Bob Duchesne | BDN
Mallards are notorious for their ability to sleep with one eye open.
By Bob Duchesne, Special to the BDN • February 16, 2018 6:00 am
Winter is a dangerous time for me. I have too much free time to ponder imponderable questions, like “Do birds sleep?” Well, yes, but not the same way we do, and each species has its own way of sleeping.
Sleeping is dangerous. Slumber too deeply, and you may become somebody’s unwary lunch. Most small birds grab a few winks as needed, but they are hard-wired to wake instantly if disturbed by a neighbor, strange sound, or approaching threat. Awake, gone.
Some birds can sleep with one eye open, resting half of their brain while the other half remains alert. It’s called unihemispheric slow-wave sleep. The ability is not limited to birds. Certain whales and porpoises have demonstrated the knack, too. It’s most common in species that sleep in open fields or water, like ducks and seabirds.
Some long-distance migrants are capable of sleeping on the wing, since they often need to stay aloft for days or weeks at a time. But are they really sleeping up there? The only way to know is to wire them up and measure brainwave activity. Obviously, that is impractical for tiny birds.
Frigatebirds are large birds of the tropical oceans. They resemble prehistoric pterodactyls, with short legs and very long, pointed wings that allow them to stay aloft for days. These birds are large enough to be fitted with brainwave monitoring devices. Though they can rest briefly on water, they are not comfortable there. With such long wings, frigatebirds face difficulties taking off from a flat surface, and their tiny feet give them no boost.