Dolphins

• Sleeping habit: with one eye open

Did you know that dolphins can’t sleep with their eyes closed or lying down? The explanation is that most marine mammals have to pay attention to predators and voluntarily breathe oxygen to live otherwise they will drown. In this case, dolphins are warm blooded creatures that need to keep moving to maintain a regular body temperature, so they have to sleep with one eye open to keep a part of the brain conscious. 

To be more specific, to prevent suffocation or drowning, dolphins allow one half of their brains to sleep at a time and the other half remains active to enable the dolphin to breathe and see the predators. For example, they close the left eye when the left half of the brain needs to rest and vice versa.  

This sleeping process can be found not only in cetaceans, but also in migratory birds. Some people have recorded dolphins swimming in circles and this was probably the explanation. This sleeping habit is also known as ‘unihemispheric sleep’ because only one brain hemisphere needs to sleep at a time and they alternate them periodically. 

Newborn orcas

• Sleeping habit: they don’t sleep

According to animal experts, newborn orcas and other baby cetaceans can’t sleep in the first month after birth. Although adult orcas can usually sleep for up to 8 hours when they are babies and new mothers they won’t sleep at all. 

New mothers can’t sleep because they have to protect their babies and need to be conscious to see them. Newborn orcas don’t have the muscle strength to sustain themselves and don’t have the necessary blubber to survive alone in the cold waters of the ocean, so they can’t sleep, as it’s important to keep up with their mothers who protect their path.

That being said, to stay alive, newborn orcas have to stay in their mother’s slipstream and they generate it while they keep moving… so during this process, they can’t sleep as well. 

As I said before with dolphins, orcas are actually cetaceans and cetaceans will usually activate the unihemispheric sleep process to rest properly, but researchers believe that new orca mothers don’t do this because they have never been observed with an eye closed. Thus, they literally can’t sleep in the first month after giving birth.