The ancient Peruvian civilization capitalized on the harvesting of guano

A powerful fertilizer based on seabird droppings may have fueled the rise of Peru’s agricultural kingdom 900 years ago and helped lead to its eventual takeover by the Incas.

Chemical analyzes of ancient corn cobs from southern Peru show unusually high levels of nitrogen isotopes — telltale signs that the plants were fertilized by a mixture of seabird excrement, feathers and carrion known as guano. The findings provide the strongest evidence yet that Chincha’s indigenous farmers, fishermen and traders harvested this nutrient-rich fertilizer from nearby islands to improve inland crop fields — and boost their socioeconomic status, he says. Jacob Bongers at the University of Sydney.

“Privileged access to a vital resource is a path to power – which in this case the Chincha kingdom had and the Incas didn’t,” he says. “Social change may have come from a surprising source: bird droppings. It’s a fascinating story.”

Between 1000 and 1400, the wealthy and densely populated Chincha kingdom controlled one of the most productive coastal valleys in Peru before being incorporated into the Inca Empire in the 15th century.

The Chincha Valley is only 25 kilometers from the Chincha Islands – home to extensive colonies of Peruvian pelicans (Pelecanus thagus), Peruvian goats (Variegated garnet) and guanay cormorants (Leucocarbo bougainvilliorum), along with penguins and seagulls. These so-called Guano Islands they gained international fame in the 19th century for the fertilizing power of their bird droppingsmainly due to their exceptionally high nitrogen content.

The Inca’s use of guano is well documented in early colonial accounts that describe strict state control of the islands and heavy penalties for harming the birds. But until now, scientists have lacked solid archaeological evidence that their Chincha ancestors were already using this resource. Many historians have long argued that it did — and that access to seabird fertilizer fueled the kingdom’s economic success, Bongers says. Images of the seabird carved into ceremonial objects and depicted on textiles, ceramics, and architectural friezes further indicate that birds held special significance for the Chincha.

Bongers collected dozens of ancient ears of corn – “perhaps food for the dead” – from Chincha tombs and wondered if they might help solve the mystery.

He connected with Emily Milton at the Smithsonian Institution in Washington DC to analyze 35 ears of corn from 14 cemeteries in the Chincha Valley and measure their carbon and nitrogen isotope ratios. Bongers, Milton, and their colleagues also analyzed collagen from 11 ancient seabird bones from the region—including pelicans, cormorants, cormorants, gulls, and penguins—to establish a local isotopic baseline for the guano.

Bones from ancient seabirds showed elevated levels of nitrogen-15 typical of seabirds. Many corn ears showed even more extreme nitrogen isotope ratios, a hallmark of seabird guano fertilization.

The findings indicate that the Chinches were using the island’s resources at least as early as 1250, he says Yes Osborne at Texas A&M University.

Guano may have fueled the kingdom’s economic expansion and boosted its bargaining power when it was later incorporated into the Inca empire — with broader implications for how marine fertilizers shaped social change in the Andes, the researchers say.

“It makes a lot of sense that the ancient Peruvians used guano as fertilizer,” he says Dan Sandweiss at the University of Maine, who was not involved in the study. “It was a considerable expedition to get down there to the islands—but you do it for things of high value!”

The guano from Chincha Island is particularly valuable, probably because of the limited rainfall, he says, which allows the nitrogen to remain intact rather than leaching out. “This Peruvian guano was the real thing.

topics: