guano, dried excrement of sea birds and bats found principally on the coastal islands of Peru, Africa, Chile, and the West Indies. It contains about 6% phosphorus, 9% nitrogen, 2% potassium, and moisture. Guano is found mixed with feathers and bones and is used as a fertilizer.

Accumulated excrement and remains of birds, bats, and seals, valued as fertilizer. Bird guano comes mainly from islands off the coasts of Peru, Baja California, and Africa that are heavily populated by cormorants, pelicans, and gannets. Bat guano is found in caves throughout the world, and seal guano has accumulated to great depths on islands off northwestern Peru; both are lower in fertilizer value than bird guano.

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