New archaeological research suggests that seabird guano, nutrient-rich bird droppings, played a major role in transforming agriculture in ancient Peru and may have helped propel the Chincha Kingdom to prominence as one of the most prosperous and influential societies before the Inca.
Dr. Jacob Bongers, lead author of the study and a digital archaeologist at the University of Sydney as well as a Visiting Research Fellow at the Australian Museum Research Institute, said the findings reveal the surprisingly powerful impact bird droppings had on Andean civilizations.
“Seabird guano may seem trivial, yet our study suggests this potent resource could have significantly contributed to sociopolitical and economic change in the Peruvian Andes,” Dr. Bongers said.
“Guano dramatically boosted the production of maize (corn), and this agricultural surplus crucially helped fuel the Chincha Kingdom’s economy, driving their trade, wealth, population growth and regional influence, and shaped their strategic alliance with the Inca Empire.
“In ancient Andean cultures, fertilizer was power.”
Ancient Fertilizer Revealed Through Scientific Analysis
The research, published in PLOS One, examined biochemical markers in 35 maize samples recovered from burial tombs in the Chincha Valley. This region once supported a powerful coastal society with an estimated population of around 100,000 people.
Laboratory analysis showed extremely high nitrogen levels in the maize. These levels far exceeded what the surrounding soils could naturally produce. The results strongly suggest the crops were fertilized with seabird guano, which is rich in nitrogen because seabirds feed on marine life.
“The guano was most likely harvested from the nearby Chincha Islands, renowned for their abundant and high-quality guano deposits,” Dr. Bongers said. “Colonial-era writings we studied report that communities across coastal Peru and northern Chile sailed to several nearby islands on rafts to collect seabird droppings for fertilization.”
The team also studied archaeological artwork from the region. Images of seabirds, fish, and sprouting maize appear together on textiles, ceramics, pottery, wall carvings and paintings. These depictions provide additional evidence that seabirds and maize held deep cultural importance in these societies.
“Together, the chemical and material evidence we studied confirms earlier scholarship showing that guano was deliberately collected and used as a fertilizer,” Dr. Bongers said. “But it also points to a deeper cultural significance, suggesting people recognized the exceptional power of this fertilizer and actively celebrated, protected and even ritualized the vital relationship between seabirds and agriculture.”
Dr. Emily Milton, a postdoctoral fellow at the Smithsonian Institution in Washington, D.C., said combining multiple research approaches was key to understanding the practice.
“The historical records documenting how bird guano was applied to maize fields helped us interpret the chemical data and understand the regional importance of this practice,” she said. “Our work extends the known geographic extent of guano fertilization, echoing recent findings in northern Chile, and suggests soil management began at least around 800 years ago in Peru.”
Farming in One of the Driest Places on Earth
Agriculture along Peru’s coast has always been difficult because the region is among the driest environments on Earth. Even irrigated farmland quickly loses nutrients. Guano transported from offshore islands offered farmers a powerful and renewable fertilizer that made it possible to grow large quantities of maize in the Chincha Valley.
Maize was one of the most important staple crops in the Americas. The ability to grow it in abundance produced agricultural surpluses that supported merchants, farmers and fisherfolk. This prosperity helped the Chincha develop into major coastal traders.
“We know the Chincha were extraordinarily wealthy and one of the most powerful coastal societies of their time. But what underpinned that prosperity? Previous research often pointed to spondylus shells, the spiny oyster, as the key driver of merchant wealth,” Dr. Bongers said.
“Our evidence suggests guano was central to the Chincha Kingdom’s success, with the Chincha’s maritime knowledge and access to the Chincha Islands likely reframing their strategic importance in the region.”
Guano, Trade, and Relations With the Inca Empire
The Inca civilization, based high in the Andes, built the largest Indigenous empire in the Americas before European arrival. Maize held enormous cultural importance for the Inca and was used to make ceremonial fermented beer called ‘chicha’. However, growing large amounts of maize in the highlands was difficult, and the Inca did not have seafaring technology.
“Guano was a highly sought-after resource the Incas would have wanted access to, playing an important role in the diplomatic arrangements between the Inca and the Chincha communities,” Dr. Bongers said.
“It expanded Chincha’s agricultural productivity and mercantile influence, leading to exchanges of resources and power.”
Ecological Knowledge Behind Chincha Prosperity
Coauthor Dr. Jo Osborn of Texas A&M University said the findings encourage a broader rethink of how wealth and power functioned in the ancient Andes.
“The true power of the Chincha wasn’t just access to a resource; it was their mastery of a complex ecological system,” she said. “They possessed the traditional knowledge to see the connection between marine and terrestrial life, and they turned that knowledge into the agricultural surplus that built their kingdom. Their art celebrates this connection, showing us that their power was rooted in ecological wisdom, not just gold or silver.”
The study also builds on Dr. Bongers’ earlier research on the Band of Holes located just south of the Chincha Valley. He has suggested that this site may have served as an ancient marketplace operated by the Chincha Kingdom.
“This research adds another layer to our understanding of how the Chincha, and potentially other coastal communities, used resources, trade and agriculture to expand their influence in the pre-Hispanic era,” Dr. Bongers said.
Funding for archaeological field-work and isotopic analyses of maize samples was provided to JLB by the National Science Foundation Graduate Research Fellowship Program (DGE-1144087), the Society of Fellows at Boston University, the Ford Foundation Fellowship Program, the National Geographic Young Explorers Grant Program (9347-13), and the Sigma Xi Grants-in-Aid Research Program. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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