Science1 publisherNot yet confirmed elsewhere2 min readPublished
Most of 37 sea-level studies forecast habitat loss for migratory shorebirds
Shorebird researchers reviewed 37 published studies and found 21 that predict rising seas will shrink or degrade the birds' coastal habitat. They trace much of that loss to coastal squeeze, where dikes and seawalls stop beaches and marshes from retreating inland as the water rises.
The Scientist · Science desk
What happened
- Seventeen of the reviewed studies predicted harm to the birds themselves, such as lower survival or smaller numbers, in addition to the habitat forecasts.
- Coastal development had already removed shorebird habitat in many regions over several decades, driving declines in multiple species before sea-level rise emerged as a threat.
- Projected losses include San Francisco Bay, Humboldt Bay, the Colorado River Delta, Marismas Nacionales and the Yellow Sea, each used by 150,000 to over 1 million shorebirds a year.
- Beyond lost area, the reviewed work points to sea-level rise changing where prey is found, how well birds breed and how long they can feed.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- decision Each new dike or seawall is a habitat decision as well as a flood decision, and the authors want governments to favor defenses that protect people and coastal ecosystems together.
- exposure A loss at one migration bottleneck can reach several species and whole populations at once, because large numbers of birds pass through these sites in a short period.
- cost Managed retreat, one of the authors' proposed responses, asks coastal communities to relocate infrastructure, so the price of keeping habitat falls on the land and buildings behind the shore.
Start with the denominator. The 21 habitat forecasts and the 17 forecasts of harm to birds add up to 38. That is one more than the 37 papers reviewed, so at least one paper falls in both groups [16]. As shares, 57% of the papers project worse habitat and 46% project lower survival or abundance [17][18]. Both counts are predicted impacts, not measured declines [2][3]. The authors' summary does not say what the remaining papers found or how large the projected losses are.
The authors wrote about their own review on phys.org and describe it as the first comprehensive overview of the threat sea-level rise poses to the world's shorebirds [1]. "Long story short: things aren't looking good," they wrote [15].
A rising sea does not automatically erase a coastal habitat. Some beaches, salt marshes and tidal flats can survive by moving inland as the water climbs, though the authors note this is not always possible [14]. More than half of the world's largest cities lie within 100 kilometers of a coast, and the infrastructure around them often blocks those inland routes [5]. In the authors' account, the habitat caught between rising water and a fixed barrier gets narrower [6].
The two threats are hard to separate. Development removed shorebird habitat for decades, and the dikes and seawalls built to protect homes and businesses are what turn rising water into further loss [4][6]. Any one population decline will probably have both causes, and the review's tally of studies does not split them.
The authors also describe a way to add habitat. Researchers are testing whether sediment recovered from dredging can improve existing habitat or create new habitat [10]. The same coastal ecosystems support thousands of other species and provide coastal protection, water filtration and carbon storage [13].
I think the tally is enough to support the authors' call to protect the bottleneck sites first [8]. Working out how much any one site will lose will take local modelling of how much habitat the water and the walls leave behind.
What to watch
- Site-level models for San Francisco Bay or the Yellow Sea that put hectares or bird counts on the projected habitat loss.
- Flood-defense plans at the named bottleneck sites, and whether they choose managed retreat or new seawalls.
- Results from trials using dredged sediment to raise or create tidal flats and marshes for shorebirds.