "sleep_total": 14.4
      },
      {
        "bodywt": 20.49,
        "name": "Northern fur seal",
        "sleep_total": 8.7
      },
      {
        "bodywt": 0.045,
        "name": "Vesper mouse",
        "sleep_total": 7
      },
      {
        "bodywt": 14,
        "name": "Dog",
        "sleep_total": 10.1
      },
      {
        "bodywt": 14.8,
        "name": "Roe deer",
        "sleep_total": 3
      },
      {
        "bodywt": 33.5,
        "name": "Goat",
        "sleep_total": 5.3
      },
      {
        "bodywt": 0.728,
        "name": "Guinea pig",
        "sleep_total": 9.4
      },
      {
        "bodywt": 4.75,
        "name": "Grivet",
        "sleep_total": 10
      },
      {
        "bodywt": 0.42,
        "name": "Chinchilla",
        "sleep_total": 12.5
      },
      {
        "bodywt": 0.06,
        "name": "Star-nosed mole",
        "sleep_total": 10.3
      },
      {
        "bodywt": 1,
        "name": "African giant pouched rat",
        "sleep_total": 8.3
      },
      {
        "bodywt": 0.005,
        "name": "Lesser short-tailed shrew",
        "sleep_total": 9.1
      },
      {
        "bodywt": 3.5,
        "name": "Long-nosed armadillo",
        "sleep_total": 17.4
      },
      {
        "bodywt": 2.95,
        "name": "Tree hyrax",
        "sleep_total": 5.3
      },
      {
        "bodywt": 1.7,
        "name": "North American Opossum",
        "sleep_total": 18
      },
      {
        "bodywt": 2547,
        "name": "Asian elephant",
        "sleep_total": 3.9
      },
      {
        "bodywt": 0.023,
        "name": "Big brown bat",
        "sleep_total": 19.7
      },
      {
        "bodywt": 521,
        "name": "Horse",
        "sleep_total": 2.9
      },
      {
        "bodywt": 187,
        "name": "Donkey",
        "sleep_total": 3.1
      },
      {
        "bodywt": 0.77,
        "name": "European hedgehog",
        "sleep_total": 10.1
      },
      {
        "bodywt": 10,
        "name": "Patas monkey",
        "sleep_total": 10.9
      },
      {
        "bodywt": 0.071,
        "name": "Western american chipmunk",
        "sleep_total": 14.9
      },
      {
        "bodywt": 3.3,
        "name": "Domestic cat",
        "sleep_total": 12.5
      },
      {
        "bodywt": 0.2,
        "name": "Galago",
        "sleep_total": 9.8
      },
      {
        "bodywt": 899.995,
        "name": "Giraffe",
        "sleep_total": 1.9
      },
      {
        "bodywt": 800,
        "name": "Pilot whale",
        "sleep_total": 2.7
      },
      {
        "bodywt": 85,
        "name": "Gray seal",
        "sleep_total": 6.2
      },
      {
        "bodywt": 2.625,
        "name": "Gray hyrax",
        "sleep_total": 6.3
      },
      {
        "bodywt": 62,
        "name": "Human",
        "sleep_total": 8
      },
      {
        "bodywt": 1.67,
        "name": "Mongoose lemur",
        "sleep_total": 9.5
      },
      {
        "bodywt": 6654,
        "name": "African elephant",
        "sleep_total": 3.3
      },
      {
        "bodywt": 0.37,
        "name": "Thick-tailed opposum",
        "sleep_total": 19.4
      },
      {
        "bodywt": 6.8,
        "name": "Macaque",
        "sleep_total": 10.1
      },
      {
        "bodywt": 0.053,
        "name": "Mongolian gerbil",
        "sleep_total": 14.2
      },
      {
        "bodywt": 0.12,
        "name": "Golden hamster",
        "sleep_total": 14.3
      },
      {
        "bodywt": 0.035,
        "name": "Vole",
        "sleep_total": 12.8
      },
      {
        "bodywt": 0.022,
        "name": "House mouse",
        "sleep_total": 12.5
      },
      {
        "bodywt": 0.01,
        "name": "Little brown bat",
        "sleep_total": 19.9
      },
      {
        "bodywt": 0.266,
        "name": "Round-tailed muskrat",
        "sleep_total": 14.6
      },
      {
        "bodywt": 1.4,
        "name": "Slow loris",
        "sleep_total": 11
      },
      {
        "bodywt": 0.21,
        "name": "Degu",
        "sleep_total": 7.7
      },
      {
        "bodywt": 0.028,
        "name": "Northern grasshopper mouse",
        "sleep_total": 14.5
      },
      {
        "bodywt": 2.5,
        "name": "Rabbit",
        "sleep_total": 8.4
      },
      {
        "bodywt": 55.5,
        "name": "Sheep",
        "sleep_total": 3.8
      },
      {
        "bodywt": 52.2,
        "name": "Chimpanzee",
        "sleep_total": 9.7
      },
      {
        "bodywt": 162.564,
        "name": "Tiger",
        "sleep_total": 15.8
      },
      {
        "bodywt": 100,
        "name": "Jaguar",
        "sleep_total": 10.4
      },
      {
        "bodywt": 161.499,
        "name": "Lion",
        "sleep_total": 13.5
      },
      {
        "bodywt": 25.235,
        "name": "Baboon",
        "sleep_total": 9.4
      },
      {
        "bodywt": 0.55,
        "name": "Desert hedgehog",
        "sleep_total": 10.3
      },
      {
        "bodywt": 1.1,
        "name": "Potto",
        "sleep_total": 11
      },
      {
        "bodywt": 0.021,
        "name": "Deer mouse",
        "sleep_total": 11.5
      },
      {
        "bodywt": 1.62,
        "name": "Phalanger",
        "sleep_total": 13.7
      },
      {
        "bodywt": 86,
        "name": "Caspian seal",
        "sleep_total": 3.5
      },
      {
        "bodywt": 53.18,
        "name": "Common porpoise",
        "sleep_total": 5.6
      },
      {
        "bodywt": 1.1,
        "name": "Potoroo",
        "sleep_total": 11.1
      },
      {
        "bodywt": 60,
        "name": "Giant armadillo",
        "sleep_total": 18.1
      },
      {
        "bodywt": 3.6,
        "name": "Rock hyrax",
        "sleep_total": 5.4
      },
      {
        "bodywt": 0.32,
        "name": "Laboratory rat",
        "sleep_total": 13
      },
      {
        "bodywt": 0.044,
        "name": "African striped mouse",
        "sleep_total": 8.7
      },
      {
        "bodywt": 0.743,
        "name": "Squirrel monkey",
        "sleep_total": 9.6
      },
      {
        "bodywt": 0.075,
        "name": "Eastern american mole",
        "sleep_total": 8.4
      },
      {
        "bodywt": 0.148,
        "name": "Cotton rat",
        "sleep_total": 11.3
      },
      {
        "bodywt": 0.122,
        "name": "Mole rat",
        "sleep_total": 10.6
      },
      {
        "bodywt": 0.92,
        "name": "Arctic ground squirrel",
        "sleep_total": 16.6
      },
      {
        "bodywt": 0.101,
        "name": "Thirteen-lined ground squirrel",
        "sleep_total": 13.8
      },
      {
        "bodywt": 0.205,
        "name": "Golden-mantled ground squirrel",
        "sleep_total": 15.9
      },
      {
        "bodywt": 0.048,
        "name": "Musk shrew",
        "sleep_total": 12.8
      },
      {
        "bodywt": 86.25,
        "name": "Pig",
        "sleep_total": 9.1
      },
      {
        "bodywt": 4.5,
        "name": "Short-nosed echidna",
        "sleep_total": 8.6
      },
      {
        "bodywt": 0.112,
        "name": "Eastern american chipmunk",
        "sleep_total": 15.8
      },
      {
        "bodywt": 207.501,
        "name": "Brazilian tapir",
        "sleep_total": 4.4
      },
      {
        "bodywt": 0.9,
        "name": "Tenrec",
        "sleep_total": 15.6
      },
      {
        "bodywt": 0.104,
        "name": "Tree shrew",
        "sleep_total": 8.9
      },
      {
        "bodywt": 173.33,
        "name": "Bottle-nosed dolphin",
        "sleep_total": 5.2
      },
      {
        "bodywt": 2,
        "name": "Genet",
        "sleep_total": 6.3
      },
      {
        "bodywt": 3.38,
        "name": "Arctic fox",
        "sleep_total": 12.5
      },
      {
        "bodywt": 4.23,
        "name": "Red fox",
        "sleep_total": 9.8
      }
    ],
    "highlight": [
      "Little brown bat",
      "Giraffe",
      "African elephant",
      "Human"
    ],
    "label": "name",
    "logX": true,
    "note": "All 83 species in the mammal-sleep dataset (Savage & West 2007 via ggplot2 msleep). The fit statistics are in the dataset's allometry table.",
    "title": "Daily sleep vs body weight, 83 mammal species",
    "type": "dot",
    "unit": "h",
    "x": "bodywt",
    "xLabel": "Body weight (kg, log scale)",
    "y": "sleep_total",
    "yLabel": "Total sleep per day"
  },
  "dataset": "https://karelbusta.dev/data/sleep/datasets/mammal-sleep",
  "ranking": "https://karelbusta.dev/data/sleep/animals-that-sleep-the-most",
  "related": [
    "https://karelbusta.dev/data/sleep/wild-elephants-sleep-2-hours",
    "https://karelbusta.dev/data/sleep/frigatebirds-sleep-in-flight",
    "https://karelbusta.dev/data/sleep/hunter-gatherers-sleep-less"
  ]
}