In the middle of the Crusades, a shared love of birds and science established a 15-year truce. We've now learned a parrot from a part of the world Europeans and Arabs didn't even know existed played a part in this remarkable story.

Contemporaries called The Holy Roman Emperor Frederick II “stupor mundi” or “the astonishment of the world”. His possession of a bird from Australia or nearby islands is one astonishing aspect that has only come to light seven centuries after his death.

Among Frederick's unusual features for the time were his religious skepticism and interest in the philosophy and science of Aristotle. When ordered to engage in crusades by the Pope, Frederick instead made a peace treaty with Sultan al-Malik Muhammad al-Kamil of Egypt, granting Frederick temporary rule of Jerusalem.

The treaty occurred in part because Frederick and al-Kamil both feared other enemies, including Mongol invaders, and were worried conflict over the Holy Land would weaken them. However, another factor was the pair's strong commonalities, both of them loving birds and being unusually interested in science for rulers of their day.

As part of their diplomacy, Frederick sent al-Kamil a rare white peacock, while the Sultan gave Frederick a “white parrot”. Until now, this parrot's identity has been a mystery, but newly examined drawings reveal it to be a yellow-crested cockatoo species, then only living in Australia's Cape York, New Guinea, and Indonesia east of the Wallace Line – places entirely unknown in Europe at the time.

Frederick so loved birds, he wrote a manuscript De Arte Venandi cum Avibus (The Art of Hunting with Birds). This describes his fascination with falconry and includes exceptionally life-like drawings of everything from ostriches to blackbirds, as well as his cockatoo.

In 2014, Dr Heather Dalton of the University of Melbourne identified a cockatoo in a 15th-century altarpiece, thought at the time to be the oldest European depiction of an Australian animal. Her discovery drew the attention of three scholars at the Finnish Institute in Rome, who were studying De Arte in the Vatican library.

They wondered if the white parrot that appears several times in the manuscript's text and margins revealed a related bird reaching Europe long before the Age of Exploration. Dalton knew De Arte's text referred to a white parrot, but lacked the images to identify the species.

Halton and the three scholars have now published a paper in Parergon examining the drawings and description in detail. Although the bird in question has sometimes been called an umbrella cockatoo, native to northeastern Indonesia, the authors argue the drawings are much more consistent with Cacatua sulphurea, the yellow or lesser sulphur-crested cockatoo. Despite the manuscript's title, the seed-eating bird would have been no use for hunting.

As the authors note, the discovery reveals the extent of trading networks between Southeast Asia and Europe before direct contact.

“Although our part of the world is still considered the very last to have been discovered, this Eurocentric view is increasingly being challenged,” Dalton said in a statement. “Small craft sailed between islands buying and selling fabrics, animal skins and live animals before making for ports in places such as Java, where they sold their wares to Chinese, Arab and Persian merchants.”

Dalton told IFLScience that cockatoos are known for their long lives in captivity, making them much more likely to survive the long journey than other Australian natives – although one intriguing image has been found suggesting a kangaroo survived a similar trip. The cockatoos' rarity, ability to talk, and strong bonding with humans would have made them so valuable that they were traded from one end of Eurasia to the other.