A bird can sleep without landing

Electrodes carried by great frigatebirds over the ocean recorded something once inferred but not directly shown: the birds slept in flight. They sometimes rested one brain hemisphere at a time, especially while circling in rising air, and occasionally both. Yet their airborne sleep total was tiny compared with the long sleep recorded when they were back on land.

That finding does not mean every migrating bird routinely sleeps aloft, or that sleep is optional. It describes one species observed on multiday foraging flights around the Galápagos. The sharper lesson is that sleep can be reorganised under extreme ecological pressure. Frigatebirds do not abolish it; for a while, they compress it around the demands of staying airborne.