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    "headline": "Frigatebirds sleep 42 minutes a day on ten-day ocean flights; a viral Short revives the half-brain sleep study",
    "description": "A YouTube Short on animals that sleep with one eye open points back to a Galápagos EEG study of 15 great frigatebirds; dolphins, mallards and fur seals share the trick, sea otters do not.",
    "datePublished": "2026-11-03T01:52:00+00:00",
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    "articleSection": "Science",
    "keywords": "dolphins, frigatebird, sleep science, Viral video, YouTube Shorts",
    "articleBody": "Great frigatebirds flying over the Pacific for up to ten days slept an average of just 0.69 hours a day, about 42 minutes, and did much of it with one half of the brain at a time. That figure comes from a 2016 study in Nature Communications led by Niels Rattenborg, and it is the science behind a YouTube Short from the creator @Informationfactt titled “5 Animals That Sleep in the STRANGEST Ways”, which has been circulating again this week. The trick the clip describes has a name: unihemispheric slow-wave sleep, or USWS. What the half-brain trick is In ordinary sleep both halves of the brain show the slow, high-amplitude brain waves of deep rest. In USWS, one hemisphere produces those waves while the other shows the fast, low-amplitude pattern of being awake. The eye wired to the awake side stays open. Researchers have recorded it in bottlenose dolphins, belugas, orcas, northern fur seals and a long list of birds, from mallards to peregrine falcons, according to a 2016 review by Gian Gastone Mascetti of the University of Padua, published in the journal Nature and Science of Sleep. For dolphins the payoff is breathing. They have to surface for air, and bottlenose dolphins have been shown to keep swimming and surfacing while half asleep. In one experiment pods of Pacific white-sided dolphins slept with the open eye facing inward, toward the rest of the group, apparently to hold formation. How the frigatebird study was done Rattenborg’s team fitted 15 breeding female great frigatebirds on Genovesa Island in the Galápagos with a 55-gram head-mounted EEG logger, an accelerometer and a GPS tag, then let them go. Fourteen came back after foraging trips of up to ten days and 3,000 kilometers. For nine birds the team also recorded sleep back on the nest, giving a direct comparison between sleeping in the air and sleeping on land. The recordings showed both kinds of sleep in flight: one hemisphere at a time, and both together. Sleep happened almost only at night, mostly while the birds circled upward on rising air, and the sleep bouts were short, about 11 seconds on average against 28 seconds on land. The birds even logged brief episodes that looked like REM sleep, with the head dropping and twitching. The detail that explains the “one eye open” idea is which side slept. When a bird circled left, the left hemisphere tended to show deeper sleep, meaning the right eye, facing into the turn, was the one most likely open. The authors read that as the birds watching where they were going. Why it matters Badiyaa ran the arithmetic the Short leaves out. On land the frigatebirds spent 53 percent of their time asleep, roughly 12.8 hours a day. In flight that fell to 2.89 percent, which works out to the 0.69 hours the paper reports, or about one nineteenth of their land total. The birds did not grow sleepier as the days passed, and once home their sleep intensity fell by about 3.9 percent per hour, the usual sign of a sleep debt being repaid. That overturns the comfortable assumption that long-distance flyers simply get a normal night’s rest on the wing. They do not. They run on a fraction of it and recover later, which the authors compare to the polygynous male pectoral sandpipers that sleep very little for three weeks while competing for mates in the Arctic summer. Ducks fit the same pattern on the ground. Mallards at either end of a sleeping row showed 150 percent more one-eyed sleep than birds in the middle, with the open eye pointed outward where a predator would come from, a behavior known as the group edge effect. Limits and what the clip gets wrong Only female frigatebirds carrying chicks were studied, and only during foraging trips, so the numbers may not hold for males, for migration or for other species. The spectral analysis of brain waves was based on the single night with the most sleep for each bird, and the authors say recordings spanning whole cycles of flight and nesting are still needed to show whether the lost sleep is fully repaid. The Short’s sea otter entry is the weakest. Sea otters do rest in groups called rafts of 10 to 100 animals and wrap themselves in kelp so they do not drift, and photographs of pairs sleeping paw in paw exist. But that is a behavior, not half-brain sleep; USWS has not been shown in otters. The clip is also a compilation of animal footage with voiceover, not original filming, so the images illustrate the claims rather than prove them. The firmest number remains the frigatebird’s: 42 minutes of sleep a day, taken in 11-second sips, somewhere between 130 and 160 meters above the Pacific. Further reading Rattenborg et al. 2016, Evidence that birds sleep in mid-flight (Nature Communications) Mascetti 2016, Unihemispheric sleep and asymmetrical sleep (PMC) Wikipedia: Unihemispheric slow-wave sleep Wikipedia: Sea otter Image: putneymark, CC BY-SA 2.0 via Wikimedia Commons This article was produced with AI assistance and reviewed by our Editorial Desk. How we work.",
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