It was a treasure for the Incas, the cause of a war, and once a backbone of Peru's economy.
Now as the world hungers for sustainable resources, bird excrement is once again as prized as gold.
And a handful of islands off the nation's Pacific coast are literally dripping in tons and tons of one of its most historic treasures: guano.
Here millions of birds, fed by anchovy-rich waters, poop around-the-clock, discharging a dirty, potent, fishy cocktail of phosphates and nitrates.
"It is a natural, organic fertilizer and Peru is the only place in the world that it is exploited commercially in this way," said Rodolfo Beltran, director of Agrorural, Peru's rural development agency.
"It has been a historical commodity in Peru and now it's making a comeback. It has a great future."
Peru is the world's top producer of guano, far ahead of Chile and Namibia.
During the nation's guano boom from the 1840s to the 1880s, the proceeds from bird poo accounted for most of Peru's national budget. It was the country's other "gold."
Thousands of indentured Chinese laborers, convicts and deserters died extracting guano. Even the War of the Pacific (1879-1883) between Peru and Chile was indirectly caused by a dispute over access to the commodity.
Now Peru is taking a more sustainable approach to this oddest of natural resources. "It's a treasure of Peru, we are the only one in the world to have that," said Beltran.
It all starts with looking after the guano producers; the Guanay cormorant, the Peruvian booby, the pelican and the marine ecosystem in which they thrive.
On one of the 21 islands, Guanape Sur, some six kilometers (three miles) from the coast of Lambayeque in northern Peru there are more than half a million birds.
They own the skies and compete for almost every inch of the tiny island for nesting space. The by-product is thousands of tons of guano, which is meters (feet) deep in places.
Under a constant drizzle of bird droppings, around 280 laborers do the back-breaking work of collecting and bagging the guano into 50-kilogram (110-pound) sacks to be winched onto waiting barges and towed to Salaverry, the port of the northern Peruvian city of Trujillo.
They expect to collect some 23,000 tons of it this year.
Once the guano is processed, it can be sent abroad, onto a market keen for organic fertilizers where it can command a high price tag.
But unlike in the past, when over 200,000 tons a year were exported, most of the guano is used domestically, distributed to around a million small organic farmers, especially in areas where the soil has been degraded.
Here a combination of cold water and warm air currents means there is little rainfall so the nitrates do not evaporate or leach into the rock and the sunshine dries the guano making it the best and most abundant in the world.
Generations of hardy farmers have done this back-breaking seasonal work, most hailing from the Andean highlands in Peru's Ancash region.
They can earn more than double Peru's minimum wage of 550 soles (196 dollars), scaling the islands narrow pathways before dawn. But the pace is relentless and many shoulder some 120 such heavy sacks of guano a day.
In Peru, they say such workers have the "punche." It means muscle or power and these laborers, who wear no protective gear, have it in spades.
Their short and often slight frames belie their stamina. Squint and you will see a scene which has not changed for centuries with modern labor saving techniques set aside in order not to disturb the birds.
After eight months on the islands, most workers pack up and head home for a break. Leaving behind a lone guard to stand vigil and protect the birds and their precious waste from poachers.
"It gets lonely, as you miss your family," Juan Mendez said. "But it is actually a nice job working with the birds."
"The poachers can kill up to 200 birds in a single night," he said. "They stun them with bright torch light and use a stick to kill them. Then they sell their meat... in cheap coastal markets."
The seabird population has doubled in the last five years to five million, but that barely compares with the 60 million birds at the peak of the guano boom.
While the days of over-exploitation and conflict are gone, the birds are still threatened by overfishing and the, as yet, uncertain impact of climate change.
The birds rely on Peru's rich coastal waters which contain some 80 percent of the world's biomass of anchovy and enables them to breed in such numbers.
But the Humboldt current which pushes cold water from the Antarctica up to the equator is crucial for this natural balancing act, and when it strays from Peru's coastal waters during the seasonal El Nino weather phenomenon the impact on this marine ecosystem can be devastating.
During such times tens of thousands of seabird chicks or eggs perish, said Mendez, who has spent the last 13 years guarding the guano islands along its 3,000-kilometer coast.
But with such careful vigilance Peru's guano windfall seems likely to survive, much as it has since the time of the Incas, who were the first to collect what they called "wanu" and punished anyone caught disturbing the birds with death.
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