It’s no secret that parrots are smart. Aside from mimicking human speech, they display some impressive problem-solving abilities. But unlike other brainy birds such as crows, they’re not regular tool users. Out of 300-plus parrot species, only a handful have been known to use tools (and even some of those have only showed that skill in lab settings).

Now, a new study suggests that the greater vasa parrot (Coracopsis vasa) can be added to that short list. At a wildlife park in the UK, researchers discovered that a group of these birds were regularly using seashells and other objects to improvise a sort of mortar and pestle. These are the first observations of a nonhuman using grinding tools.

Psychologist Megan Lambert and her colleagues were at the Lincolnshire Wildlife Park studying the parrots’ behavior when they noticed the birds paid a lot of attention to the seashells scattered around the floor of their enclosure. When they got a closer look, they saw that some of the parrots were grinding pebbles against the shells to create a powder, which they then ate. The birds put the pits from dates their keepers fed them to the same use.

The researchers saw five of the park’s 10 parrots doing this, and also found that they shared their tools with each other. Two of the male parrots let a female borrow their pebbles and pits and, in one case, actively offered them to her. Transfers like this are rare among tool-using animals.

Lambert and her team kept track of the parrots’ tool use from March to October 2013, and found that it peaked in the spring, with the birds taking up their makeshift grinders as often as twice an hour in early April, and dropped off later in the year. The parrots’ seasonal use of the tools may be because they breed in March and April, and need the powder from the calcium-rich seashells to produce their eggs.

“While other species are known to ingest seashells as calcium supplements, this birds’ method for doing so appears to be entirely unique,” the researchers write in their paper. If shell grinding is a way to get a nutritional boost for egg laying, then it’s odd that four out of the five tool users were male. Lambert suspects that this has to do with a quirk of the parrots’ social lives. During courtship and mating, male vasa parrots feed their female partners by regurgitating food into their mouths, in which case the females would benefit indirectly from the males’ grinding.

The researchers admit that they have more questions than answers after this initial observation. First, why would the parrots complicate things by using a tool to grind the shells instead their beaks? It’s possible that scraping the shells with their beaks is simply uncomfortable for the birds, or they might be able absorb more calcium from the fine shell powder than they do from larger chunks or flakes of shell.

The team also wants to do more work to figure out if vasa parrots use their grinding tools in the wild, or if the behavior is unique to the captive group at Lincolnshire and arose because they don’t have to worry about predators or finding food and have a lot of time on their hands (or wings). Still other experiments are needed to see if these parrots innately know how to use the tools, or picked the skill up from a member of the group who first figured it out through trial and error.

For now, tool use is another feather in the cap of an already interesting bird. Vasas, which are native to Madagascar, are curious, playful, and more sociable than most parrots. During their study, the researchers watched as one bird threaded a twig through the links of a chain. Toying with objects like this, the team says, could be a precursor to more advanced problem solving and tool use.