Seabird Poop Is Worth More Than $1 Billion Annually

Scientists put a price tag on guano’s global benefits, which range from agricultural fertilizer to coral reef enricher

Seabird guano
Guano stains the cliffs of a gannet breeding colony in Shetland Education Images/Universal Images Group via Getty Images

When Don Lyons, director of the Audubon Society’s Seabird Restoration Program visited a small inland valley in Japan, he found a local variety of rice colloquially called “cormorant rice.” The grain got its moniker not from its size or color or area of origin, but from the seabirds whose guano fertilized the paddies in the valley. The birds nested in the trees around the dammed ponds used to irrigate the rice fields, where they could feed on small fish stocked in the reservoirs. Their excrement, rich in nitrogen and phosphorus, washed into the water and eventually to the paddies, where it fertilized the crop.

The phenomenon that Lyons encountered is not a new one—references to the value of bird guano can be found even in the Bible, and an entire industry in South America grew around the harvesting of what many called “white gold.” What is new is that scientists have now calculated an exact value for seabird poop. This week, researchers published a study in Trends in Ecology and Evolution that estimates the value of seabird nutrient deposits at up to $1.1 billion annually. “I see that [many] people just think you care about something when it brings benefits, when they can see the benefits,” says Daniel Plazas-Jiménez, study author and researcher at the Universidade Federal de Goiás in Brazil. “So, I think that is the importance of communicating what seabirds do for humankind.”

Given that 30 percent of the species of seabirds included in the study are threatened, the authors argue that the benefits the birds provide—from fertilizing crops to boosting the health of coral reefs—should prompt global conservation efforts. Government and interested parties can help seabirds by reducing birds accidently caught during commercial fishing, reducing the human overfishing that depletes the birds’ primary food source and working to address climate change since rising seas erode the birds’ coastal habitats and warming waters cause the birds’ prey fish to move unpredictably.

To show the benefits seabirds provide, Plazas-Jiménez and his coauthor Marcus Cianciaruso, an ecologist at Goiás, set out to put a price tag on the animals’ poop. Scientists and economists lack sufficient data on the direct and indirect monetary gains from guano. So the ecologists had to get creative; they used a replacement cost approach. They estimated the value of the ecological function of bird poop as an organic fertilizer against the cost of replacing it with human-made chemical fertilizers.

Guano bags ready for sale
Guano bags ready for sale and distribution in Lima, Peru Photo by Manuel Medir/Getty Images

Not all seabirds produce guano, which is desiccated, or hardened, excrement with especially high nitrogen and phosphoric content, so the authors took a two-step process to figure out how much waste the birds produce. First, the authors calculated the potential amount of poop produced annually by guano-producing seabirds based on population size data. They valued the guano based on the mean international market price of Peruvian and Chilean guano, which represented the highest-grossing product. Next the scientists estimated the value produced by non-guano-producing seabirds, who also excrete nitrogen and phosphorus. The researchers valued the chemicals based on the cost of inorganic nitrogen and phosphorus traded on the international market. The primary value of the poop based on replacement costs was around $474 million.

The scientists then estimated that ten percent of coral reef stocks depend on nutrients from seabirds, a back of the envelope number that they admit needs more study. Since the annual economic return of commercial fisheries on Caribbean reefs, Southeast Asian reefs and the Great Barrier Reefs is $6.5 billion, the scientists estimated secondary economic benefits from seabird guano to be at least $650 million. That brought the estimated total benefit of guano up to $1.1 billion.

Still, that number, Lyons says, is likely a pretty significant underestimate since there are secondary benefits to not producing chemical fertilizers. “Another aspect of that is the replacement product, fertilizers, are generally derived from petroleum products,” says Lyons. “And so, there's a climate angle to this—when we can use more natural nutrient cycling and not draw on earth reserves, that’s a definite bonus.”

Though the billion dollar-plus price on poop is impressive, it is likely much lower than the comparative value before seabird numbers declined over the past roughly 150 years. The richness of guano in South America, particularly on the nation’s Chincha Islands, has been documented for centuries. Birds nest along the island’s granite cliffs where their excrement builds up and the hot, dry climate keeps it from breaking down. At one point, an estimated 60 million birds—including guanay cormorants, boobies and pelicans—built 150-foot-high mounds of poop. The Incans were the first to recognize guano’s agricultural benefits, supposedly decreeing death to those who harmed the seabirds.

By the early 1840s, guano became a full-blown industry; it was commercially mined, transported and sold in Germany, France, England and the United States. The 1856 Guano Islands Act authorized one of the United States’ earliest imperial land grabs outside of North America, stating that the nation could claim any island with seabird guano, as long as there were no other claims or inhabitants. This paved the way for major exploitation and the establishment of Caribbean, Polynesian and Chinese slave labor to work the “white gold” mines.

The industry crashed around 1880 and revived in the early 20th century. Today, interest in guano is resurgent as consumer demand for organic agriculture and food processing has risen. However, only an estimated 4 million seabirds now live on the Chincha islands, drastically reducing the amount of guano produced. This loss is part of a global trend. According to one study, the world’s monitored seabird populations have dropped 70 percent since the 1950s.

The decline of seabird populations, says Plazas-Jiménez, is devastating to local cultures that have used the organic fertilizers for generations, local economies that depend on fisheries, and the world’s biodiversity. One study found that guano nutrient run-off into the waters of the Indian Ocean increasing coral reef fish stocks by 48 percent. Another study found that dissolved values of phosphate on coral reefs in Oahu, Hawaii, were higher where seabird colonies were larger and helped to offset nutrient depletion in the water caused by human activities.

Improving the health of coral reefs is important. Roughly a quarter of ocean fish depend on nutrient-rich reefs to survive. And seabirds’ contributions to coral reef health provide ecosystem services beyond increasing fish stocks; they also drive revenue through tourism and coastline resilience. Coral reefs function as important natural bulkheads protecting remote island and coastal communities from storm erosion and rising water. “It's really compelling to think in terms of billions of dollars, but this is also a phenomenon that happens very locally,” says Lyons. “And there are many examples of where unique places wouldn’t be that way without this nutrient cycling that seabirds bring.”

Get the latest Science stories in your inbox.