We like to think of tortoises as herbivorous gentle giants. Indeed, most people (myself included) assume that their behaviours are simple because of their slow moving lives, . Now new work is revealing that at least some tortoises hunt and eat baby birds.
Tastes like chicken…
Those who study tortoises full time know that these reptiles are not strictly vegetarian. One species of semi-aquatic tortoise was spotted a number of years ago eating frogs in captivity. Several wild tortoise species have also been seen consuming bones and snail shells which many experts assume is done to increase their calcium intake. There have even been a few anecdotal reports of Galapagos giant tortoises squashing birds under the weight of their heavy shells but nobody has been sure whether this squashing accidental or deliberate.
The new work published in Current Biology is revealing (in video format no less) the deliberate hunting of a tern chick by a female tortoise in the Seychelles. In the video the tortoise walks directly towards the tern and reaches out with her mouth open when the chick is in reach. The chick , being no dummy, recognises an attack when it sees one and runs up a log to get away from the reptilian menace. The tortoise pursues while continuing to bite at the bird. The chick tries to defend itself by pecking at the tortoise and fluttering its wings but it is all to no avail. The relentless tortoise carries on attacking, driving the chick further and further along the log. At the end of the log the flightless chick is too high off the ground to jump off and gets pinned at a dead end. Sensing that she finally has her quarry cornered, the tortoise closes her jaws directly on its head killing it. The chick drops and the tortoise eats it.
This whole encounter was a long one (to be expected from an animal known for moving slowly). From first approach to the death of the chick, the interaction is seven minutes in length.
What is particularly notable here is that during the attack the tortoise approached the chick with its jaws wide open and the tongue retracted. Apparently, this is typical of aggressive tortoise behaviour and is in contrast to their normal feeding where the tongue is stuck out. The direct approach to the chick on the log also hints that the tortoise had experience at being able to capture a chick in such a situation by cornering it well above ground-level.
While this is the first documented incidence of a wild tortoise hunting, killing and eating a bird, the team have had their suspicions that this was going on as they had occasionally seen a few tortoises in the areas nibbling on bird carrion and observed what they thought looked like bird hunting behaviour. Now they are certain that at least this population of tortoises has turned omnivorous. Why this has happened and whether it is more widespread remain unclear. This just published in Current Biology and my article on it will be published in The Economist shortly.