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It's True: Crocodiles Are Able to Sleep With One Eye Open • Mirror Daily

(Mirror Daily, United States) – No matter how unbelievable it might sound, it’s true: crocodiles are able to sleep with one eye open, so they can stay on the lookout for both predators and prey.

A new study has come to confirm what was considered to be only a tale straight from the Australian legends; no reliable scientific evidence was found to either confirm or disprove this theory – that is, until now. According to researchers from the La Trobe University, Australia, crocodiles are indeed able to keep watch during sleep.

This amazing ability – that some of us might secretly covet – is called unihemispheric sleep; in other words, the crocodile can keep one half of the brain alert while the other one sleeps, a habit that requires one eye to stay open.

Some other species are able to engage in unihemispheric sleep, such as dolphins or birds, but research on this phenomenon occurring in crocodiles has been limited. Lead researcher Michael Kelly of the La Trobe’s School of Life Sciences has expressed his excitement over the findings, which are the first reliable ones to involve crocodilians.

Kelly was joined in his endeavor by co-authors Richard Peters and John Lesku of the same institution, and Ryan Tisdale, of Max Planck Institute for Ornithology, Germany. The group found these discoveries to be key in reviewing the way we look at the evolution of sleep.

With the help of infrared cameras installed in custom-made aquariums, the researchers were able to observe the sleeping habits and general behavior of young saltwater crocodiles day and night. According to the study, the crocodiles measured somewhere between 40 to 50 cm (16 to 20 inches) long.

Researchers noticed that when humans were present in the room with the aquarium, the crocodiles were very watchful, and if they wanted to sleep, they kept one eye open and focused on where they last saw the humans. The Max Planck Institute for Ornithology in Germany has also studied the phenomenon, and their findings are in agreement with this new study.

Crocodiles can also sleep with both eyes closed, but studying them in lab conditions with humans present caused them to be more likely to keep one eye open. Older specimens were also thought to keep one-eye watch for the younger ones, as a protective behavior from predators.

Researchers reached a very interesting conclusion about what we consider “normal sleep.” If some birds, reptiles and aquatic mammals can sleep unihemispherically, then our whole-brain sleep should be considered an evolutionary novelty.
Image Source: Dreamatico

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