New archaeological evidence reveals that seabird guano—nutrient-rich droppings—may have been the driving force behind the prosperity of the most influential pre-Inca societies.
In ancient Andean cultures, fertilizer was power, according to archaeologist Dr. Jacob Bongers, whose findings highlight the surprisingly powerful role that bird droppings played in shaping ancient societies in the Andes.
Farming on the coast of Peru is a challenge, as it is one of the driest areas on the planet, where even irrigated soils quickly lose nutrients.
Guano transported from nearby islands provided a potent, renewable fertilizer that allowed coastal farmers in the Chincha Valley to grow corn, one of the most important staple crops in the Americas, in abundance.
“Guano dramatically increased maize production, and this agricultural surplus crucially helped boost the economy of the Kingdom of Chincha, fostering its trade, wealth, population growth and regional influence, and shaping its strategic alliance with the Inca Empire,” said Dr Bongers of the University of Sydney.
Published in PLOS One, Dr. Bongers and his study team analyzed biochemical signatures in 35 corn samples recovered from graves in the Chincha Valley, home to a powerful coastal polis of perhaps 100,000 people.
Chemical analyzes revealed exceptionally high levels of nitrogen in the corn, far beyond typical natural soil conditions in the area. This strongly indicates that the crops were fertilized with seabird guano, which is rich in nitrogen due to the birds’ marine diet.
“The guano was most likely harvested from the nearby Chincha Islands,” Dr. Bongers said. “Colonial-era writings we studied report that communities along the Peruvian coast and northern Chile sailed to several nearby islands on rafts to collect seabird droppings for fertilization.”
The researchers also examined regional archaeological images showing seabirds, fish and corn sprouting together on textiles, ceramics, pottery, wall carvings and paintings, offering an additional line of evidence that seabirds and corn were culturally important in these ancient societies.
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“Together, the chemical and material evidence we studied confirms previous research showing that guano was deliberately collected and used as fertilizer,” Dr. Bongers said. “But it also points to a deeper cultural significance, suggesting that 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 specialized merchants, farmers, and fishermen, and helped the Chinchas become important coastal traders.
The Incas, based in the Andean highlands, produced the largest native empire in the Americas before the arrival of Europeans and were famously obsessed with corn, using it to make fermented ceremonial 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 coveted resource that the Incas would have wanted access to, playing an important role in diplomatic arrangements between the Incas and the Chincha communities,” Dr. Bongers said.
“It expanded the agricultural productivity and mercantile influence of Chincha, leading to exchanges of resources and power.”
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