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 pelicans , and gannets . Bat guano is found in caves throughout the world, and {{link=seal">seal guano has accumulated to great depths on islands off northwestern Peru; both are lower in fertilizer value than bird guano.