It is has long been held that crocodiles sleep with eye open in order to pounce upon their unwary prey. While some may dismiss this idea as a modern myth, it turns out a crocodile attack only requires half of their brain to be awake.
In a related report by the Inquisitr, a Florida alligator attack became especially horrifying when a woman’s arm was bitten off and then the gator continued to chase her through the water.
Another old expression is the idea that you should “sleep with eye open” if you are concerned about an attack, but in this case the way crocodiles sleep allows them to both detect threats and find their latest meal. Researchers at Australia’s La Trobe University and Germany’s Max Planck Institute for Ornithology say that some species of birds and mammals have an ability called unihemispheric sleep, which allows them to remain vigilant by snoozing with half of their brain while the other half is still ready for action. This means their eye movements are seemingly awake even as all other physical attributes suggest the animal is sleeping.
Dolphins, some seals, manatees, and walruses are among those animals tested for unihemispheric sleep using an EEG test, and these scans did indeed prove that half the brain wave activity shows some half-and-half attributes. But even if crocodiles sleep with one eye open, would you really want to try and test that theory out and risk a croc attack?
As such, crocodiles have never been studied directly for this type of brain behavior, making this new study fairly unique.
“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 the study’s lead researcher Michael Kelly, of La Trobe University, in a press release.
John Lesku, a research fellow at La Trobe University in Australia and one of the authors of the new study, says that unihemispheric sleep can be used for multiple purposes. The bottlenose dolphin and killer whales often use this ability to keep track of members of their own species, so it is not always about being wary of threats.
“It is thought that [UEC] reflects a way of maintaining group cohesiveness in a highly social animal. It could also be that, in a fairly boring aquarium, they simply keep their open eye on the most interesting thing – each other,” Lesku told Live Science.
In order to prove whether crocodiles sleep with one eye open, the researchers observed a young croc in 24 hour increments. They discovered that crocs will keep one eye open, but they also do not do it all the time.
“It certainly seems to me that the animals preferred to either have both eyes open or both eyes closed,” Lesku said.
The biggest exception is when a potential snack was within view of the crocodile’s nap time. If a human test subject stood opposite the crocodile, the croc was much more likely to keep one eye open in order to monitor the situation.
“The crocodiles focused their gaze towards the human, and, indeed, continued to watch the location [where] the human had been even after he left the room,” Lesku said.
Unfortunately, the scientists still need to confirm with an EEG that the crocodiles’ sleep patterns conform to the results from other species.
“The gold-standard for identifying sleep in mammals and birds is by looking at brain waves for specific patterns that indicate a sleeping or waking animal,” Lesku said. “In our study we focused only on eye state. Whether two closed eyes always means that the animal is asleep, and two open eyes for an awake animal is yet unknown.”
[Image via Futura Sciences]