❝ We already know that some birds can fly for weeks or even months at a time without landing, but this remarkable ability has raised a few questions about how, if at all, these creatures find the time to sleep. In the first study of its kind, scientists have monitored the brain activity of seabirds in flight and discovered that they regularly squeeze in some shut-eye while out searching for food, though how they perform on such little rest remains a little unclear.
❝ If there was ever a bird well-suited to sleeping on the job, it might be the frigatebird, a large seabird that scans the ocean surface for flying fish and squid. Recent research has shown that these elite gliders can stay aloft for months by hitching rides on clouds and are among the longest-flying creatures in the seabird world. But even frigatebirds need their sleep, so scientists have been perplexed as to how they maintain performance without regularly coming down for rest…
❝ To find some conclusive answers, an international team of scientists hooked up frigatebirds nesting on the Galápagos Island to a device to monitor electroencephalographic (EEG) activity and head movement during flight. This recorder was carted along for 10-day flights across 3,000 km (1,864 mi) with a GPS module on the bird’s back to monitor their position and altitude.
The data showed that during the day, the birds remained awake while searching for food, so business as usual. But when the sun went down and the birds soared, the awake EEG pattern changed to a slow-wave sleep pattern, sometimes for minutes at a time. This SWS often occurred in one half of the brain, but interestingly, sometimes in both hemispheres at the same time, suggesting that unihemispheric sleep isn’t critical to maintaining aerodynamic control.
❝ Compared to how frigatebirds sleep on land, however, the SWS sleep mode was more frequent. By tracking the head movements of the birds, the researchers found that as they circle on rising air currents while sleeping in this way, it allowed them to keep one eye open in the direction they were turning.
The big surprise was that the frigatebirds were only sleeping for 42 minutes per day — compared to the usual 12 hours a day on land. Working out comparisons with what we know about sleep and sleep deprivation in other species – like us – will be part of where these studies will be going next.