Review quantifies birds’ role as nutrient transporters

A review of nearly 400 scientific papers concludes that birds are major nutrient transporters, moving resources obtained from food into waste and depositing them across oceans, forests, lakes and coral reefs. Researchers from Cornell University and five other institutions synthesized evidence that these transfers can influence soil and water chemistry, plant and algae growth, and the feeding grounds available to other animals. Published in Current Biology, the review describes birds as efficient nutrient-processing systems whose mobility allows them to carry resources across barriers such as oceans and mountains. Lead author Ethan Duvall said birds concentrate nutrients in their waste and deposit them in places where they can become valuable resources for plants and other organisms.

The scale of this process is linked to the distinctive biology of birds. Their ability to fly gives them access to widely separated feeding areas, nesting sites and roosts, while their food consumption rates are about 30% higher than those of similarly sized mammals, according to Duvall. Birds feed on seeds, insects, invertebrates and fruits containing nitrogen and phosphorus, and they release those nutrients at elevated rates. The reviewers found that concentration sites such as nesting colonies and communal roosts can receive high local nutrient inputs. These “islands of fertility” can stimulate plant or algae growth and provide richer feeding opportunities for insects and other vertebrates that consume those producers, creating cascading effects through the local food web.

Seabirds offer a particularly strong example of how bird-mediated transport links separate environments. Nutrients associated with seabird colonies can reach nearby coastal waters and support coral reefs and fish communities. Across the studies surveyed, the disappearance of seabird colonies was associated with lower nutrient levels, reduced plant and algae productivity, lower reef-fish biomass and diminished coral-reef resilience to environmental stress. The review also examined a restoration study in which seabird perches installed within a seagrass restoration site attracted birds that deposited large amounts of phosphorus. The birds’ phosphorus input helped the seagrass recover. Duvall said this result shows the potential for using birds’ capacity to transport recycled nutrients in restoration efforts, while the evidence presented concerns that specific seagrass study rather than demonstrating a universal restoration method.

A separate study by Duvall, Linsey Chen and Alexander Flecker measured how seasonal dietary changes alter the nutrients released by a local songbird community. The researchers analyzed bird waste at the Braddock Bay Bird Observatory on Lake Ontario in spring 2021 and fall 2022. When birds ate more insects in spring, their waste was richer in nitrogen; when their diets shifted toward fruits and seeds in autumn, it was richer in carbon. Published in Functional Ecology in March, the study shows that body size, behavior, diet and seasonal variation affect both the amount and composition of nutrients released by birds. This variation means that the contribution of a bird community cannot be characterized solely by its total abundance: the species present, their diets and the seasons in which they are present also shape the nutrient inputs received by an ecosystem.

The synthesis places that local variability within a much larger geographic pattern. By connecting feeding areas to nesting and roosting sites, birds can redistribute resources and influence productivity across terrestrial and aquatic environments. The authors said ecologists have long known that birds transport nutrients, but the review consolidates evidence concerning the magnitude and geographic scale of their role. The research also provides a basis for examining how population declines could affect ecosystem function. Citing the State of the World’s Birds report, the news release said 45% of global migratory bird species are declining. Duvall said ecosystems may consequently become less fertile and productive, and that these changes may affect their ability to sequester carbon. The review does not quantify a universal effect for every declining population, but it identifies bird-mediated nutrient movement as an ecological mechanism through which losses of birds may produce broader changes in nutrient supply and ecosystem processes.

Subject of Research: Bird-mediated nutrient transport and its effects on ecosystem productivity

Article Title: Birds are among Earth’s most important nutrient-movers

Article References: Birds are among Earth’s most important nutrient-movers. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: bird nutrient transport, nutrient cycling, seabirds, songbirds, coral reefs, seagrass restoration, phosphorus, nitrogen, ecosystem productivity, migratory bird declines, Birds, Earth