Nodding off is dangerous. Some animals have evolved extreme ways to sleep in precarious environments

Animals that navigate extreme conditions and environments have evolved to sleep in extreme ways. For a long time, scientists could only make educated guesses about when wild animals were sleeping. But in recent years, tiny trackers and helmets that measure brain waves have allowed researchers to glimpse for the first time the varied and sometimes spectacular ways that wild animals snooze. Scientists have observed that chinstrap penguins in Antarctica sleep for seconds at a time to guard newborns. Frigatebirds that soar for weeks at a time get their winks on the wing. Elephant seals spend time sleeping while diving.