Crocodiles sleep with one eye open to keep watch for threats and prey, study finds

The open eye follows stimuli, including other crocodiles

The crocodiles were monitored with infrared cameras (GUILLAUME SOUVANT/AFP/Getty Images)

Crocodiles sleep with one eye open in order to scout their surroundings for threats or prey, a new study has found.

Researchers who used infrared cameras to examine the behaviour of juvenile saltwater crocodiles in an aquarium found that the predators use a technique called “unilateral eye closure”.

Past studies have shown that animals including birds, dolphins, seals and walruses also sleep using what is known as one brain hemisphere at a time, BBC News reported.

The practice enables animals to keep one half of their brain conscious and the corresponding eye open to scan the surrounding area.

The team at La Trobe University studied how the crocodiles reacted during sleep when approached by other young crocodiles as well as humans, and found that the animals followed stimuli with their open eye.

Dr John Lesku, who is behind the research published in the Journal of Experimental Biology, told The Telegraph that the study suggests that human sleep – where the brain shuts off – may be rare in the animal kingdom.

He said: “The value of the research is that we think of our own sleep as 'normal' - a behavioural shutdown that is a whole-brain affair.

“If ultimately crocodilians and other reptiles that have been observed with only one eye closed are likewise sleeping unihemispherically then our whole-brain sleep becomes the evolutionary oddity.”