Animals & Sleep: Clockless Reindeer and Falling Seals

Research continues to show how sleep differs among animals.

One study published last month examined the daily, “circadian” rhythms of reindeer. Researchers from the U.K. and Norway found that its melatonin production is not controlled by a circadian clock.

“The molecular clockwork that normally drives cellular circadian rhythms is evidently weak or even absent in this species,” the authors concluded.

Melatonin is a hormone that is produced in the brain. It helps your body regulate the sleep/wake cycle.

An internal body clock helps control melatonin production. Natural daylight – and the lack of it at night – also helps drive this cycle.

But melatonin production in reindeer appears to be driven only by light and darkness. This has little effect on their sleep patterns, reports LiveScience.

Reindeer sleep after they eat. As ruminant animals, they tend to eat eight to 10 times a day.

Another recent study took a closer look at northern elephant seals. They never come out on land during long migrations of up to eight months at sea.

They almost constantly make repetitive, deep dives. And they rarely surface for more than a few minutes at a time. So when do they sleep?

A research team from Japan and the U.S. studied six juvenile seals. They measured body position and 3-D diving paths.

They found that the seals sank quickly to a depth that would be safer from predators. Then they rolled over and sank on their backs during slower “drift” dives. They wobbled in a way that resembled a falling leaf.

This drastically slowed their descent rate. As a result they had time to rest or process food.

The authors also suspect that the seals may sleep during the descent phase of these dives. A few seals that drifted in shallow areas even hit the seafloor without reacting, reports Natural History.

Read more about animals and sleep.

Image by Tristan Ferne