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 is putting itself at some risk to do this; normally they avoid anthing near their eyes, but this one is ignoring the defensive pecks from the bird as it attacks.

Although this behaviour has only been caught on video this once, 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. It could be a rare behaviour which is interesting but not particularly significant. On the other hand, it could be widespread and important to the tortoises; we simply don't know. 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 plan to set up student projects to investigate this further. Research will try to establish 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?

    I hope to start sending students to look into this in 2022, which will be a fantastic opportunitiy 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