Scientists captured the moment on video when a Seychelles giant tortoise — previously thought to be vegetarian — attacked and ate a tern chick in what they say is the first documentation of deliberate hunting in any wild tortoise species.
“This is completely unexpected behaviour and has never been seen before in wild tortoises,” Justin Gerlach, director of studies at Peterhouse, Cambridge and affiliated researcher at the University of Cambridge’s Museum of Zoology, said in a statement Monday.
“It was a very slow encounter, with the tortoise moving at its normal, slow walking pace — the whole interaction took seven minutes and was quite horrifying.”
Anna Zora, conservation manager on Frégate Island and co-author of the study, captured the ordeal, which took place on in July 2020.
“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,” said Zora in the statement.
Though tortoises are thought to be vegetarian, they have been spotted “opportunistically” eating carrion, as well as bones and snail shells for calcium.
Giant tortoises are the largest herbivores on the Galapagos and Seychelles islands, and eat up to 11% of the vegetation, researchers said.
Experts say that the new hunting behavior was caused by the “unusual” combination of a tree-nesting tern colony and a resident giant tortoise population on the Seychelles’ Frégate island, which is home to around 3,000 tortoises.
The way that the tortoise approached the bird also suggests this type of attack happens regularly, they said.
“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,” added Gerlach.