Sea Level Rise Poses Growing Threat to Migratory Shorebirds, Study Finds

Feb. 25, 2025 - PRLog -- Rising sea levels are reducing the availability of habitats for migratory shorebirds along the Amazon coast, reveals a new MARE study. The research warns of the gradual transformation of tidal flats that serve as feeding areas for shorebirds during their long migrations. This phenomenon can be occurring in several regions worldwide, putting a significant number of bird species dependent on coastal wetlands at risk.

Even remote and pristine regions like the Amazon coast are not immune to human impact. Led by Carlos David Santos, a researcher from MARE - Marine and Environmental Sciences Centre, a new study published in the scientific journal Environmental Research Letters reveals that rising sea levels are profoundly transforming the coastal wetlands of the Brazilian Amazon, reducing the feeding areas available to migratory shorebirds. These birds, traveling between North and South America, depend on the extensive tidal flats to feed along their routes.

The study's authors found that the tidal flats are gradually being occupied by areas resulting from recent marine transgression. Marine transgression is caused by rising average sea level, and leads to the inland migration of coastal wetlands. The tidal flats formed by marine transgression present sediments that are too compact to be colonized by the invertebrate animals that shorebirds feed on. The research team, which includes researchers from Portugal and Brazil, used satellite images to map the distribution of tidal flats over 40 years and conducted aerial surveys to count birds along 630 km of the Amazon coast.

The results show that birds avoid the tidal flats resulting from marine transgression, where prey availability – such as small crustaceans – is significantly lower. The Semi-palmated Sandpiper (Calidris pusilla), the dominant species in the region, exhibited densities ten times lower in these areas than in older tidal flats, indicating a direct impact on their feeding.

"While the inland migration of wetlands is a positive adaptation to rising sea levels, the tidal flats created by marine transgression do not provide the necessary conditions for shorebirds to feed, at least within four decades," explains Carlos David Santos, who is also a researcher at the ARNET Associated Laboratory and the Max Planck Institute of Animal Behavior, and a professor at Nova School of Science and Technology | NOVA FCT. He adds that rising sea level is a global phenomenon and this type of habitat loss may be occurring in various regions worldwide, threatening many species of waterbirds that depend on coastal wetlands.

Published Paper: https://iopscience.iop.org/article/10.1088/1748-9326/adb444