Giant tortoises that hunt!

A chance observation led to a paper that has variously been described as: 'astonishing and fascinating', 'fascinating and terrifying at the same time', 'awesome', a 'fascinating paper', a 'horrifying (very cool) discovery', a 'very very cool discovery', 'horrifying and amazing', a 'tremendous bit of natural history observation', and an 'impressive paper' with 'one of the best paper titles I've seen in a while, and it's terrifying'.

In June 2020 a giant tortoise on Fregate island, Seychelles, was filmed hunting a tern chick, killing and then eating it. This behaviour was totally unexpected; tortoises are known to eat a bit of carrion given a chance but no-one ever thought they actively hunted and killed for food. The tortoise was putting itself at some risk to do this; normally they avoid anthing near their eyes, but this one was ignoring the defensive pecks from the bird as it attacks.

Although this was the first time the behaviour had been caught on video, it has been seen to be carried out by several different tortoises on the island. At present we do not know how many tortoises do it or how often. In 2022 two students from Peterhouse spent the summer studying the tortoises. They recorded several more hunts, which is starting to give us a picture of how significnat this behaviour is. We still don't know how widespread it is, or how important to the tortoises. Similarly, we don't know if this is a totally new behaviour that has developed or something that tortoises used to do hundreds of years ago, before humans disrupted island ecosystems and decimated the tern and tortoise populations. Restoration of islands like Fregate may also be restoring ancient species interactions, and so changing our preconceptions.

We are now planning for Peterhouse biology students with an interest in ecology to take the research furthers. We hope to answers to the following questions:

  • how many tortoises have learned to hunt? Fregate island, G Larose, STB
  • is it done equally by males and females, young and old?
  • how often do they do it?
  • what do they get out of it - is it significant or just a tasty snack?

    This is a fantastic opportunitiy for our students, enabling them to study some amazing biology on this expectional island. Fregate is biogeographically interesting, with several oddities in the Seychelles context. It was almost completely turned over to agriculture in the 1800s but somehow retained several species that are restricted to the island, most conspicuously the bizarre giant flightless tenebrionid beetle Pulposipes herculeanus. Since the 1990s it has become one of the most successful island restoration projects.

    This is an exceptionally exciting research opportunity and we look forward to finding out the answers soon.

    Links

  • Summary
  • Video abstract
  • The video
  • The full paper

    tortoise approaching the tern, A Zora

  • Contact

    Justin Gerlach by e-mail