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Planet Earth

Worst-Case Scenario Survival Handbook for Tortoises

InkfishBy Elizabeth PrestonJune 16, 2015 6:18 PM

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How long could you survive as a tortoise? Sure, the basic rules are easy: Eat plants. Hide in your shell. Slow and steady wins the race. But a tortoise in danger has to make some quick decisions. Especially if it's been flipped onto its back, slow and steady isn't good enough. The tortoise's best strategy, in fact, depends on its age. Ana Golubović, a biologist at the University of Belgrade in Serbia, is interested in how the behavior of turtles and tortoises changes over their lifetimes. Baby tortoises are small and fairly soft. As they age, their shells harden and the reptiles grow—and grow, and grow. The older the tortoise, the bigger it is. (You can even estimate a tortoise's age by counting rings on its shell, like a tree trunk.) This means an adult tortoise can rely on its shell in ways that a younger one can't. Golubović notes that not only do juveniles have softer shells, but they get no protection from their parents, and they're bite-sized to some predators. So a young tortoise that gets attacked and flipped is more vulnerable than its better-armored elders are. To learn how tortoises of different ages respond to danger, Golubović performed an extremely simple experiment. She hiked through remote, hilly sites in Serbia and Macedonia. When she found a medium-sized reptile called a Hermann's tortoise (Testudo hermanni), she carried it to a flat spot and set it down on its back. To a tortoise, this is code red—it means a predator may be trying to make a meal of it. Golubović measured how much time passed before the animal stuck its head out of its shell. After that, how long did it wait before starting to flail its stumpy limbs around? And did it ever manage to flip itself back over? (If the animals couldn't right themselves in 10 minutes, she gave them a hand.) Of the 338 tortoises Golubović flipped, about 30 percent never righted themselves. Size had a lot to do with it. "Larger tortoises had a harder time to self-right," Golubović says. And since the animals grow throughout their lives, larger tortoises are older ones. Accordingly, tortoises changed their emergency strategies with age. The younger a tortoise was, the sooner it popped its head out to assess the situation. Younger tortoises also waited less time between sticking their heads out and starting to move. The oldest tortoises in the study—those age 26 and up—spent the most time waiting motionless inside their shells. It makes sense for a smaller, younger tortoise to take action right away. Its weak shell doesn't give it much protection. On the other hand, it makes sense for an old, lumbering tortoise to chill on its back for a while. Its shell is sturdy, so it can wait out a predator. But stretching out its limbs to right itself (which is sure to be a long project) would make it vulnerable. "Our understanding of how these strategies are shaped during the lifetime can help us protect tortoises more efficiently," Golubović says. For example, young turtles in a captive breeding program should be tested before they're released, to make sure they react the right way when a predator attacks. Speaking of tortoise behaviors, I asked Golubović about a video I saw recently of a tortoise seeming to help an upside-down companion. Is this something tortoises really do? "It is a real thing," she says. "I had the opportunity to see wild running Hermann's tortoises helping each other to stand up after falling on their backs on several occasions. Mostly I observed males helping females." Things aren't always so adorable, though. "It is even more common for tortoises to try to flip each other on their back," Golubović continues. During fights between males, for example—or "during mating when the female can push the male and flip him over." https://www.youtube.com/watch?v=xJ87DJl_jbc

Image: by Amanda (via Flickr)

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