Other countries also used their desire for guano as a reason to expand their empires. The United Kingdom claimed Kiritimati and Malden Island for the British Empire. Other nations that claimed guano islands included Australia, France, Germany, Japan, and Mexico. Guano ended up at the centre of several conflicts. Peru, Chile, Bolivia and Spain went to war over guano-producing land, borders and taxes. Guano also helped to fuel the First World War thanks to its use as an ingredient in gunpowder.
All this doesn’t mean that guano was unknown before Western nations discovered it. It had been used in agriculture for more than 1,500 years. It was particularly treasured by the Inca Empire. Using bird guano as a fertiliser helped the empire to thrive, sustaining more than eight million people. It was so important to the Inca people that anyone who disturbed the seabirds faced the death penalty. The secret of guano’s fertilising power first spread to Europe in the mid-1500s, following Spain’s arrival and colonisation of South America. Guano’s popularity peaked in the nineteenth century – often called The Guano Age – and continued into the twentieth century.
These guano islands were not paradises. Guano accumulated only in extremely dry climates where the lack of rainfall allowed bird droppings to collect for centuries. Such islands were unpromising sites for human habitation. Guano mining — tunneling, picking, and blasting the stuff loose and hauling it to waiting ships — was arguably the single worst job you could have in the nineteenth century. Respiratory diseases, causing workers to pass out or cough up blood, and gastrointestinal ailments were common.
In all, about four hundred thousand tons of rock guano came off the islands the U.S. owned. Guano didn’t solve the soil exhaustion crisis, but, combined with Chilean sodium nitrates, which companies started selling later in the century, it held it at bay. Mined fertilizers kept industrial agriculture sustainable long enough for scientists to devise a more permanent solution. Demand for guano rapidly declined after 1910 with the development of the Haber–Bosch process for extracting nitrogen from the atmosphere.
Guano mining continues in Chile with the annual guano production in Chile ranging from 2,091 to 4,601 metric tons per year in the 2014–2023 period. With the rising popularity of organic food in the twenty-first century, the demand for guano has started to rise again.
But our demand for guano has also taken a toll on the birds that make it. At the peak of guano mining, it is estimated that that Peru’s coasts and islands were home to some 53 million seabirds. But guano mining sent some seabird populations spiraling into decline. One estimate states that these same Peruvian seabird populations had dropped to a mere 4.2 million by 2011. In the days of intensive guano extraction, important breeding grounds would have been disturbed by people year after year. Such disturbances cause entire colonies to abandon their nesting sites.
Losing large numbers of seabirds can have devastating consequences. Guano is a vital resource in nature. The nutrients that seabirds transport from marine environments and deposit as guano feeds plants and diverse invertebrate communities. The nutrients also trickle back into the ocean, helping tropical coral reefs to grow and recover from bleaching.
Guano is also the namesake for one of the nucleobases in RNA and DNA: guanine which was first obtained from guano.
