Study Finds Crocodiles Can Sleep With One Eye Open

Posted on October 22, 2015

Crocodile photo

A new study has found that crocodiles sleep with one eye open. They may be partaking in unihemispheric sleep by sleeping with half of their brain at a time like some birds and aquatic mammals.

The behavior would enable crocodiles to immediately respond to threats or locate potential prey while half asleep. The research was conducted by Michael Kelly, Richard Peters and John Lesku from La Trobe's School of Life Sciences in Australia and Ryan Tisdale from Max Planck Institute for Ornithology, Avian Sleep Group, Germany.

The researchers found that the crocodiles were more inclined to sleep with one eye open when humans were present. The open eye was always focused on the human.

The researchers say the findings could indicate that our type of sleep using both hemispheres of the brain (bihemispheric) may be less common and more unique.

Michael Kelly, the lead author of the study, says in a statement, "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. What we think of as 'normal' sleep may be more novel than we think."

Dr. Lesku adds, "The value of the research is that we think of our own sleep as 'normal' - a behavioural shutdown that is a whole-brain affair. 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."

A research paper on the findings was published in the The Journal of Experimental Biology.

Photo: Michael Kelly/La Trobe