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.
The video, which recently trended on Reddit, depicts a behavior that's just beginning to be understood.
"Many mammals show species-typical sleeping behaviour, such as dogs circling before lying down, lending support to the idea that sperm whales sleep during these drift dives," study author Dr. Patrick Miller, a professor of biology at the University of St. Andrews in Scotland, said in a written statement.
Evidence for this study came about a few years ago when Dr. Miller and his researchers found a pod of snoozing sperm whales at sea, off the coast of Northern Chile. As the whales floated motionless, with their noses at the surface of the water, they seemed unfazed by the approaching boat of researchers--that is, until the boat accidentally bumped into one of them. D'oh.
"Reduced responsiveness that reverses with sufficient stimulation to cause waking is another important criteria that allows us to consider this to be a sleeping behavior," Dr. Miller noted.
The study, which was published in Current Biology in 2008, serves as the first evidence that whales in the wild may sleep with both sides of the brain, Dr. Miller said. His research suggested that such whales are totally asleep for about 7.1 percent of their time at sea, most often between 6 p.m. and midnight.
The rhinoceros beetle (pictured) can push around 850 times its weight.
Largest Invertebrate (Land)
The coconut crab weighs about 6.6 pounds and its legs can span up to two and a half feet Liz Hall from the Melbourne Aquarium inspects Coconut Crab as he takes possesion of a coconut in Melbourne, 19 December 2006. They Coconut crab (also known as the Robber Crab) are the largest living crab in the world and can climb coconut trees to harvest coconuts which they can break with their huge nippers and have been gruesomely know to feed on injured or unconcious people in the bush. (William West, AFP / Getty Images)
The giant squid is the world's largest invertebrate, and the largest ever measured was 59 feet long. Giant squids also have the largest eyes of any animal, each one about the size of a human head.
The etruscan shrew is the smallest mammal (by weight) in the world. The smallest animal by skull size is the bumblebee bat.
Most Venomous Animal
The sea wasp jellyfish (pictured) has enough venom to kill 60 adult humans. Photo: <a href="http://www.flickr.com/people/65578066@N00" target="_hplink">Guido Gautsch/Flickr</a>
Arctic terns migrate about 11,000 miles to the Antarctic each year...and then come all the way back! An Arctic Tern dives down to protect its nest on June 24, 2011 on Inner Farne, England. (Dan Kitwood, Getty Images)
Blue whales' low-frequency pulses can be heard over 500 miles way. At 188 decibels, these sounds are louder than a jet engine. In this picture taken on March 26, 2009, shows a blue whale swimming in the deep waters off the southern Sri Lankan town of Mirissa. (Ishara S. Kodikara, AFP / Getty Images)
World's Most Extreme Animals
North African ostriches run up to 45 miles an hour, making them the fastest land bird. They are also the biggest, weighing up to 345 pounds. An african ostrich eats at the Addo National Elephant Park, north of Port Elizabeth, on June 24, 2010. South Africa is hosting the 2010 FIFA World Cup. (Patrick Hertzog, AFP / Getty Images)
Peregrine falcons dive toward their prey at over 200 mph. A young male Peregrine Falcon eats meat taken from the protective glove of Taronga Zoo bird trainer Erin Stone (unseen) following a short flying lesson in Sydney on December 9, 2009. (Greg Wood, AFP / Getty Images)
Sailfish can swim at speeds of up to 68 mph, although experts disagree as to just which species of sailfish is the fastest. Sailfish jumping out of the water on January 16, 2006 in the Florida Keys, Florida. (Ronald C. Modra, Sports Imagery / Getty Images)
Cheetahs can run at speeds up to 70 mph. Majani, a 2-year-old male African cheetah, exhibits lighting speed Friday, March 19, 2004 while chasing a mechanical rabbit at the San Diego Zoo's Wild Animal Park as part of the Park's environmental enrichment program. (Ken Bohn, San Diego Zoo / AP)
Three giant tortoises are estimated to have lived over 175 years, with one estimated at a whopping 255 years. Image: Harriet, who died in 2006, was thought to be the third longest-lived tortoise on record. <a href="http://www.flickr.com/photos/doctorow/123660557/" target="_hplink">Cory Doctorow/Creative Commons</a>
World's Most Extreme Animals
African elephants are the heaviest and second tallest land animals. Large males can exceed 13,000 pounds and are 12 feet tall at the shoulder. This photo made on February 10, 2011 shows an elephant in Tsavo west national park, some 350 kilometres southeast of Nairobi. (Tony Karumba, AFP / Getty Images)