A team of scientists has released an astonishing video showing a Seychelles giant tortoise ( Aldabrachelys gigantea ) attacking and eating a tern ( Anous tenuirostris ) chick. It is the first document of deliberate hunting in any species of wild tortoise.
“The tortoise chased the tern chick along a log until it finally managed to kill and eat it,” explains Justin Gerlach, an affiliate researcher at the University of Cambridge Museum of Zoology, who led the study. “It was a very slow encounter, the turtle was moving at its usual pace. The whole interaction lasted seven minutes and it was quite distressing ”, confesses the researcher. The episode was filmed by Anna Zora, co-author of the study, which has been published in the journal Current Biology, and conservation manager on Frégate Island, Seychelles. It is a privately owned island managed for ecotourism and home to some 3,000 turtles.
Usual windbreakers?
Turtles were traditionally believed to be vegetarians, although they had been seen opportunistically feeding on carrion, and they have also been known to eat snail bones and shells to get the calcium they need. But never until now had any species of turtle been seen actively chasing its prey in the wild, and it was not known if this happened or the turtles took advantage of the remains of crushed or dead animals.
For the researchers, this strange behavior is due to an unusual combination of two populations of species that do not usually interact. For one thing, giant tortoises are the largest herbivores on the Galapagos and Seychelles, eating up to 11% of the vegetation. They also play an important role in seed dispersal, breaking down vegetation and eroding rocks. On the other, the extensive restoration of the island’s habitat has allowed its re-colonization by seabirds, and there is currently a colony of more than two hundred thousand terns. Because of this, dead fish and chicks fallen from their nests are easily found on the ground.
While potential turtle prey is typically too fast and agile to be seized, these stray chickens are easier to catch. The researchers explain that, since the terns nest in high places, the instinctive behavior of the chicks when falling consists, precisely, in avoiding the ground at all costs, and this is, probably, the reason why the animal remained in the trunk even as the tortoise approached him. A turtle that, in the opinion of the experts, knew very well what it was doing: “It seemed to me that this animal had hunted successfully before,” says Gerlach.
Now, if this turtle was indeed an experienced hunter, many questions remain: “Could we be seeing a population of tortoises that is developing a new type of behavior with evolutionary implications, or is it just a one-off observation of an unusual event? ? “
The scientist suspects that conservation efforts on the island could be, in part, what is causing the appearance of this unusual behavior. Although seabird and turtle populations have declined over the past hundreds of years, efforts on the island have increased the populations of both to create a unique combination of tern and giant tortoise populations. “We are recreating conditions for natural behaviors that people have not seen in hundreds of years,” concludes the researcher.
