Archaeologists in southern Spain have discovered over 200 human-made artifacts inside centuries-old bearded vulture nests, revealing how these birds inadvertently preserved traces of medieval life. The results, published in Ecology, are based on 12 abandoned cliffside nests previously occupied by the bone-eating raptor Gypaetus barbatus, which disappeared from the area around a century ago.
The most striking find was a woven esparto sandal dating back between 650 and 750 years ago. Credit: A. Margalida et al., Ecology (2025)
Between 2008 and 2014, researchers rappelled down cliffs in Andalusia to examine the nests, which had lain untouched since the vultures disappeared. Bearded vultures are unusual birds—they feed on bones almost exclusively, stain their feathers orange with mud, and return to the same nesting sites for generations. This habit created thick, layered structures of branches, wool, and bones that protected everything the birds brought home.
In these layers, the team encountered an extraordinary mix of natural and human-made materials. Most of the contents consisted of animal remains—more than 2,100 bones, 86 hooves, and dozens of eggshells—and approximately nine percent were human-made artifacts. Among them were 72 items of leather, 129 fabric fragments, 25 items made of esparto grᴀss, and a couple of tools, including a crossbow bolt and a slingsH๏τ.
The most striking find was a woven esparto sandal dating back between 650 and 750 years ago. Esparto, a tough Mediterranean grᴀss that is still used today to make baskets and espadrilles, was common in medieval footwear. The dry, cool conditions of the cliff caves preserved the shoe in nearly perfect condition. The same nest contained a fragment of painted sheep leather with red ochre paint, which was also several centuries old.
A collection of handcrafted materials found in ancient Bearded Vulture nests. PH๏τographs: Sergio Couto (A, B, D, and F) and Lucía Agudo Pérez (C and E). Credit: A. Margalida et al., Ecology (2025)
The objects were collected by the birds while they scavenged materials to build or repair their nests, sometimes gathering objects that had been discarded by nearby human settlements. As time pᴀssed, the nests became natural vaults, and fragile organic materials lasted much longer than they would have in the open air. The artifacts ranged from about 150 to 675 years old according to radiocarbon dating.
Besides their archaeological value, the nests also hold ecological information. Layers of bones, eggshells, and branches can reveal vulture eating habits, local wildlife, and how vegetation changed over centuries. Future studies might even identify traces of pesticides or pollutants in the preserved shells to offer insights that could be used in modern-day conservation practices.
A bearded vulture on a rock. Credit: David Ruh
Once found throughout southern Europe, bearded vultures suffered steep declines during the 19th and 20th centuries due to hunting, habitat loss, and reduced populations of wild animals. The birds were driven to extinction in southern Spain but have slowly begun to recover through reintroduction programs. However, the species is still endangered in the Mediterranean, with fewer than 250 individuals remaining.
The medieval nests of these bone-devouring birds have emerged as accidental archives—silent witnesses connecting Spain’s past with its natural heritage.
More information: Margalida, A., Couto, S., Pinedo, S. O., Gil-Sánchez, J. M., Agudo Pérez, L., & Marín-Arroyo, A. B. (2025). The Bearded Vulture as an accumulator of historical remains: Insights for future ecological and biocultural studies. Ecology, 106(9), e70191. doi:10.1002/ecy.70191
