Greater vasa parrots have officially been granted membership in the exclusive club of animals that use tools, thanks to a recently published study that found they can do something never seen before in any animal species.

In the spring of 2013, psychologist Megan Lambert was doing routine observations of the birds at the Lincolnshire Wildlife Park when she noticed something rather extraordinary — some of the greater vasas were picking up pebbles or date pits in their beaks and using them to grind down the seashells that line the bottom of the aviary.

Some birds eat seashells, which are made on calcium carbonate, because they need the calcium to develop their egg shells. But it's the first time any species has been seen purposefully breaking down the shell before eating it.

"This is what's really interesting about the study," said Megan Lambert, a psychologist and doctoral candidate at the University of York in the UK. "We've never seen any other animals, aside from humans, actually using tools for grinding."

"They'll basically grind the pebble against the shell, and then that results in a bit of a powder," Lambert told CBC's Quirks & Quarks in an interview set to air Saturday at noon. "Then they'll lick that powder off of the pebble."

Lambert and her research team believe that by grinding the shells down, the parrots can process calcium more efficiently. Studies carried out with chickens have shown that smaller particles results in better retention of calcium.

There's little doubt that, in general, parrots are intelligent animals. Of the 300 parrot species, some can mimic human speech, while a handful of others are known to use rudimentary tools. But the drably coloured greater vasas, native to Madagascar and known for their sociability, playfulness and promiscuity, are unique in their ability to purposefully grind down seashells.

Interestingly, four of the five vasas at the wildlife centre that Lambert observed grinding shells were males. The behaviour was most frequent in the lead up to breeding season, which begins in April.

Lambert says researchers "really don't know" why the behaviour is so much more prominent in male vasas.

"But one of the ideas we have is that, during courtship and during the breeding season, the males will often feed the females, so it may be that the females actually prefer these males that are feeding them calcium-rich food."

It's still not known if greater vasas use tools this way in the wild, Lambert added. But the study, published in the journal Biology Letters last month, puts the greater vasa in the special company of tool-using birds like New Caledonian crows, Egyptian vultures and woodpecker finches.