The Chincha Islands off the coast of Peru are home to many seabird species that cover their island homes with thick layers of poop, or guano. New research now suggests that ancient Peruvians in the Chincha Valley on the Peruvian mainland hunted these seabirds, collected their guano, and used it to fertilize their maize crops, which helped expand pre-Inca societies.
The researchers analyzed ancient cobs of maize (Zea mays), some of them more than 2,200 years old, collected from archaeological sites in Peru. They found nitrogen levels in the maize that were much higher than natural soil conditions would allow. However, those nitrogen levels matched the levels found in 11 seabird species collected from the area, including the Peruvian booby (Sula variegata), Peruvian pelican (Pelecanus thagus) and guanay cormorant (Leucocarbo bougainvilliorum).
The match suggested that guano from seabirds that was used to fertilize the maize, which allowed the Chincha Kingdom to grow into a major civilization of 100,000 people. The Inca Empire farther inland took notice of the Chincha Kingdom’s crop success.
“The height of guano use was likely around AD 1250, which also represents the height of the Chincha Kingdom,” Jacob Bongers, lead author of the study with the University of Sydney in Australia, told Mongabay in an email. Bongers, a digital archaeologist, said it’s difficult to confirm details, but the Inca later controlled the Chincha Valley and “Chincha became the guano supplier for the Inca during this time.”
Jordan Dalton, an archaeologist at the State University of New York at Oswego, in the U.S., who wasn’t part of the fertilizer research, told Scientific American that there are still many mysteries about the Chincha Kingdom. “We know that they were a wealthy coastal polity — they had interactions and traded and competed with their neighbors — but we don’t really understand the nature of those social relationships and what kind of goods they were trading. There’s a lot that we need to fill in to really understand.”
The Inca Empire eventually absorbed the Chincha Kingdom and its valuable guano deposits. Bongers said they understood the importance of conserving the birds. “When the Inca gained control of the guano deposits, they forbade the killing of seabirds during their breeding seasons. The penalty was death.”
Banner image: A flock of Peruvian boobies. Photo courtesy of Alex Proimos via Wikimedia (CC BY 2.0)
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