It is known that some animals are able to sleep with only one eye closed. A recent study reported on at CapitalOTC.com showed that crocodiles may well be among their number.
Why Do Some Animals Sleep With One Eye Open?
Aquatic mammals like whales, dolphins, and orcas are known to sleep with half of their brain at a time. This results in them having one eye open and one eye closed as the active hemispheres of the brain affect their eyes. The reason why these animals have to do this is that they breathe air but live underwater at all times, so they need to remember to surface at least once every 30 minutes to take a breath, either through their blowholes or their mouths.
This is not the only unusual sleep behavior observed in animals that live underwater. Sharks, who do not breathe air and are not mammals, have to keep water moving constantly over their gills to take in oxygen, and this means that they have to be in a constant state of swimming or moving. As a result of this, in order to breathe but never truly be asleep, sharks have their own special way of sleeping that rests parts of the brain at different times.
The Observations Of Crocodile Sleep Patterns
The crocodiles involved in the study we watched over periods of 24 hours to see how much time they spent with either both eyes open, both eyes closed, or one eye open and one eye closed. The crocodiles were seen to keep one eye open and one eye closed for just one hour a day. However, what is interesting is that when the crocodiles were shown something visually stimulating. For instance, if another crocodile was in the next enclosure to them, giving them something to watch or keep an eye on, the amount of time they spent with one eye open increased dramatically. This suggests that the crocodiles are capable of sleeping with one eye open, however, they only do this when they feel that they need to look out for predators or other crocodiles they might want to interact with.
Visual Stimuli Key To Whether Animals Keep An Eye Open
This is in line with other studies that have been done on dolphins, which showed that while dolphins are known to be capable of sleeping with one eye open at any time, they choose to do so more often when there are other dolphins in the vicinity. These observations were largely made in captivity, so it could well be that the dolphins would normally be on the lookout for predators when they sleep with one eye open, or simply looking around at their surroundings. Dolphins in captivity are, of course, aware that there is nothing likely to attack them, but there are also fewer interesting natural things for them to see.
Further studies will be required to see exactly how crocodiles sleep patterns do work, but it is interesting to see how animals capable of sleeping with half of their brain still focused and one eye still receiving information respond to different environments and stimuli.