In what amounts to perhaps the most unhurried act of animal predation ever caught on camera, researchers have filmed for the first time a giant tortoise slowly – ever so slowly – closing in for the kill.
This drawn-out encounter – between a lumbering, almost leisurely giant tortoise (Aldabrachelys gigantea) and its grounded bird prey – is gruesome to watch. But it's also entirely transfixing.
After all, we've never seen a tortoise 'hunt' anything before. Who knew these dawdling giants had it in them?
"I couldn't believe what I was seeing," says biologist Justin Gerlach from the University of Cambridge. "It was horrifying and amazing at the same time."
The footage, captured on Frégate Island in the Seychelles archipelago, shows a female giant tortoise slowly pursuing a flightless lesser noddy tern (Anous tenuirostris) chick.
In a new study describing the encounter – said to be the "first documented observation of a tortoise deliberately attacking and consuming another animal" – the researchers indicate the hunt lasted seven minutes in total, including a passage where the tortoise pursued the chick along the top of a log.
The video – captured by Anna Zora, deputy conservation and sustainability manager with the Frégate Island Foundation – lasts for only a fraction of that, but it's enough to unequivocally show a deliberate, calculated attack on the part of the tortoise.
"It was looking directly at the tern and walking purposefully toward it," says Gerlach. "This was very, very strange, and totally different from normal tortoise behavior."
While tortoises such as A. gigantea (aka the Aldabra giant tortoise) are primarily herbivorous, the researchers say there have been anecdotal reports of tortoises squashing crabs with their carapaces, or unfilmed reports of the primarily herbivorous animals eating birds or consuming carrion.
Nonetheless, prior studies have never surfaced any actual evidence of hunting.
"Previously it's always been impossible to tell if the tortoise had directly killed the animal, or if it had just happened to sit down on one and find it conveniently squashed dead," Gerlach says.
The new footage settles the question, and in harrowing fashion. Tortoises do hunt creatures, after all, make no mistake. It just takes them a while to close the deal, and the prey has to be a pretty easy catch.
What remains unknown is just how often this kind of thing occurs. According to the researchers, there are signs this might be a lot more common than we knew, at least among the tortoise population of Frégate Island.
"The direct approach to the chick on the log suggests that the tortoise had experience of being able to capture a chick in such a situation," the researchers write in their paper.
"This indicates that this type of interaction is not infrequent for this individual. The observation of other tortoises hunting and consuming birds suggests that this behavior has been adopted by several individuals."
The findings are reported in Current Biology.