Unlikely as it might seem today, bird poop was once a hot commodity. In the 19th century, guano—the excrement of seabirds and bats—was prized by American farmers as an effective natural fertilizer, full of nitrogen and phosphorous.
In fact, in 1856 Congress passed the Guano Islands Act, giving any American citizen who discovered an uninhabited island with deposits of guano the right to mine it and claim the land for the U.S., as long as it wasn’t in the jurisdiction of another government. The president was even authorized to send in the military to protect the island, and the U.S. had the option to drop its claim to an island after the guano was depleted.
Peru initially cornered the guano market and commanded steep prices for the stuff, which it exported to Europe and America in vast quantities. The country’s Chincha Islands were home to large populations of seabirds, who over the centuries had blanketed the terrain in mountains of guano. The bird waste there was mined by Chinese laborers, prisoners and others. But then Congress stepped in, to try to help Americans gain a foothold in the thriving industry.
However, Senator William Seward, who later became known for negotiating America’s purchase of Alaska in 1867 when he was secretary of state, sponsored the legislation. The U.S. went on to claim dozens of guano islands, most of them in the Caribbean and Pacific, including Midway Atoll, later the site of the Battle of Midway in World War II. The guano law is now largely seen an early act of American imperialism.
By the 20th century, American farmers had turned to synthetic fertilizers and the demand for guano plummeted. However, guano continues to be used by some organic farmers to this day. And, in case you stumble across an unoccupied, bird-poop filled piece of land that doesn’t belong to anyone, you can claim it, as the Guano Islands Act is still on the books.