Millions of shorebirds could be lost as sea levels rise
in the coming decades, international environmental scientists have
warned.
World-first research predicts that a loss of 23 to 40
per cent of the birds’ main feeding grounds could lead to a 70 per cent decline
in their population.
This places some of the world’s shorebirds at greater
risk as some areas have already reported alarming population losses of 30-80 per
cent.
“Each year, millions of shorebirds stop at coastal
wetlands to rest and feed as they migrate from Russia and Alaska to the coasts
of Southeast Asia and Australasia,” says Dr Richard Fuller of the National
Environmental Research Program’s (NERP) Environmental Decisions Hub and The
University of Queensland (UQ).
“We’ve discovered that some of these wetlands are
highly vulnerable to sea level rise and might be lost in the next few decades.
If the birds can no longer stop at these areas to ‘refuel’, they may not be able
to complete the journey to their breeding grounds.”
The NERP researchers studied wetlands along the
shorebirds’ migration route across coastal Alaska, Russia, China, North Korea,
South Korea, Japan, Philippines, Vietnam, Thailand, Malaysia, Indonesia, Papua
New Guinea, Australia and New Zealand.
In many cases rapid coastal development and reclamation
are already chewing into the tidal wetlands the birds use as feeding grounds on
their long journeys, which sometimes extend halfway round the world. Species
already showing signs of being in trouble include the bar-tailed godwit, curlew
sandpiper, eastern curlew, great knot, grey-tailed tattler, lesser sand plover,
red knot and terek sandpiper.
The scientists used “graph theory”, a mathematical
approach to estimate the impact of the loss of these wetlands on
shorebirds.
“We found that if a tidal wetland habitat serves as an
important ‘stepping stone’ for the shorebirds, a small amount of habitat loss
can trigger disproportionally large declines in the population,” says Dr Takuya
Iwamura of Stanford University, who conducted the research at NERP. “This is
because some of these tidal wetlands are ‘bottleneck’ sites where the majority
of the birds stop to refuel.
“For example, we discovered that a sea level rise of
150 centimetres may result in the loss of 35 per cent of coastal wetlands, but
it could lead to a 60 per cent decline in curlew sandpipers, eastern curlews and
great knots.”
NERP scientists are also embarking on a second
international study to identify the best ways to save the disappearing
shorebirds. This research is crucial for federal policy because Australia has
signed migratory bird agreements with China, Japan and South Korea.
“We’re aware that some shorebird species have declined
in the past few decades, but we still know very little about all the causes for
these declines or the scale of the problem,” says Mr Rob Clemens of NERP and
UQ.
“Our studies attempt to piece together what is
happening throughout the entire migration journey of these birds,” he says. “We
can then determine which species should be protected, how best we can monitor
the birds, and where and how we should act to save them.
“But while more knowledge would be useful, it’s
important that we start protecting the birds based on what we already know, such
as halting the reclamation of coastal wetlands in the vulnerable
regions.”
Dr Richard Fuller explains that huge areas of the
world’s coastal wetlands have been reclaimed for urbanisation and agriculture in
recent years, reducing the size of the wetlands available for migratory
birds.
While some existing wetlands can shift inland as sea
levels rise, sites along highly developed coastlines, for example in Japan,
China and the Republic of Korea, cannot move at all because of the scale of
human development close to the coast.
“While we can build sea walls to defend ourselves
against rising sea levels, the cost of this will only increase as time goes by,”
Dr Fuller says. “We could instead be looking for opportunities to return our
coastlines to a more natural state.
“We must act now to protect these crucial ‘stepping
stones’ for migratory shorebirds – if you lose one critical site, you risk
losing the entire population of a species that stops there.”
The
study “Migratory
connectivity magnifies the consequences of habitat loss from sea-level rise for
shorebird populations” by Takuya Iwamura, Hugh P. Possingham, Iadine Chadès,
Clive Minton, Nicholas J. Murray, Danny I. Rogers, Eric Treml and Richard A.
Fuller appears in the latest issue of Proceedings of The Royal Society
B.
