Guano
Sediment formed from long accumulations of seabird or bat droppings. Rich in nitrogen and phosphorus, it was traded internationally as agricultural fertilizer in the 19th century.
Emperor penguin colonies can show up in satellite images as poop stains before the birds are visible. Brown guano patches on Antarctic ice are detectable by 10 m-resolution Sentinel-2 imagery, letting researchers find new colonies from space.
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Guano, formed from accumulated seabird droppings, was so valuable as fertilizer and gunpowder material that it sparked wars. In 1856, the USA passed the Guano Islands Act, allowing it to claim any uninhabited island with guano deposits—and the law remains in effect today.
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