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Guano - The bird excreta that almost started a World War


What is Guano?

Guano, a Spanish word derived from Quechua (an indigenous language spoken by the aboriginal people primarily living in the Peruvian Andes of South America), is referred to the accumulated excrement of seabirds and bats.

Humboldt Current

Also known as the Peru Current, the Humboldt Current is a cold ocean current of low salinity that originates from the southern tip of Chile and moves north along South America's western coast. This current helps to keep the coast one of the most intensely arid regions of the world. This cold flow is further intensified by the upwelling (caused by the combined effects of the drag of surface winds of the Southeast Trade winds and the Earth’s rotation) of the nutrient-rich deep waters. This upwelling along with sunlight on the surface waters cause rich plankton growth, which serves as food for anchovies, which in turn act as food for other bigger fishes.

The Humboldt current is one of the most productive marine ecosystems of Earth.

The Humboldt Current, Peruvian Coast and Guano

The richness of the ocean caused by the Humboldt current is not matched on land. The Andes mountains on the east of the Peruvian coast shield the shore from any warm moisture-laden winds from Brazil; and, as mentioned earlier, the cold Humboldt current on the west does not allow the air above to hold any moisture and thus renders the Peruvian shore dry and desolate. Equally dry and barren are Peru's other off-shore islands. While these coastal regions and islands are unsuitable for human habitation, the abundance of anchovetas and other fishes, make these islands and coasts alluring to sea birds, which have nested there for millennia. And, of course, over the years of occupying these barren lands, these birds have excreted wastes like all living creatures. These bird faeces - Guano - have accumulated in these lands (which have minimal or no rainfall) over the years, some of which are as high as 200 feet.

The Guano Islands

The Guano producing islands of Peru (Source:

The greatest sources of guano were the three (North, Central and South) Chincha Islands (shown on the map), located 21 kilometres from the city of Pisco in the Ica department of central Peru. These rocky, barren islands are comprised of volcanic rock. They are all less than one mile across and, apart from a couple of narrow beaches, are surrounded by high cliffs up to 300 feet high. Archaeological evidence suggests human visits to the island go back over a thousand years. Some of the artefacts, found deep under the layers of guano and soil, pre-date the Moche tribe from northern Peru who left evidence of their visits to the island, possibly for the purpose of mining guano, during the first millennium AD. Later came the Chincha tribe who ruled this part of Peru from the time of the Moche to just prior to their absorption into the rapidly expanding Inca Empire in the 15th century.

The Guano Producers

from left to right: Peruvian Pelican, Guanay Cormorant, White-Breasted Cormorant, Peruvian Booby (Source:

The seabirds that mainly roost on these islands are the White-Breasted Cormorant (Phalacrocorax lucidus), the Gray Pelican (Pelecanus philippensis), the Peruvian Pelican ((Pelecanus thagus), the Peruvian Booby (Sula variegata), and the Guanay Cormorant (Phalacrocorax bougainvillii).

Of all these seabirds, the Guanay Cormorant produces the richest and most plentiful guano. That is why it gets its name as 'Guanay' meaning 'the guano bird' by the natives.

What made Guano so important as to almost start a World War?

All of us are very well aware of the importance of fertilizers for plants, trees and various crops to grow and thrive. Fertilizers, which can be organic (composed of organic matter) as well as inorganic (made of inorganic chemicals or minerals), provide three major nutrients to the plants, viz., nitrogen, phosphorus and potassium, along with other secondary and trace nutrients.

The use of fertilizers has become such an integral part of modern farming that we seldom give a thought as to how it originated, where it comes from, how long has it been used, and how it affects our food production.

The present fertilizer practices are relatively recent and date back to the latter half of the 20th century. However, the traditional fertilizer practices are much more ancient. According to researchers from the University of Oxford, manure has been been used as fertilizer by farmers as early as 8000 years ago.

The use of guano as a fertilizer is thought to have been introduced by the Mocha tribe who lived from around 100 AD to 800 AD along the northern coast of Peru. In the 14th century, the Incas were thought to have extensively used the guano as a fertilizer. In fact, the guano was considered to be so important that they limited access to the islands and punished anyone who harmed the birds. However, in the 16th century after the Spanish invasion of the country, as the majority of the Incas were decimated or fell prey to disease, famines, or slavery, the use of guano declined and was forgotten.

One may wonder as to how the early farmers figured out the application of manure as the key to improving crop growth and yield? To this Amy Bogaard (archaeobotanist at the University of Oxford in the United Kingdom) and her colleagues suggest that the farmers may have observed super growth and fertile land in areas of 'natural dung accumulation' and may have thought of applying the same dung to their crops.
However, in those days farmers had no idea as to what constituents in manure actually contributed to crop growth and increase in yield. It was in the late 18th century up to the 19th century that scientists started experimenting with various minerals to enhance crop yields. And in 1840, a pioneer in organic chemistry, Justus von Liebig made a breakthrough discovery and stated that nitrogen-based fertilizer was needed to grow the healthiest possible crops. Along the way, he would be instrumental in suggesting the use of guano as an excellent source of nitrogen.

It was only in the early 19th century, when the European as well the American farmers were beginning to worry about their depleted soil quality and its ability to feed the growing population, the guano industry woke up from its slumber. Though the German explorer Alexander von Humboldt (who gave his name to the Humboldt Current) with the help of chemists like Sir Humphrey Davy rediscovered the richness of guano as a fertilizer (guano was found to be extremely rich in phosphorus and nitrogen - important ingredients for photosynthesis and growth, respectively) in the early 1800s (around 1802-1804), the potential of guano was not recognized for another 30 years.

In the year 1838, two businessmen from Lima, who had caught wind of guano's properties, shipped a couple of barrels of guano to Britain, where it was distributed to farmers as free samples. Guano worked extremely well compared to traditional fertilizers and increased the harvest; hence, farmers demanded for more. Over the next 15 years or so, the United Kingdom imported over two million tons of guano. And, shortly thereafter, guano demand rose in countries like Germany, France, and the United States.

Chincha Islands, Ships Waiting For Guano (1863)—Manuel González Olaechea y Franco Via Wikimedia Commons (

Chinese miners standing on the “Great Heap” demonstrate just how deep the seabird guano was in the Chincha Islands. From Alexander Gardner, “Rays of Sunlight From South America,” 1865.

And thus guano became the world's first fast-acting commercial fertilizer. A guano industry sprung up in the barren Peruvian littoral with new infrastructure, overnight millionaires, and widespread worker exploitation. To satisfy the expanding demand for guano, an army of workers comprising of native slaves, army deserters, prisoners, and later Chinese workers were put to work. The physical toll of guano harvesting was the same as that of mining, maybe even worse. The guano banks emanate a powerful acrid stench reminiscent of not-so-well-maintained public bathrooms. The workers faced horrific health effects as they had to endure extremely arduous conditions (breathing guano dust laden with toxic ammonia and potassium chloride), working up to 120 hours per week (an average of over 17 hours per day with no day off) under very hot, dry conditions.

Meanwhile, the debt-stricken (on account of the aftermath of both the War of the Confederation (1836–1839) and the War of Independence (1822–1825), a crushing debt default in 1826, and several hundred years as a Spanish colony) Peruvian government took advantage of its position, drove up the prices and counted its cash. In return, Britain cut an exclusive trade deal with the Peruvian government and took control over a majority of Peruvian guano (by the mid-1850s Britain was importing up to 300,000 tons of guano). Despite the tiny size of the Chincha islands, they were responsible for three-quarters of the government revenue.

However, the Britain-Peru alliance irked the United States as they had to purchase guano indirectly at a much higher cost. Therefore, in 1856 the Guano Islands Act was passed by the US government, allowing the American shippers and their business partners to acquire any unoccupied, unclaimed guano islands in the Pacific and Caribbean regions and strip them of their resources and then abandon them when no longer needed. Around 200 islands were claimed by the US due to this act.

The Spanish did not want to be left behind and in order to capture the guano trade, the Spanish troops occupied the Chincha Islands in April 1864. Fearing the loss of guano supply, the US and Britain threatened to retaliate. However, Peruvian and Chilean forces, and later forces from Ecuador and Bolivia, successfully defended the islands causing the Spanish to withdraw. Though a global war over guano was avoided at the last minute, the Chincha Islands war initiated several regional conflicts over resources which led up to the War of the Pacific (1879-1883), during which the hostilities between Peru, Bolivia and Chile played out. Also, according to Dr. Johnston, all the world's guano deposits were mined out by 1880 and the bird crap deposits that took thousands of years to develop almost vanished as the rate of demand was too high compared to the rate of production.

Also, as the 1900s rolled around, the world got the taste of new artificially manufactured chemical fertilizers before the fertilizer scarcity could be felt. They were easier to obtain, less smelly, and had the same effect (maybe even better) on plants as guano. So eventually, the guano demand died down considerably dragging down Peru's economy along with it.

Workers in Peru carry sacks of guano, which has risen in price due to fertiliser shortages brought about by the Russian invasion of Ukraine. (Source:

But, the guano craze isn't exactly over. The recent Russia-Ukraine war has led to a scarcity of fertilisers throughout the world as

Russia and Ukraine together export 28% of fertilizers made from nitrogen and phosphorous, as well as potassium. - Morgan Stanley.

Due to war and sanctions, disruptions in shipments have led to skyrocketing fertilizer prices. While other countries around the world wrestle and look for other alternative fertilizer sources, Peru has already turned back to its tried and tested fertilizer - guano. Also, the recent craze over organic foods has made people turn back to organic fertilizers, which created a small demand for guano, bird or bat, leading to the mining of guano again.

Let's hope that the next craze doesn't lead to a world war or a catastrophe.

Of course, we humans have proved time and again that when faced with adverse situations, we come out of it with solutions validating the saying 'Necessity is the mother of all inventions'.

The discovery of artificial fertilizers when guano was running out, or the lightning-fast discovery of COVID vaccines in more recent times are proof of that.








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