Over the course of eight months, the researchers noticed something unexpected.
While half of the parrots got a calcium boost by breaking apart seashells in their cages with their beaks, the other half used pebbles or date pits to grind and scrape the shells into powder, which they then licked straight from the tool.
"What's also particularly interesting is that we observed a lot of tool transfer, where one bird would actually approach group members and steal the tool directly from their beak, and then go on to use it on a shell," lead study author Megan Lambert, a doctoral student of psychology at the University of York, told Live Science.
This kind of tool transfer is even more rare than tool usage itself. It's not clear whether this means the birds are passing the skill on from one individual to another, or if it's something innate for some birds who just get grabby with the available tools.
"Without witnessing the first tool using event, it's difficult to know how this behavior started, but the social system of these birds, and the fact that they share tools, would certainly support a scenario where tool use was transmitted socially after observing one innovative individual," Lambert told Discovery News.
Lambert and her colleagues also hope to learn more about the motivation behind the calcium scraping — tool-aided or otherwise. It makes sense for a parrot to want to ingest some calcium, because bird bones don't store it up the way human skeletons do, and it's a necessary ingredient in healthy eggshells. But intriguingly, four of the five parrots who used tools to get their calcium supplements were male. Male birds shouldn't really care about getting calcium, let alone finding innovative ways to acquire it.
The answer may be as simple as puke. Loving, intimate, sensual puke. Males of the species are often observed engaging in "regurgitative feedings" with females before they mate. It's possible that they're swallowing calcium powder to shore up their sweetheart's reserves during the big event.
That would explain why the calcium scraping was more common in the weeks leading up to breeding season, at least according to the observations made in this study.
The parrots involved in this study were wild, meaning they were raised out in the natural world, but they were in captivity. Until someone is able to catch this behavior out in the wild, it's hard to say for whether it's actually common practice for the species. For now, all we know is that these parrots can use tools to make their own vitamins - and that gains them entry into a very elite club.