Bird poop powers rise of ancient Peruvian kingdom, analysis shows

The sociopolitical and economic expansion of the Chincha Kingdom in southern Peru was fueled by a surprising secret: the systematic use of seabird guano as a high-powered fertilizer.

A new study published in PLOS One provides the strongest evidence yet that Indigenous communities used marine fertilizers to supercharge maize production as early as 1250 CE, long before the Inca and Spanish empires dominated the region.

Researchers at the University of Sydney and Texas A&M University led the study; a critical component of this discovery took place at the University of California, Merced, directed by Professor Beth Scaffidi of the Department of Anthropology and Heritage Studies.

Scaffidi and her team used the Skeletal and Environmental Isotope Laboratory (SEIL) to prepare and analyze late pre-Hispanic maize cob fragments. By measuring chemical fingerprints in this ancient organic material, the UC Merced team reconstructed agricultural practices from nearly a millennium ago. Robin Trayer, technical director of UC Merced's core isotope analysis lab, assisted SEIL in its analysis.

To determine if ancient farmers were using guano, they analyzed stable carbon, nitrogen and sulfur ratios from maize cobs recovered from 26 tombs across 14 cemeteries in the Chincha Valley. Seabird guano is exceptionally rich in nitrogen. When farmers applied it to their fields, the plants absorbed this distinct isotopic signature.

The UC Merced also processed human hair from these archaeological sites and found similar isotopes. The team analyzed the remains of ancient cormorants, boobies, and pelicans — the primary guano producers — to establish a regional baseline for what "marine-enriched" nitrogen looks like in the Chincha environment.

The findings were definitive. The analysis revealed:

• Thirteen of the maize samples exhibited values at or above +20, a level no natural process or terrestrial fertilizer can achieve besides seabird guano. Some samples reached nitrogen levels as high as +27.4, confirming these crops were treated heavily with marine resources.
• These high nitrogen levels coincide with the Late Intermediate Period (1000–1400 CE), suggesting the Chincha Kingdom used guano to sustain a dense population of at least 30,000 people and a complex economy of farmers and merchants.
• Sulfur levels in the maize were consistent with experimental data from guano-fertilized plants, further supporting the conclusion that marine nutrients were the driving force behind coastal agricultural success.

The study concludes that seabird guano was not just a fertilizer but a catalyst for social change. It allowed the Chincha Kingdom to transform a desert landscape into one of the most productive riverine valleys in Peru. This agricultural sustainability likely made the region an attractive and valuable partner — and eventually a target — for the expanding Inca Empire.

“This research is important not only because it tells us when people started to intensify guano fertilizer usage, but because it can begin to tell us whether ancient people practiced resilient agriculture,” Scaffidi said

For example, she said, overuse of guano fertilizers can quickly strip soil of its nutrients and burn crops. In addition, mining for guano mining is toxic to miners and ocean animals in the vicinity, Scaffidi said.

Ancient Peruvians would have had to balance crop yield with risks from overuse of guano. “We’re only now starting to able to address how successful they were at that,” Scaffidi said.

Studying ancient cultures like the Chincha is vital because it offers a perspective on how societies adapt to environmental challenges. Understanding how past civilizations managed resources such as guano to achieve food security provides modern researchers with a blueprint for sustainable agricultural practices and a deeper appreciation for the ingenuity of Indigenous technologies.