With their sharp teeth and powerful jaws, crocodiles have earned themselves the reputation of being one of the fiercest hunters in the animal kingdom.
This harsh and often violent way of life in the wild leaves little wonder as to why these giant reptiles would want to keep an eye out for potential predators themselves.
In a study featured in The Journal of Experimental Biology, scientists at the La Trobe University in Australia have discovered that crocodiles engage in an unusual sleeping behavior called unihemispheric sleep.
This sleep pattern often involves keeping one eye open during rest, which is neurologically connected to the part of the brain that remains watchful.
While there is still much to learn about this behavior known as unilateral eye closure (UEC), it is generally believed that it is used to keep alert for potential dangers in the wild.
La Trobe researcher John Lesku explained that this behavior can also be seen in marine mammals, such as killer whales and bottlenose dolphins. He said that these animals use this ability to keep track of each other's movement in the water.
Lesku offered several possible explanations why animals engage in unilateral eye closure.
"It is thought that [UEC] reflects a way of maintaining group cohesiveness in a highly social animal," Lesku said.
"It could also be that, in a fairly boring aquarium, they simply keep their open eye on the most interesting thing — each other."
Lesku also pointed out that further research is needed in order to observe this sleep behavior in animals in their natural habitats.
Strange Sleep Behaviors in Animals
Aside from crocodiles, dolphins and killer whales, other members of the animal kingdom also carry out unusual behaviors when they go to sleep.
Sea Otters (Enhydra lutris)
Sea otters are known to wrap their fur in seaweed in order to stay anchored and avoid drifting to other places when they sleep. They have also been observed to come together to form "otter rafts," with some animals holding paws, possibly to stay together.
Malachite Sunbird (Nectarinia famosa)
To keep themselves safe during their sleep, male malachite sunbirds often fluff up their brightly colored pectoral tufts to ward away any potential predators at night. This allows the birds to mislead other animals into perceiving their bright yellow tufts as eyes of a much larger beast.
Wahlberg's Epauletted Fruit Bats (Epomophorus wahlbergi)
Researchers have also observed unihemispheric sleep in a group of large bats in South Africa known as Wahlberg's epauletted fruit bats. They have found that a significant number of these animals keep one of their eyes open while hiding their closed eye under their wing.
According to the scientists, the bats may have evolved this behavior as a way to stay alert against their natural predators such as African crowned eagles and vervet monkeys.
Photo: Alexander Cahlenstein | Flickr