CAMBRIDGE, England — A “vegetarian” giant tortoise has been caught on camera hunting, attacking and devouring a seabird. The “completely unexpected behavior” is the first time a tortoise has been caught deliberately hunting prey in the wild.
All tortoises were previously thought to be vegetarian, although they have occasionally been spotted feeding on bones and snail shells for calcium. Researchers believe this behavior was driven by the large tree-nesting tern colony and the large neighborhood of 3,000 tortoises on Seychelles’ Frégate island.
Extensive habitat restoration on the island has enabled seabirds to recolonize, and there is a colony of 265,000 noddy terns. The ground under the colony is littered with dropped fish and chicks that have fallen from their nests.
In most places, potential prey are too fast or agile to be caught by giant tortoises. The researchers say 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 percent of the vegetation. They also play an important role in dispersing seeds, breaking vegetation and eroding rocks.
Anna Zora, conservation manager on Frégate Island, filmed the interaction. “When I saw the tortoise moving in a strange way I sat and watched, and when I realized what it was doing I started filming,” she recalls in a statement.
Adds Dr. Justin Gerlack, at the University of Cambridge’s Museum of Zoology: “This is completely unexpected behavior and has never been seen before in wild tortoises. 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.
“These days,” he continues, “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.”
The findings are published in the journal Current Biology.
Report by South West News Service writer Joe Morgan.