Scientists find a medieval sandal and other unexpected artifacts in vulture nests in Spain

The bearded vulture, a large bird of prey with an unusual diet consisting primarily of bones, has long fascinated ornithologists. But now, a new study has shown why the bone-eating birds could be even more intriguing than once thought. Their carefully crafted nests, serving multiple generations, may also act as “natural museums,” preserving centuries-old cultural artifacts, according to scientists.

In Spain, researchers studied a dozen bearded vulture nests between 2008 and 2014. The team analyzed them layer by layer, uncovering over 200 human-made objects that the birds may have repurposed as building materials. Carbon dating of these items revealed that the nests date back to at least the 13th century, with the oldest artifact being a sandal that’s over 700 years old. The findings were published September 11 in the journal Ecology.

“We knew that the bearded vulture is a transporting species that can carry objects to its nest for construction, but we were surprised by the number of objects found and their age,” said lead author Antoni Margalida, an ecologist at the Pyrenean Institute of Ecology at the Spanish National Research Council in Jaca, Spain. “This means that these sites, used for centuries, are quality locations that different generations have used for breeding.”

Not only does the research open new avenues for finding cultural artifacts, but it could also help future conservation efforts for the species, the scientists said.

Artifacts in vulture nests

The bearded vulture is the only known vertebrate to specialize in eating bones, comprising up to 90% of the creature’s diet. As the study authors set out to find historical nests — sites no longer in use either due to local extinction or unsuitable habitat factors — they were primarily interested in finding bone remains. The team aimed to study the past inhabitants’ diet and compare it with the diet of modern birds today.

But the researchers said stumbling upon the copious number of artifacts entangled in the historical nests took them by surprise. Over 9% of the specimens pulled from the structures were human-made.

Besides the sandal, which was crafted from woven twigs and grasses, other items found within the nests included a painted piece of medieval leather that resembles a mask, remnants of a basket dated to the 18th century, an arrow from a crossbow, ropes and rigging for horses, and more. The sandal is the oldest artifact so far, but the study team has yet to carbon-date other items, Margalida said.

The documented findings offer an intriguing look into human culture, according to Margalida. “This can give us information about how people dressed, how they hunted (through the slingshots and crossbows found), and which domestic and wild species were most abundant in the ecosystem,” he said.

Because bearded vultures, which have a nearly 10-foot (3-meter) wingspan, like to nest in cliff caves or rocky areas that have stable temperatures and humidity, bone remains, human-made objects and other nest materials can stay relatively well-preserved, according to the research.

“This study sheds new light, and really a whole new angle on the place of the Bearded Vulture in our understanding of the interplay between a fascinating bird and the history of human culture,” John Fitzpatrick, director emeritus for the Cornell Lab of Ornithology, said in an email.

“The fact that Bearded Vultures are now recognized as ‘recording artists’ documenting human history just adds to their unique mystique,” he added. Fitzpatrick, who is also professor emeritus of ecology and evolutionary biology at Cornell University, was not involved with the new research.

In southern Spain, where the researchers recovered the nests, bearded vultures have been locally extinct for 70 to 130 years, according to the study. To find the nest sites, the study authors spent years looking into historical records as well as speaking with older residents of the area who remember the birds when they were around. Today, bearded vultures can still be found in areas of Europe, Asia and Africa, but they are less common and widespread than they once were centuries ago.

“While this research occurred in Spain, the Bearded Vulture has a broad distribution over the Old World — including in the Himalayas, the Caucasus, and the Ethiopian highlands,” said Evan Buechley, a researcher on raptor ecology and vice president of conservation for international programs with The Peregrine Fund, a nonprofit that aims to conserve birds of prey worldwide.

Studying other nests, such as those in Ethiopia or Tibet, “could reveal fascinating insights into the human histories of other mountainous regions of the world,” he added in an email. Buechley was also not involved with the study.

Saving the bearded vulture

The International Union for the Conservation of Nature Red List categorized the bearded vulture in 2014 as near threatened. By studying the birds’ nests, including those that are no longer in use, researchers can better understand factors that make habitats suitable, such as the basis of their diet or the effects of pesticides in the area, Margalida said.

In addition, understanding the species’ historical factors, such as their breeding distribution and diet, could help researchers decide where and how to reintroduce the species in future projects, Buechley said.

The research also highlights the large effect humans have on wildlife. Buechley pointed to the California condor. This New World vulture is a critically endangered species that faces issues with its chicks ingesting trash brought back to the nests by their parents.

“This underscores the importance of maintaining vast areas of wild habitat that remain largely free of some of the worst toxins that humans create and leave around the landscape for curious critters — even as big and rock-solid as Bearded Vultures — to play with and take home,” Fitzpatrick said.

“Bearded Vulture is already a revered bird bearing a special place in the hearts and minds of people who know about it,” he added. “Anything that informs the public about the fascinating ways in which wild birds and human culture intersect has huge value, both for our own appreciation of the extraordinary world around us and for our commitment to ensure the long-term protection of wild species and wild places.”

Taylor Nicioli is a freelance journalist based in New York.

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