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Turtles have been spotted performing underwater push-ups while hibernating 鈥� something that might help them grab enough oxygen to stay alive.

Mike Plummer from Harding University in Arkansas and his colleagues noticed the behaviour by chance while keeping about 25 smooth softshell turtles (Apalone mutica) in an outdoor simulated pond.

During regular check-ups while the turtles were hibernating, the researchers saw them regularly raise and lower the back part of their body in a push-up fashion over 1000 times. 鈥淲e were very surprised to see the behaviour,鈥� says Plummer. 鈥淣obody鈥檚 ever seen it, best I can tell.鈥�

The turtles typically spend the winter partially buried in sand or mud at the bottom of rivers or streams so are hard to observe in the wild. Although the reptiles can breathe in air, this species is well-known for its ability to obtain oxygen through the skin, which has a similar permeability to gases as amphibian skin. 鈥淲e hypothesised that the push-ups resulted in replenishing the water next to the turtle鈥檚 skin with oxygenated water,鈥� says Plummer.

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Further experiments in an aquarium seem to agree with their theory. The turtles did more push-ups in warmer water than colder water 鈥� warmer water carries less oxygen than cold water, so the turtles would have had to refresh their water more often in warmer conditions to get the oxygen they need.

But Plummer is cautious about drawing conclusions yet. It鈥檚 possible that the turtles did push-ups because they were kept in still water. 鈥淪ince the water wasn鈥檛 moving, that means that the oxygen in the water next to the body was being depleted,鈥� he says. In their natural habitat, water is constantly moving over their skin due to currents so they have a continuous supply of oxygen.

Whit Gibbons from the University of Georgia is impressed with the discovery, though, which suggests that turtles are able to adapt to oxygen levels in water. 鈥淜nowing how a widespread group such as softshell turtles respond to decreased oxygenation may have implications for water quality issues in some areas,鈥� he says.

Some amphibians are known to move parts of their body as a tactic to obtain extra oxygen. Aquatic hellbender salamanders, for example, rock back and forth to help with respiration through flaps on the sides of their body.

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