They were filmed using pebbles for grinding, thought to be a uniquely human activity – one that allowed our civilisations to extract more nutrition from cereal-based foods.

Megan Lambert from the University of York, UK, and her colleagues were studying greater vasa parrots (Coracopsis vasa) in an aviary when they noticed some of the birds scraping shells in their enclosure with pebbles and date pips.

“We were surprised,” says Lambert. “Using tools [to grind] seashells is something never seen before in animals.”

Afterwards, the birds would lick the powder from the tool.

Some of the parrots even passed tools to each other, which is rarely seen in animals. This behaviour was exclusively male to female.

Lambert and her team, who watched the parrots for six months, noticed that the shell-scraping was more frequent before their breeding season.

Since seashells contain calcium, which is critical for females before egg-laying, they suspect that the parrots could be manufacturing their own calcium supplements, as the mineral is probably better absorbed in powder form.

Greater vasa parrots are native to Madagascar and have breeding and social systems unique among parrots. For example, two or more males have an exclusive sexual relationship with two or more females, and they are unusually tolerant of their group members. The reproductive ritual of sharing tools and grinding could be yet another one of their quirks.

But the purpose of the behaviour is not yet settled. Although females need the calcium, it was usually males who were caught grinding. Perhaps, they regurgitate the mineral and pass it on to their mate: they are known to do so with food.

But why use a tool and not just the beak, anyway? The team suspects that using their beak alone for grinding may be uncomfortable.

Lambert now hopes to follow up by observing parrots in the wild. “I would like to see if they interact with seashells before breeding season in nature as well,” she says.

Previously, their cockatoo relatives have been spotted using sticks to retrieve fallen objects and last year they were observed learning these skills from others.

Alex Kacelnik from the University of Oxford, one of the authors of the cockatoo study, is fascinated by the new discovery in parrots.

“It adds to the rich assortment of tool-related skills in a growing number of species,” he says. “It is hard to believe that until a few decades ago humans were supposed to be the only species that used tools.”

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