Hank: Throughout history, humans have prized a lot of animals for making products that we find beautiful or useful. Silkworms for their silk, whales for their blubber, sheep for their wool.

But in the mid-1800s, a bird called the Guanay cormorant was considered the most valuable in the world! It was nicknamed the ‘billion dollar bird,’ because its poop, or guano, was an amazing fertilizer.

At the beginning of the 19th century, populations were exploding – and all those people needed to eat. Large-scale agriculture had been booming for a few hundred years, and soils were quickly getting depleted of nutrients.

Enter Alexander von Humboldt, European explorer extraordinaire. While exploring the coast of Peru in 1802, von Humboldt came across workers unloading a shipment of guano from the Chincha Islands. Indigenous cultures in the area had been using the guano on these islands as a source of fertilizer for hundreds of years, so von Humboldt definitely didn’t discover guano.

But, like any good explorer, he took a sample of it back with him to Europe. And at the time, people didn’t know much about the science of fertilizers. Farmers recognized that adding things like ground-up bones, ash or feces to soil helped plants grow, but scientists weren’t sure why this worked.

We now know the answer is elementary. Actually elementary — like literally it’s elements that are involved. These materials all have a lot of nitrogen, phosphorus, and other elements that help plants grow.

Plants use nitrogen to make important proteins and pigments, like chlorophyll, which lets them absorb sunlight and do photosynthesis and not die. Phosphorus is needed to make DNA and RNA, as well as cell membranes and the molecules all living things use to make and store energy. Without these elements, plants can’t make more cells or even function with the cells they have.

But even if scientists had known this at the time, it wouldn’t have helped them very much – there just weren’t many good sources of nitrogen and phosphorus that plants could use. There’s plenty of nitrogen in the air, of course, but plants can’t just suck it in like carbon dioxide. They usually rely on bacteria in soil to convert, or fix, the nitrogen into a slightly different form -- like nitrate or ammonium --- that they can actually use.

If the soil has been exhausted of these chemicals, it’s really hard to grow crops. Which brings us back to the Chincha Islands.

It turns out, bird guano is amazingly rich with these sources of fixed nitrogen and phosphorus. In fact, it’s even better than cow dung or horse dung. Cows and horses only eat plants. But Guanay cormorants feast almost entirely on anchovy-like fish.

That protein-rich diet means a lot of nitrogen eventually shows up in their poop! Plus, bird poop is really poop and pee combined, so that’s extra nitrogen and phosphorus that other animal dung leaves out. As for why this natural fertilizer could just pile up, thank the dry climate of coastal Peru.

In most of the world, bird poop will simply get washed away, but ocean currents from Antarctica ensure it almost never rains on the islands, allowing guano to harden, locking in layer upon layer upon layer of nitrate-phosphate goodness. So, when word finally reached Europe that von Humboldt had potentially found a great new source of fertilizer... they went crazy for it.

Almost immediately, the Peruvian government started huge mining operations, selling the guano to any country that wanted it. Other countries got involved, too. In 1856, the United States even went so far as to pass the Guano Islands Act, which allowed American citizens to claim any island they wished, so long as it had guano on it and wasn’t already claimed by another country.

Guano miners came from all over the world, harvesting the seemingly limitless resource. But while the guano boom was great for agriculture, it was bad news for the Guanay cormorant and other seabirds that called the islands home. Miners ate the birds and their eggs -- which was not really smart, when you think about it -- and destroyed their habitat to the point that their populations began to fall. By the 1870s, most of the guano on these islands had been already been mined.

A few decades later, Peru started protecting the remaining cormorants -- it’s one of the first examples of a government stepping in to protect a natural resource. But for the guano industry, it was too late. With fewer droppings to mine, and the discovery of artificial fertilizer, the guano boom went bust.

German chemist Fritz Haber had figured out how to fix nitrogen from the air and turn it into ammonia, which could in turn be used to develop synthetic fertilizers. These worked just as well, if not better, than guano. And now we’ve been using these fertilizers for decades to feed billions of people.

But guano might not have outlived its usefulness just yet. Recently, the rise of organic farming has increased demand for high-quality organic fertilizers, and guano is one of the best.

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