Guano


Guano 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 can result 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 and available phosphate.

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.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.
Chitin from insect exoskeletons is an essential compound needed by soil fungi to grow and expand. Chitin is a major component of fungal cell wall membranes. The growth of beneficial fungi adds to soil fertility.

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 for well over 1,500 years, 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)

In November 1802, Prussian geographer and explorer Alexander von Humboldt first encountered guano and began investigating its fertilising properties at Callao in Peru, and his subsequent writings on this topic made the subject well known in Europe. Although Europeans knew of its fertilising properties, guano was not widely used before this time. Cornish chemist Humphry Davy delivered a series of lectures which he compiled into an 1813 bestselling book about the role of nitrogenous manure as a fertiliser, Elements of Agricultural Chemistry. It highlighted the special efficacy of Peruvian guano, noting that it made the "sterile plains" of Peru fruitful. Though Europe had marine seabird colonies and thus, guano, it was of poorer quality because its potency was leached by high levels of rainfall and humidity. Elements of Agricultural Chemistry was translated into German, Italian, and French; American historian Wyndham D. Miles said that it was likely "the most popular book ever written on the subject, outselling the works of Dundonald, Chaptal, Liebig..." He also said that "No other work on agricultural chemistry was read by as many English-speaking farmers."
The arrival of commercial whaling on the Pacific coast of South America contributed to scaling of its guano industry. Whaling vessels carried consumer goods to Peru such as textiles, flour, and lard; unequal trade meant that ships returning north were often half empty, leaving entrepreneurs in search of profitable goods that could be exported. In 1840, Peruvian politician and entrepreneur negotiated a deal to commercialise guano export among a merchant house in Liverpool, a group of French businessmen, and the Peruvian government. This agreement resulted in the abolition of all preexisting claims to Peruvian guano; thereafter, it was the exclusive resource of the State. By nationalising its guano resources, the Peruvian government could collect royalties on their sale, which became the country's largest source of revenue. Some of this income was used by the State to free its more than 25,000 black slaves and to abolish the head tax on its Indians. This export of guano from Peru to Europe has been suggested as the vehicle that brought a virulent strain of potato blight from the Andean highlands that began the Great Famine of Ireland.
Soon guano was sourced from regions besides Peru. By 1846, of guano had been exported from Ichaboe Island, off the coast of Namibia, and surrounding islands to Great Britain. Guano pirating took off in other regions as well, causing prices to plummet and more consumers to try it. The biggest markets for guano from 1840-1879 were in Great Britain, the Low Countries, Germany, and the United States.
By the late 1860s, it became apparent that Peru's most productive guano site, the Chincha Islands, was nearing depletion. This caused guano mining to shift to other islands farther north and south. Despite this near exhaustion, Peru achieved its greatest ever export of guano in 1870 at more than. Concern of exhaustion was ameliorated by the discovery of a new Peruvian resource: sodium nitrate, also called Chile saltpetre. After 1870, the use of Peruvian guano as a fertiliser was eclipsed by Chile saltpetre in the form of caliche extraction from the interior of the Atacama Desert, close to the guano areas.
The Guano Age ended with the War of the Pacific, which saw Chilean marines invade coastal Bolivia to claim its guano and saltpetre resources. Knowing that Bolivia and Peru had a mutual defense agreement, Chile mounted a preemptive strike on Peru, resulting in its occupation of the Tarapacá, which included Peru's guano islands. With the Treaty of Ancón of 1884, the War of the Pacific ended. Bolivia ceded its entire coastline to Chile, which also gained half of Peru's guano income from the 1880s and its guano islands. The conflict ended with Chilean control over the most valuable nitrogen resources in the world. Chile's national treasury grew by 900% between 1879 and 1902 thanks to taxes coming from the newly acquired lands.

Imperialism

The demand for guano led the United States to pass the Guano Islands Act in 1856, which gave U.S. citizens discovering a source of guano on an unclaimed island exclusive rights to the deposits. In 1857, the U.S. began annexing uninhabited islands in the Pacific and Caribbean, totaling nearly 100, though some islands claimed under the Act did not end up having guano mining operations established on them. Several of these islands remain U.S. territories. Conditions on annexed guano islands were poor for workers, resulting in a 1889 rebellion on Navassa Island, where black workers killed their white overseers. In defending the workers, lawyer Everett J. Waring argued that the men could not be tried by U.S. law because the guano islands were not legally part of the country. The case went to the Supreme Court of the United States where it was decided in Jones v. United States. The Court decided that Navassa Island and other guano islands were legally part of the U.S. American historian Daniel Immerwahr claimed that by establishing these land claims as constitutional, the Court laid the "basis for the legal foundation for the U.S. empire".
Other countries also used their desire for guano as a reason to expand their empires. The United Kingdom claimed Kiritimati and Malden Island for the British Empire. Others nations that claimed guano islands included Australia, France, Germany, Hawaii, Japan, and Mexico.

Decline and resurgence

In 1913, a factory in Germany began the first large-scale synthesis of ammonia using German chemist Fritz Haber's catalytic process. The scaling of this energy-intensive process meant that farmers could cease practices such as crop rotation with nitrogen-fixing legumes or the application of naturally derived fertilisers such as guano. The international trade of guano and nitrates such as Chile saltpetre declined as artificially synthesised fertilisers became more widely used. With the rising popularity of organic food in the twenty-first century, the demand for guano has started to rise again.

Bat guano

In the U.S., bat guano was harvested from caves as early as the 1780s to manufacture gunpowder. During the American Civil War, the Union's blockade of the southern Confederate States of America forced the Confederacy to rely on guano mined from caves to produce saltpetre. One Confederate guano kiln in New Braunfels, Texas, had a daily output of of saltpetre, produced from of guano from two area caves.
From the 1930s, Bat Cave mine in Arizona was used for guano extraction, though it cost more to develop than it was worth. U.S. Guano Corporation bought the property in 1958 and invested $3.5 million to make it operational; actual guano deposits in the cave were 1% of predicted and the mine was abandoned in 1960.
In Australia, the first documented claim on Naracoorte's Bat Cave guano deposits was in 1867. Guano mining in the country remained a localised and small industry. In modern times, bat guano is used in low levels in developed countries. It remains an important resource in developing countries, particularly in Asia.