Guano is the accumulated excrement of seabirds and bats. As a manure, guano is a highly effective fertilizer due to its exceptionally high content of nitrogen, phosphate and potassium: nutrients essential for plant growth.Seabird guano consists of nitrogen-rich ammonium nitrate and urate, phosphates, as well as some earth salts and impurities. Bat guano is faecal excrement from bats. Commercially harvested bat guano is used as an organic fertilizer. All commercially sold bat guano is derived from insect-eating bats.