It might be time to ditch the phrase “gentle giant.”
Researchers in the Seychelles have filmed a giant tortoise chasing and devouring a tern chick in one gulp. The scientists involved in the discovery say it is the first time such an act has been captured on camera. Even they are shaken up.
“It’s totally surprising and quite horrifying,” said Justin Gerlach, an island ecologist in Peterhouse, Cambridge, England. “The turtle deliberately chases this bird, kills it and then eats it. So yes, it is hunting.”
Giant tortoises, now found only in the Seychelles and the Galápagos Islands, were believed to be herbivorous. In fact, their vegetarian diet is thought to have shaped their ecosystems similar to elephants or bison. But in an article published Monday in the journal Current Biology, Dr. Gerlach and Anna Zora, a co-author with the Frégate Island Foundation, point out that there is evidence that the hefty reptiles may occasionally supplement their diet. Turtles sometimes consume snail shells and bones from dead birds, goats, and even other turtles. But hunting?
Turtles have been rumored to stalk seabird chicks, who become helpless after falling from their nests. But until the video was captured — revealing a scene a bit like PD Eastman’s “Are You My Mother?” if it had been written by Roald Dahl instead — Dr. Gerlach assumed that such an observation was a misunderstanding at best.
‘No one has looked for it, because why would you? Turtles don’t hunt,’ said Dr Gerlach. “You’re not just going to waste your time looking for a hunting turtle.”
Now he wonders what else we can learn from these creatures, which can live for over 200 years and grow to over 500 pounds.
“It’s quite a mystery they’ve uncovered here,” said James Gibbs, a herpetologist at the State University of New York and the Galápagos Conservancy who was not involved in the study.
When Dr. Gibbs watched the video, he was amazed at how slow and clumsy the attack is.
“It’s a very interesting combination of diligence and incompetence,” he said.
dr. Gibbs has studied the giant tortoises in the Galápagos for about 30 years, where he said that tortoises have developed a curious relationship with birds.
“The tortoises will get up and stretch out all their limbs and tail, and finches will come to rid them of ticks,” said Dr. Gibbs. ‘I’ve heard over the years that the turtles sometimes fall down and flatten the finches and eat them. But those were just anecdotes, and having spent many, many years there, I’ve never seen it myself.”
But there is no denying what is happening in the Seychelles video. Indeed, the scientists note that the turtle shows signs that it has previously preyed on seabird chicks.
For example, when turtles eat leaves, grass, or fruit, they stretch out their tongues and draw the food into their mouths. But the turtle in the video has retracted its tongue and closed its eyes — signs that it’s wary of some degree of danger with this food source.
“It behaves in a different way from normal feeding,” said Dr. Gerlach. “It’s not just collecting food. It is deadly to gather food.”
According to Dr. Gibbs, the fact that the giant tortoise is female may be an important clue to the shocking behavior. Island systems tend to lack calcium, an essential mineral for building eggshells.
So while the video of a giant tortoise attacking a helpless tern chick may be difficult for some people to see, predation may simply be one way the animals ensure the success of the next generation.
“We’re used to them not being particularly interesting, slow moving and probably pretty dumb,” said Dr. Gerlach on giant tortoises. “But there’s clearly so much more to these animals.”