In speaking of guano, the Peruvians say, 'Aunque no sea santo hace Milagros' – Guano, though no saint, works miracles.

CUTHBERT WILLIAM JOHNSON, 'On Guano as a Fertiliser' (1843)



Guano – a natural fertiliser made of seabird and bat poo – is ultimately the product of the billions of anchovies that live off the coast of Peru in huge synchronised shoals. These anchovies are the largest fish catch by weight in the world, and they have created the planet’s largest bird colony: 10 million boobies, cormorants, gulls and penguins feed on the fish. The resultant droppings, known as guano, make such a powerful fertiliser that the Incas ranked it alongside gold as a gift from the gods, allotting the death penalty for anyone who molested the birds.
The secret of South American guano is the extremely dry climate. As most coastal environments are moist, useful nitrates evaporate very quickly from seabirds’ droppings. In coastal Peru, however, they dry almost immediately, locking in the important chemical nutrients.
In the 1840s, thousands of entrepreneurs raced to stake claims on the string of rocky Chincha islands off Peru where the guano lay up to 100 feet deep. Guano mining made coal extraction look like a beach holiday. The malodorous yellow substance was hard as concrete and could only be removed with dynamite or pickaxe. In the 1850s, the Peruvian President, Rámon Castilla was earning twice as much as Franklin Pierce, the US President.
Peru may be the only nation ever to have gone to war over bird poo – twice. The first time was the successful Peruvian campaign of 1866 to keep the Spanish out of the guano mines of Chincha. The second was a disastrous campaign to assert its rights in the nitrate-rich Atacama Desert against its much stronger neighbour Chile. Peru finally conceded defeat in 1883, by which time it had been reduced to bankruptcy and civilian riots.
Even though the development of inorganic fertilisers ended the guano rush, anchovy fishmeal is still Peru’s biggest export. Much of it goes to China to feed chickens. Sadly, Peruvians rarely eat the fish itself, believing it to be poisonous.


In the management of the kitchen, fruit and flower gardens, guano is producing wonderful changes…

The Guano Islands Act of 1856 authorizes US citizens to take possession of any unoccupied island with guano deposits.

Guano Grabs

In the 1850s, American farmers were so desperate for fertiliser that some had been reduced to putting hair, feathers and soot on their over-farmed soil to increase the yields of wheat, cotton and tobacco crops.
Phosphorus and nitrogen-rich guano looked like the answer. The discovery by Alexander von Humboldt of the massive deposits on the Peruvian coast in 1804 had triggered a guano rush, with the Peruvian government levying huge prices. The American response was to pass a special bill through Congress in 1856 called the Guano Islands Act. This granted the mining rights to any US citizen who landed and hoisted the stars and stripes on a previously unclaimed (and guano-laden) island. Almost a hundred Pacific and Caribbean islands were acquired in this way, including Christmas and Midway Islands. It has never been repealed.
One of the most notorious ‘guano-snatches’ was that of Navassa, near Haiti. It is now uninhabited except for giant iguanas, and for goats the size of ponies which were left by 17th-century pirates. In the late 19th century it was home to the notorious Navassa Phosphate Company where, in 1899, four white overseers were killed by black miners rioting against their appalling working conditions. The discovery of this shameful pocket of slavery caused outrage among liberal Americans; some historians credit the Navassa Riot with kick-starting the modern American labour movement. Navassa is also still subject to a formal claim by Haiti – it is the last US territory to be claimed by a foreign nation.

The Guanay Cormorant is sometimes known as ‘the most valuable birds in the World’ due to its guano deposits.

The word 'guano' comes from the Inca word huanu, meaning 'dung'.


Let us take a poor, sandy soil, which naturally produces no crop worth taking off: with the help of guano, we obtain, year after year, luxuriant produce.

El Guano

The climate pattern El Niño was first noticed by Peruvians in the 1800s due to the fall in guano production. El Niño caused falls in fish populations, which led to falls in seabird populations, which led to a lack of bird poo.

In the 1860s, guano accounted for 75% of Peru’s total revenue.