Tortoises are widely regarded as vegetarian creatures who eat grass. However, in the Seychelles, an Aldabra giant tortoise which was caught on video catching and killing a bird has stunned scientists. It has been described as the first time this behavior has been documented.
The scientists, led by Dr Justin Gerlach, Director of Studies at Peterhouse, Cambridge have researched the slow-speed hunt. The study has been published in the scientific journal Current Biology.
“Everybody knows, or everybody thought they knew, that tortoises are vegetarians,” he says. “Pretty much any herbivorous animal will eat a bit of meat that they come across. It’s a bit of free protein. So why wouldn’t they do so? But that’s just feeding on a bit of carrion. It’s not hunting. It’s not killing prey. And so this is totally unexpected.”
Footage of the tortoise hunting down a tern chick, showed that the prey fell from a nest in the trees to the location of the tortoise. The tortoise, sensing a meal, displayed the skills of an experienced predator and slowly creeped towards the chick before killing it.
“So it seems to be an aggressive action and it seems to be deliberate. There’s nothing very casual about this. So that all adds up to a tortoise that’s done this before,” Gerlach added, praising the skill of the tortoise.
The footage was captured on Fregate Island, a luxury resort in Seychelles by the conservation manager Anna Zora, who said the footage was a stroke of luck as she was with two volunteers.
“I said, guys, ‘look at this tortoise, it’s doing something strange,” she says. “It is only when something is strange enough out of the normality that your eyes pick it up. And that’s, I think, exactly what happened.”
Despite working in the Frestage Island that has over 3,000 Aldabra giant tortoises, Zora said it was the first time she would witness such a scene. She and the visitors had to fight off their instinct to save the chick.
“I remember one of the guys saying to me, ‘oh no! We need to save the chick’ and I stopped him, I said, look, if you were in the Savannah with a lion running after a gazelle, would you go and save the gazelle?” Zora says. “It’s a little bit the same concept. Nature can be cruel.”
Gerlach however proposed that the tortoise must have been hunting for chicks but it was only firstly recorded because sea birds, like the noddy tern, have recolonized the Fregate Island since work was done on the island to regenerate natural habitats.
“That was probably something that occurred much more commonly in the distant past, when there would have been many islands with tortoises and with seabirds, but over hundreds of years, humans wiped out both the sea birds and tortoises,” he says.
“It’s only the restoration work that’s been done on places like Fregate that has allowed the habitats to recover and the populations to recover. I suspect what we’re seeing is something that used to occur in the past, but no human has seen for 200 years.”