An accumulation of the droppings of birds, bats, or seals, usually formed by a long-established colony of animals. It is rich in plant nutrients, and some deposits are extracted for use as fertilizer.
Geology and Earth Sciences
The leached residue of profuse accumulations of bird or bat excrement, rich in calcium phosphate. Such deposits are found particularly on arid oceanic islands and in caves. Guano is worked industrially as a phosphate resource.