When you get really sleepy, you may nod off(打瞌睡) for a short time. Chinstrap penguins(帽带企鹅) in the South Pole nod off more than 10,000 times a day!
A new study in Science said this. A group of scientists studied 14 chinstrap penguins in the South Pole. They put electrodes(电极) on the penguins' heads and necks to see their brain activities. The scientists also followed them by GPS and watched them for 10 days.
The penguins never have a long sleep-the longest sleep is 34 seconds. On average(平均), the penguins sleep 4 seconds at a time. But in one day, they sleep for more than 11 hours. So they get enough rest. The penguins sleep like this because they need to protect(保护) their eggs and babies. lf they sleep for too long, the babies may get hurt by seabirds and other penguins. Also, their home is usually noisy and crowded. So the parent penguins just have very short sleeps to stay alert. Dolphins sleep with only half a brain! Half of the brain is awake, while the other half falls into a deep sleep. They stay alert for 24 hours a day all their lives. Some birds also fly while sleeping with half of their brain. For example, frigate birds(军舰鸟) fly for months over the ocean. When the wind can keep them from falling into the water, they sleep for 10 seconds at a time while flying.