Guano is the excretion of seabirds, bats and seals. Guano consists of ammonia, uric acid, phosphoric acid, oxalic acid and carbonic acid and also has a high concentration of nitrates. The particularly high levels of phosphorus make this an effective phosphorus fertilizer. Guano was mined off the West Coast of South Africa as early as 1666. Since the 1840’s, large scale mining of guano caused the reserves to be depleted and mining was stopped by the turn of the century.