From London's Ghost Acres
Guano is bird droppings, used as a fertilizer that has high nitrogen, phosphate and potassium content. Guano was first harvest from the Peruvian Chincha Islands in the 1840s and played a significant role in US expansion across the Pacific, due to the Guano Islands Act of 1856. Guano was also the basis of a war between Spain and a Peruvian-Chilean alliance, the Chincha Islands War from 1864–1866. Guano lost popularity after 1870 when it was replaced by saltpeter from the interior of the Atacama Desert.