New research suggests the saying "sleep with one eye open" might be taken literally by crocodiles.
The recent study demonstrates crocodiles have the ability to sleep with only half of their brain at one time in a phenomenon known as unihemispheric sleep, La Trobe University reported.
The fascinating process likely allows crocodiles to keep one eye open and connected to the open brain while the other eye remains closed and attached to the sleeping brain, keeping them alert for predators and prey. This type of behavior has been observed before in some birds and aquatic mammals such as dolphins, but rarely in crocodiles. Observations revealed crocodiles were more likely to sleep with one eye open when humans were present, and tended to keep this eye trained on the potential threat.
"These findings are really exciting as they are the first of their kind involving crocodilians and may change the way we consider the evolution of sleep," said lead researcher Michael Kelly.
The findings could provide key insights into what makes for effective sleep in all kinds of creatures.
"The value of the research is that we think of our own sleep as 'normal' - a [behavioral] shutdown that is a whole-brain affair," said John Lesku from La Trobe's School of Life Sciences. "And yet, some birds and aquatic mammals sleep unihemispherically with one eye open. If ultimately crocodilians and other reptiles that have been observed with only one eye closed are likewise sleeping unihemispherically then our whole-brain (or bihemispheric) sleep becomes the evolutionary oddity."
The findings were published in a recent edition of the Journal of Experimental Biology.
