Guano (from the Quechua 'wanu', (dung) via Spanish) is the excrement (feces and urine) of seabirds, cave dwelling bats, and seals. Guano manure is an effective fertilizer due to its high levels of phosphorus and nitrogen and also its lack of odor. It was an important source of nitrates for gunpowder. Soil that is deficient in organic matter can be made more productive by addition of this manure.
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Guano consists of ammonium oxalate and urate, phosphates, as well as some earth salts and impurities. Guano also has a high concentration of nitrates. Bird guano has a fertilizer analysis of 11 to 16 percent nitrogen, 8 to 12 percent equivalent phosphoric acid, and 2 to 3 percent equivalent potash.[1] Bat and seal guano are lower in fertilizer value than bird guano.
The word "guano" originates from the Quichua language of the Andes and means "the droppings of sea birds". Andean peoples collected guano from the coast of Peru for use as soil enricher. The rulers of the Inca Empire assigned great value to guano, restricting access to it and punishing any disturbance to the birds with death.[2]
Guano has been harvested over several centuries along the coast of Peru, where islands and rocky shores have been sheltered from humans and predators. The Guanay Cormorant has historically been the most important producer of guano; its guano is richer in nitrogen than guano from other seabirds. Other important guano producing species off the coast of Peru are the Peruvian Pelican and the Peruvian Booby.
In November 1802, Alexander von Humboldt studied guano and its fertilizing properties at Callao in Peru, and his subsequent writings on this topic made the subject known in Europe.
The high concentration of nitrates also made guano an important strategic commodity. The discovery during the 1840s of the use of guano as a fertilizer and its Chile saltpetre content as a key ingredient in explosives made the area strategically valuable.
In this context the US passed the Guano Islands Act in 1856 giving citizens discovering a source of guano the right to take possession of unclaimed land and entitlement to exclusive rights to the deposits. However, the guano could only be removed for the use of citizens of the United States.[2] This enabled US citizens to take possession of unoccupied islands containing guano.
Control over guano played an important role in the Chincha Islands War (1864-1866) between Spain and a Peruvian-Chilean alliance since Spain occupied with its navy the Chincha Islands depriving Peru of lucrative income.
In the second half of the 19th century guano extraction was eclipsed by salpeter in the form of caliche extraction from the interior of Atacama Desert, not far from the guano areas. After the War of the Pacific (1879-1883) Chile seized much of the guano as well as salpeter producing area making its national treasury grow by 900% between 1879 and 1902 due to taxes coming from the newly acquired lands.[3]
By the end of the 19th century, the importance of guano declined with the rise of artificial fertiliser, although guano is still used by organic gardeners and farmers.[2] Superphosphate made from guano is used for aerial topdressing.
The ideal type of guano is found in exceptionally dry climates, as rainwater drains the guano of nitrates. Guano is harvested on various islands in the Pacific Ocean (for example, the Chincha Islands) and in other oceans (for example, Juan de Nova Island and Christmas Island). These islands have been home to mass seabird colonies for many centuries, and the guano has collected to a depth of many metres. In the 19th century, Peru was famous for its supply of guano.
Bat guano is usually mined in caves and this mining is associated with a corresponding loss of troglobytic biota and diminishing of biodiversity. Guano deposits support a great variety of cave-adapted invertebrate species, which rely on bat faeces as their sole nutrient input. In addition to the biological component, deep guano deposits contain local paleoclimatic records in strata that have built up over thousands of years, which are unrecoverable once disturbed.
The greatest damage caused by mining to caves with extant guano deposits is to the bat colonies themselves. Bats are highly vulnerable to regular disturbance to their roosts. Some species, such as Phyllonycteris aphylla, have low fat reserves, and will starve to death when regularly disturbed and put into a panic state during their resting period. Many species will drop pups when in panic, with subsequent death, leading to a steady reduction in population. Research in Jamaica has shown that mining for bat guano is directly related to the loss of bat species, associated invertebrates and fungi, and is the greatest threat to bat caves on the island.
In agriculture and gardening guano has a number of uses, including as: soil builder, lawn treatments, fungicide (when fed to plants through the leaves), nematicide (decomposing microbes help control nematodes), and as composting activator (nutrients and microbes speed up decomposition).[2]