Researchers on Frégate Island in the Seychelles have captured, for the first time, the moment when a Seychelles giant tortoise turned into a violent predator, pursuing, attacking and eating a tern chick.
All tortoises were previously thought to be vegetarian, with the exception of occasional cases of eating carrion opportunistically, or consuming bones or snail shells for calcium.
But since the “hunting tortoise” was recorded last summer, the researchers have said others in the area have been spotted engaging in similar behaviour.
Experts suggest this entirely new hunting behaviour is driven by the unusual combination of a tree-nesting tern colony and a resident giant tortoise population.
Large-scale habitat restoration on the private island, which is managed for ecotourism, has enabled seabirds to recolonise it, and there is a colony of 265,000 noddy terns. The ground beneath the trees the colony is nesting in is littered with fish, as well as chicks that have fallen from their nests.
The footage shows the tortoise approaching the young tern, which doesn’t appear to be aware of the danger it is in, and instead repeatedly approaches the tortoise which is plodding steadily towards it.
When the tern gets within striking distance, the tortoise snaps its mouth closed, and the blow appears to immediately kill the bird. The footage stops before the tortoise begins eating the bird.
“This is completely unexpected behaviour and has never been seen before in wild tortoises,” said Dr Justin Gerlach, director of studies at Peterhouse, Cambridge, and affiliated researcher at the University of Cambridge’s Museum of Zoology, who led the study.
“The giant tortoise pursued the tern chick along a log, finally killing the chick and eating it. It was a very slow encounter, with the tortoise moving at its normal, slow walking pace.”
He added: “The whole interaction took seven minutes and was quite horrifying.”
The tortoise’s attack was filmed by Anna Zora, conservation manager on Frégate Island and co-author of the study.
“When I saw the tortoise moving in a strange way, I sat and watched, and when I realised what it was doing I started filming,” she said.
The researchers said that in most places, potential prey were too fast or agile to be caught by giant tortoises.
But they suggested that the way the tortoise approached the chick on the log suggests this type of interaction “happens frequently”.
On the Galapagos and Seychelles islands, giant tortoises are the largest herbivores and eat up to 11 per cent of the vegetation. They also play an important role in dispersing seeds, breaking vegetation and eroding rocks.
“These days Frégate island’s combination of tree-nesting terns and giant tortoise populations is unusual, but our observation highlights that when ecosystems are restored, totally unexpected interactions between species may appear – things that probably happened commonly in the past but we’ve never seen before,” said Dr Gerlach.
The research, supported by Fregate Island Foundation, is published in the journal Current Biology.
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies