Why do sperm whales sleep vertically?

Popular photos have surfaced online showing sperm whales gathered together, seemingly motionless and arranged vertically in the water. The whales, which are roughly the size of school buses, almost always appear to be "standing" and clustered in pods of five or six. read more

For sperm whales, "drifting off to sleep" isn't just a figure of speech. The video above shows an odd habit in which some sperm whales in the wild slumber vertically for short periods of time, and perform slow rhythmic dives as they literally drift to a complete sleep. read more

The whales were found to spend seven percent of their day in these vertical sleeping positions near the surface of the water, where they napped from 10 to 15 minutes. Researchers suggested at the time that they might be one of the world's least sleep-dependent animals. read more