A new study in PLOS ONE links the rise of the Chincha Kingdom on Peru’s southern coast to seabird guano. Researchers combined chemical testing of crops, animal remains, archaeological evidence, and colonial records. Their results show that marine bird droppings enriched maize fields in one of the driest places on Earth and supported the growth of a large pre-Inca society.
The Chincha Valley lies along the desert coast of southern Peru. Farmers relied on irrigation from rivers flowing out of the Andes. Even with water, sandy soils lost nutrients quickly. About 25 kilometers offshore sit the Chincha Islands. Large colonies of guanay cormorants, Peruvian boobies, and pelicans nest there. Fed by rich fisheries created by the Humboldt Current, these birds produced thick layers of guano. The dry climate allowed the deposits to build up for centuries. Guano contains far more nitrogen and phosphorus than livestock manure, both of which are essential for plant growth.
To test whether farmers used this fertilizer, the research team analyzed 35 maize cobs from archaeological graves dated between about 1150 and 1675 CE. They also studied 11 seabird remains from contexts ranging from around 200 BCE to the Colonial period. The scientists measured stable nitrogen, carbon, and sulfur isotopes. Many maize samples showed high nitrogen isotope ratios. About half had extremely high values of δ15N. Such readings exceed those found in unfertilized desert soils and match crops grown with seabird guano in earlier field and archaeological studies in Chile.
Radiocarbon dates and isotopic patterns indicate that Chincha communities applied guano to maize fields by at least 1250 CE. The sulfur data overlapped with experimental results, though without strong enrichment, which the researchers link to environmental and cultural factors. Colonial documents describe coastal people traveling by raft to collect guano from offshore islands. Under Inca rule, officials restricted access during bird breeding seasons and imposed severe penalties for killing guano birds.
The Chincha Kingdom flourished between about 1000 and 1400 CE and may have included close to 100,000 people. Society was organized into fishers, farmers, and merchants. Higher maize yields would have supported population growth and long-distance trade along the Pacific coast. Chincha textiles, ceramics, and metal objects depict seabirds, fish, ocean waves, and sprouting maize. These images show an awareness of the link between marine life and agriculture.
In 1532, when Spanish forces led by Francisco Pizarro captured the Inca ruler Atahualpa at Cajamarca, Pedro Pizarro noted that the Lord of Chincha was the only other leader carried on a litter. Control over guano enriched agriculture likely strengthened Chincha’s political position within the Inca Empire. Around 1400 CE, the Inca incorporated Chincha after what sources describe as a peaceful capitulation.
The findings expand evidence for marine fertilization along the Andean coast. Stable nitrogen isotope analysis offers a reliable method for identifying past guano use, especially in places where material remains are limited. The study ties coastal ecosystems to agricultural output and political growth in pre-Hispanic Peru.
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