{
  "type": "fact",
  "url": "https://karelbusta.dev/data/sleep/frigatebirds-sleep-in-flight",
  "title": "Frigatebirds sleep in mid-air, about 40 minutes a day",
  "claim": "Great frigatebirds on flights of up to 10 days over the ocean slept 2.89% of the time (0.69 h, about 41 minutes, per day), sometimes with both brain hemispheres asleep at once. Back on the nest, they slept 53.28% of the time.",
  "description": "EEG on flying great frigatebirds showed sleep in mid-flight, but only 0.69 h a day, mostly in seconds-long bursts at night.",
  "confidence": "single study",
  "published": "2026-10-14",
  "context": "This is the first direct evidence that birds sleep while flying. Frigatebirds can sleep with one hemisphere or with both at once, and both kinds of slow-wave sleep occurred on the wing. Asymmetric sleep made up a larger share in flight (71.57% of slow-wave sleep vs 47.64% on land), and the \"awake\" side was usually the one facing the direction of a circling turn. In flight, sleep came almost entirely at night, in episodes averaging about 11 seconds (longest 348 s), mostly while the birds circled upward on rising air. Caveats: this is one study of 14 birds, all breeding females from a single colony. The on-land recordings were made right after long flights, when recovery sleep is likely, so the 53% is not a normal day's sleep on land.",
  "sources": [
    {
      "authors": "Rattenborg NC, Voirin B, Cruz SM, Tisdale R, Dell'Omo G, Lipp H-P, Wikelski M, Vyssotski AL",
      "journal": "Nature Communications",
      "sampleSize": "15 breeding female great frigatebirds instrumented; EEG in flight from 14, on land from 9",
      "title": "Evidence that birds sleep in mid-flight",
      "url": "https://doi.org/10.1038/ncomms12468",
      "year": 2016
    }
  ],
  "method": "In August 2014, researchers on Genovesa Island in the Galápagos fitted breeding female great frigatebirds (Fregata minor) with head-mounted loggers. The loggers recorded EEG from both brain hemispheres and 3D head acceleration, and a separate GPS logger tracked position and altitude. The birds then flew foraging trips of up to 10 days and about 3,000 km over the Pacific. Sleep was scored in 4-second epochs as wake, slow-wave sleep or REM sleep. Each bout of slow-wave sleep was classed as bihemispheric (both halves asleep), asymmetric or unihemispheric (one half asleep) from the difference in slow-wave activity between hemispheres. Land comparisons use recordings averaging 16.4 h made after the birds returned to the nest.",
  "chart": {
    "data": [
      {
        "label": "In flight (n=14)",
        "value": 2.89
      },
      {
        "label": "On land after returning (n=9)",
        "value": 53.28
      }
    ],
    "highlight": [
      "In flight (n=14)"
    ],
    "note": "Results, \"Sleep loss in flight\", mean ± s.e.m. 2.89 ± 0.58% vs 53.28 ± 4.82%. The 0.69 h/day figure is stated in the abstract (2.89% of 24 h ≈ 0.69 h).",
    "title": "Share of time spent asleep, great frigatebirds",
    "type": "column",
    "unit": "%",
    "x": "label",
    "y": "value",
    "yLabel": "Time asleep (%)"
  },
  "dataset": null,
  "ranking": null,
  "related": [
    "https://karelbusta.dev/data/sleep/bigger-animals-sleep-less",
    "https://karelbusta.dev/data/sleep/wild-elephants-sleep-2-hours",
    "https://karelbusta.dev/data/sleep/hunter-gatherers-sleep-less"
  ]
}