The Islas Ballestas off the coast of the Chincha and Pisco valleys remain an important location for many seabird species, as well as seals and other marine animals. Birds today are less abundant than they were in the past, leading to decreased guano accumulation compared to earlier eras – credit, Jo Osborn
New archaeological evidence reveals that seabird guano—nutrient-rich bird droppings—may have the driver of behind the prosperity of the most influential pre‑Incan societies.
In ancient Andean cultures, fertilizer was power, said archaeologist Dr. Jacob Bongers, whose findings highlight the unexpectedly powerful role bird droppings played in shaping ancient societies in the Andes.
Farming on Peru’s coast is challenging, as it is one of the driest areas on Earth, where even irrigated soils quickly lose nutrients.
Guano shipped from offshore islands provided a potent, renewable fertilizer that allowed coastal farmers in the Chincha Valley to grow maize, one of the most important staple crops in the Americas, in abundance.
“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, Dr. Bongers from the University of Sydney said.
Published in PLOS One, Dr. Bongers and his study team analyzed biochemical signatures in 35 maize samples recovered from burial tombs in the Chincha Valley, home to a powerful coastal polity of perhaps 100,000 people.
Chemical analyses revealed exceptionally high nitrogen levels in the maize, far beyond the natural soil conditions typical for the area. This strongly indicates the crops were fertilized with seabird guano, which is enriched in nitrogen due to the birds’ marine diets.
“The guano was most likely harvested from the nearby Chincha Islands,” 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 researchers also examined regional archaeological imagery featuring seabirds, fish, and sprouting maize depicted together on textiles, ceramics, pottery, wall carvings and paintings, offering a further line of evidence that seabirds and maize held cultural importance in these ancient societies.
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“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.”
This agricultural surplus supported specialist merchants, farmers and fisherfolk, and helped the Chincha people to become major coastal traders.
The Inca, based in the highlands of the Andes, produced the largest native empire in the Americas before Europeans arrived and were famously obsessed with maize, using it to make ceremonial fermented beer, or ‘chicha’. But they couldn’t grow much of it in their highland environments, nor could they sail.
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“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.”
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