Guano (Spanish from Quechua: wanu) is the accumulated excrement of seabirds or bats. Guano is a highly effective fertiliser due to the high content of nitrogen, phosphate, and potassium, all key nutrients essential for plant growth. Guano was also, to a lesser extent, sought for the production of gunpowder and other explosive materials. The 19th-century seabird guano trade played a pivotal role in the development of modern input-intensive farming. The demand for guano spurred the human colonisation of remote bird islands in many parts of the world. Unsustainable seabird guano mining processes have resulted in permanent habitat destruction and the loss of millions of seabirds. Bat guano is found in caves throughout the world. Many cave ecosystems are wholly dependent on bats to provide nutrients via their guano which supports bacteria, fungi, invertebrates, and vertebrates. The loss of bats from a cave can result in the extinction of species that rely on their guano. Unsustainable harvesting of bat guano may cause bats to abandon their roost. Demand for guano rapidly declined after 1910 with the development of the Haber–Bosch process for extracting nitrogen from the atmosphere. Guano mining continues in Chile with the annual guano production in Chile ranging from 2,091 to 4,601 metric tons per year in the 2014–2023 period.
Composition and properties
Seabird guano Seabird guano is the fecal excrement from marine birds and has an organic matter content greater than 40%, and is a source of nitrogen (N) and available phosphate (P2O5).
Bat guano
Bat guano is partially decomposed bat excrement and has an organic matter content greater than 40%; it is a source of nitrogen, and may contain up to 6% available phosphate (P2O5).The feces of insectivorous bats consists of fine particles of insect exoskeleton, which are largely composed of chitin. Elements found in large concentrations include nitrogen, phosphorus, potassium and trace elements needed for plant growth. Bat guano is slightly alkaline with an average pH of 7.25. "The pH of the bat guano varies not only with age and storage conditions but also with the diet of bats": frugivorous bats have neutral to alkaline guano; insectivorous bats have acid guano.
History of human use
Bird guano
Indigenous use The word "guano" originates from the Andean language Quechua, in which it refers to any form of dung used as an agricultural fertiliser. Archaeological evidence suggests that Andean people collected seabird guano from small islands and points off the desert coast of Peru for use as a soil amendment and perhaps as long as 5,000 years. Spanish colonial documents suggest that the rulers of the Inca Empire greatly valued guano, restricted access to it, and punished any disturbance of the birds with death. The guanay cormorant is historically the most abundant and important producer of guano. Other important guano-producing bird species off the coast of Peru are the Peruvian pelican and the Peruvian booby.
Western discovery (1548–1800) The earliest European records noting the use of guano as fertiliser date back to 1548. Although the first shipments of guano reached Spain as early as 1700, it did not become a popular product in Europe until the 19th century.
The Guano Age (1802–1884)
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