Scientist in remote Chagos Islands says he saw crabs, previously thought to be scavengers, hunting and killing seabird.
A large, land-dwelling crustacean known as a coconut or robber crab has been seen hunting and killing a seabird, the first time such behaviour has been observed in the species.
The phenomenon was witnessed by a scientist, Mark Laidre of Dartmouth College, while he was studying the giant crabs in the remote Chagos Islands in the Indian Ocean.
The crab approached the bird and grabbed its wing in its claw, breaking the bone and causing the unfortunate booby to fall to the ground.
The crustacean then descended and approached the maimed bird, before breaking its other wing and sealing its fate. Within 20 minutes, and likely drawn to the scene by the smell of blood, another five crabs arrived and the motley crew of crustaceans began the grisly job of literally ripping the hapless booby to pieces. The event is described in the journal Frontiers in Ecology and the Environment.
The crabs are named after their penchant for coconuts, which they are able to crack open with their formidable claws. These snappy appendages can exert some serious force, as not only does its pinch beat that of all other crustaceans, but it is also more powerful than the bite of almost all other terrestrial animals, with only alligators outperforming them.
Even with this incredible power, which can reach up to 3,300 newtons of force, it was thought that the crabs were not actually active hunters, spending most of their time chowing down on the creamy flesh of coconuts while occasionally snacking on any carrion that they happen to come across on their beachy atolls.
Considering the wide distribution of the crabs, which live on little islands dotted across the Pacific and Indian Ocean, it is pretty incredible that this bird-hunting behavior has never been seen before. It could be that it is simply not that common, or it might be due to the fact that the Chagos Archipelago has not had permanent human settlements on it for some 50 years, meaning that this could actually be the crustacean’s natural behavior.
Regardless of how common it might be, it seems that it is enough to generate what is known as a “landscape of fear,” in which the distribution of the prey is influenced by that of the predator. Laidre found that if big coconut crabs were already living on an island then birds were less likely to be found living there too, and when birds were abundant on particular atolls, the crabs were unlikely to be so.
The British Journal Editors and Wire Services