Tool-Using Parrots Use Pebbles to Grind Seashells

In the spring of 2013, Megan Lambert noticed the greater vasa parrots of Lincolnshire Wildlife Park doing something odd. They looked like they were licking the cockle shells that lined the floor of their outdoor enclosure. But when Lambert looked closer, she noticed that they were holding a pebble or date pit in their beaks, and rubbing these against the shells.

They were using tools.

Several birds can use tools. Woodpecker finches prise grubs from wood with twigs, New Caledonian crows do the same, Egyptian vultures drop rocks onto eggs to crack them open, and rooks can raise the water level of a pitcher by dropping stones into it, Aesop-style. But among the 300 species of parrot, tool use is relatively rare. Black palm cockatoos use rocks to drum on tree trunks, while hyacinth macaws use sticks to prise open nuts. The kea, a delightfully mischievous New Zealand parrot, can use and make tools in the lab, but no one knows if they do so naturally.

Thanks to Lambert’s observations, the greater vasa parrot joins this exclusive club. Native to Madagascar, the greater vasa is a bit of a goth parrot, eschewing the vibrant hues of its relatives in favour of black and dark grey plumage. They’re sociable and inquisitive, and will often explore and manipulate objects in captivity; while watching them, Lambert saw one thread a twig through the open links of a chain. That seemed like play. By contrast, the thing with the seashells was probably more purposeful.

Seashells are made of calcium carbonate, and birds need calcium to build the shells of their eggs. Lambert thinks that the vasas were using the pebbles and pits to grind down the cockles and liberate the calcium within them. Other egg-laying animals, including sandwich terns and gopher tortoises, have been seen eating seashells, presumably for the same reason. But the vasas are the only ones known to process the shells. “That’s particularly interesting because humans are the only other animals known to use tools for grinding,” says Lambert.

But if that’s the case, why is it that only male parrots ground the seashells? If they’re trying to get at calcium for egg-laying, surely the females should be at it? Possibly, but during courtship and sex, vasa males spend a lot of time feeding females with regurgitated meals. Perhaps the calcium content of those fluids is a signal of the male’s quality as a mate?

Regardless, the behaviour is certainly common. Over a few months, Lambert saw all ten of the park’s greater vasa parrots interacting with the seashells, and at least five of them grinding the shells with pebbles or pits. One particular bird, a male named JD, was an especially prolific tool-user.

He was also a prolific tool-donor. On 16 occasions, Lambert saw one of the female parrots nicking a tool from another—usually JD, who tolerated the “theft”. “It’s quite unique that tools are transferred directly between birds, as this is not commonly observed in the animal kingdom and may provide clues as to how this behaviour came about in the first place,” says Lambert.

So far, Lambert and her colleagues haven’t done any experiments with the parrots, which leaves a lot of unanswered questions. Do the birds learn to use the tools themselves, or do they pick it up from their peers? What’s the purpose of the behaviour, and does it actually influence the birds’ reproductive success? Do the parrots grind seashells, or use other tools, in the wild? And what else are these animals capable of?