Researchers were shocked to discover that the vegetarian reptiles have started hunting down prey.
Weighing in at up to 417kg and measuring up to 1.3 meters in length, giant tortoises have a reputation for appearing outwardly nonchalant - shambling along, munching on vegetation and seeming about as dangerous as their much smaller, domestic counterparts that have been kept as pets for centuries.
Now however, researchers studying Seychelles giant tortoises (Aldabrachelys gigantea) have made a shocking discovery that is likely to change how we perceive these 'gentle giant' reptiles.
During the summer of 2020, one of the tortoises was captured on camera attacking and then eating a tern chick on Fregate Island - a private luxury resort that is home to around 3,000 tortoises.
Other giant tortoises on the island have also been observed engaging in similar behavior.
"This is completely unexpected behavior and has never been seen before in wild tortoises," said Cambridge University's Dr. Justin Gerlach.
"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 - the whole interaction took seven minutes and was quite horrifying."
The discovery is quite remarkable because, until now at least, tortoises were all thought to be vegetarian, feasting only opportunistically on carrion and on bones and shells as a source of calcium.
It is the first time any tortoise species has ever been seen actively hunting and killing prey.
"These days Fregate 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.