Bird poo is worth an estimated £760m each year, according to new research.
Calculating the benefits could save gulls, pelicans, penguins and other species of conservation concern.
Ecologist Professor Marcus Cianciaruso, of the Federal University of Goias, Brazil, described the result as “staggering”.
He said: “Guano production is a service made by seabirds at no cost to us. I can go to an island, collect the guano, and sell it at market price as fertiliser.”
Only a small proportion is currently commercialised – but the rest has important nutrients for ecosystems where it is left.
The value of bird poo, also called guano, had never been worked out before now.
Prof Cianciaruso said: “Because there is this scientific and biological importance, it is possible to quantify seabird ecosystem services in a language the general public and policymakers can begin to understand.”
Some seabirds, including gulls and pelicans, are often overlooked when it comes to threatened wildlife. They struggle to capture the public eye.
The South American team believe the key lies in focusing on their poo.
They found it is worth around $1 billion annually (£760 million).
The researchers began by gathering data about seabirds across the world whose guano is turned into a product.
Co author Daniel Plazas-Jimennez, a PhD student, explained: “Because guano is a commodity, we used its market price to estimate the added value of guano produced by seabirds each year.”
For the other birds, they estimated the cost of replacing the nitrogen and phosphorus deposited every year in their colonies with inorganic versions.
Prof Cianciaruso said: “The result is staggering. When combined, the nutrient deposition and the guano could be worth an estimated $473.83 million per year (£360 million).”
Not all poo can be commercialised but its nutrients are vital to ecosystems such as coral reefs.
Its presence can increase the number of fish by almost 50%.
Mr Plazas-Jimenez said: “We made a very conservative estimate that ten percent of coral reef fish stocks depend on seabird nutrients.
“According to the United Nations and the Australian government, the annual economic returns of commercial fisheries on coral reefs is over $6 billion (£4.5bn). So, 10% of this value is around $600 million (£450 million) per year.”
When added to the previous figure, the value of nutrients deposited by seabirds increases to an estimated $1 billion ( £760 million).
The study published in Trends in Ecology & Evolution also shows much of this comes from threatened or endangered species.
Mr Plaza-Jimenez said: “The example of coral reefs is just for a little group of seabirds. A huge amount of nutrient deposition happens in Antarctic ecosystems.
“Penguins contribute half of the nitrogen and phosphorous deposited by seabirds every year.
“However, 60% of this contribution is made by penguin species with declining populations, and these contributions will decrease in the future if no conservation activity is taken.”
The researchers hope the groundbreaking paper will shed light on how valuable these species are on a global scale.
Climate change and loss of habitat may wipe many out.