Every year, colonies of thousands of seabirds deposit tons of nitrogen and phosphorus through their excrement, known as guano, playing an important role in the nutrient cycle of coastal regions worldwide. An international group of researchers, including agronomist Tiago Osorio Ferreira from the Luiz de Queiroz School of Agriculture at the University of São Paulo (ESALQ-USP), analyzed the impact that seabird guano has on the nutrient cycle. The researchers estimated the global seabird population at 840 million individuals of 320 species distributed among 3,000 colonies. They then applied the data to a bioenergetic model, which considers the size of the bird, the food they eat, their energy efficiency, and how long they stay in breeding colonies, to infer the total amount of nitrogen and phosphorus excreted by the birds. Each year, they release 591,000 tons of nitrogen and 99,000 tons of phosphorus into the environment, primarily in colonies in the Arctic and Southern Oceans, which are inhabited by larger birds, such as the Macaroni Penguin (Eudyptes chrysolophus). “This is equivalent to the amount of nitrogen and phosphorus contributed to the ocean by all the rivers in the world,” explains Ferreira. In these regions, guano acts as a fertilizer for plants and as food for microbes (Nature Communications, January 23). Part of the excrement dissolves in the ocean, triggering chemical, biological, and geological processes on the coast. “Seabirds can play a key role in transferring nutrients from the ocean to land,” the researcher adds.