Rising seas threaten the world’s migratory shorebirds

Birds undertake some of the world’s most impressive migrations, travelling hundreds to thousands of kilometres every year in search of safe breeding grounds and seasonally abundant food resources. For many birds, migration is the key to their success. However, migration can also make species more vulnerable to threats.

Shorebirds — species that include sandpipers, plovers and oystercatchers — live and migrate along the world’s coastlines. Over the last several decades, coastal development has led to the loss of shorebird habitats in many areas of the world, driving population declines in multiple species. Now, a new threat is emerging: climate change-driven sea-level rise.

But how exactly does sea-level rise impact shorebirds, and just how serious is this threat?

Our new study reviews the evidence from 37 published papers to provide the first comprehensive overview of the threat of sea-level rise to the world’s shorebirds. Long story short: things aren’t looking good.

Squeezing habitats out of existence

Shorebirds — as their name suggests — live along the shore, relying primarily on coastal ecosystems like beaches, salt marshes and tidal flats. As sea levels rise, these vital habitats shrink.

Some coastal ecosystems may persist in the face of sea-level rise by moving inland with the rising waters, but this isn’t always possible. More than half of the world’s largest cities are within 100 kilometres of a coast, meaning that the presence of coastal infrastructure often blocks these pathways.

This leads to a phenomenon known as coastal squeeze — where ecosystems are increasingly squeezed between the rising waters and an inland barrier (such as dikes and seawalls built to protect homes and businesses), leading to decreases in habitat.

Loss of habitat has obvious implications for migratory shorebirds: less access to food, less space for nesting and more competition with other individuals.

But habitat loss isn’t the only threat to these species. Sea-level rise may also impact shorebirds in different ways, leading to changes in prey distribution, reproductive success, feeding time and many other factors.

Just how serious is the threat?

Among the 37 studies that we examined, 21 predicted negative impacts of sea-level rise on shorebird habitats such as declines in habitat area or quality, while 17 predicted negative impacts on shorebird populations or individuals such as decreased survival or abundance.

Sea-level rise is expected to drive substantial habitat loss at many sites of international importance for migratory shorebirds. These include San Francisco Bay and Humboldt Bay in the United States, the Colorado River Delta and Marismas Nacionales in Mexico and the Yellow Sea region in East Asia, each of which supports 150,000 to more than one million shorebirds annually.

Habitat loss at these kinds of migratory bottleneck sites where large numbers of shorebirds congregate over a short period of time may hit populations particularly hard. Because so many birds funnel through these sites during migration, habitat loss in these areas may impact multiple species and entire populations. This means these sites must be a priority for conservation.

Balancing the needs of humans and wildlife

Maintaining coastal ecosystems and protecting them from the threat of sea-level rise will be essential for the survival of thriving shorebird populations. But coastal ecosystems aren’t only important for shorebirds. They also support thousands of other species and provide valuable ecosystem services such as coastal protection, water filtration and carbon storage.

In order to preserve these habitats and the species that depend on them, governments will need to make a serious effort to mitigate the impacts of coastal squeeze. Rather than continuing to armour our shorelines, decision makers should prioritize solutions that will protect human communities while also benefitting coastal ecosystems.

The shape that these actions take may vary from place to place. In some areas, it may be necessary to relocate coastal infrastructure to give ecosystems space to move inland as sea levels rise — an approach referred to as “managed retreat.” In other areas, scientists and practitioners are looking at how we can use sediment recovered from dredging to enhance or create new habitats.

However we choose to respond to sea-level rise, urgent action will be required to preserve shorebirds and their fascinating migrations for generations to come.