15 Amazing Facts About 15 Birds

A common raven looking pretty pleased with itself.
A common raven looking pretty pleased with itself. / Andreas Saatze-Stein/500px/Getty Images
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5. Some ducks sleep with one eye open.

A group of mallards resting on an icy lake.
A group of mallards resting on an icy lake. / Photo by Mike Kline (notkalvin)/Moment Open/Getty Images

When mallards nap in groups, the ones on the perimeter keep guard by sleeping with one eye open. While the others sleep more deeply, those on the outside of the circle also keep one side of their brain awake, even as they doze, so that predators won’t be able to sneak up on them.