SINGAPORE - Far fewer migratory birds fleeing harsh winter environments have made a stop in Singapore over the years, partly because of threats that had been less well studied until now - hunters, anti-bird nets and fishing nets in China, as well as in South-east Asia.

At Sungei Buloh Wetland Reserve, ornithologist Yong Ding Li has noticed a drastic decline in a few voyaging shorebird species - such as the curlew and marsh sandpipers - between the 1990s and now.

"In 1994 and 1995, I would easily count 200 to 400 Arctic-born curlew sandpipers yearly, but nowadays, to see a small group of three to five would be rare," said Dr Yong, head of flyways and species conservation for Asia at non-governmental organisation BirdLife International.

While the decline in the number of migratory birds is largely attributed to habitat loss and climate change, scientists have recently confirmed the worrying threats of hunters, anti-bird nets and fishing nets in China.

Researchers estimate that more than 47,800 birds were killed each year in 19 stopover sites along China's coasts where the feathered travellers stop to refuel during their great migration to escape the harsh winter.

After surveying those sites, the researchers analysed the number of birds trapped in the nets using a series of statistical models to estimate the death toll, and to what extent these losses affect the overall populations of each species.

Their findings were published in scientific journal Nature Ecology & Evolution on Sept 9.

Anti-bird netting over razor clam farms were responsible for more than 60 per cent of the deaths in 39 species, said ecology and evolutionary biology expert David Wilcove from Princeton University, who oversaw the research.

He said the three threats were less studied previously because more research was done on the loss of intertidal habitats to development.

"That's an important thing to do because... without adequate habitat to rest and refuel, the shorebirds cannot complete their migration.

"Thus, the other threats these shorebirds face, such as direct human-caused mortality, did not get much attention until now," Professor Wilcove, who is also vice-dean of the Princeton School of Public and International Affairs, told The Straits Times.

For 11 of the affected species, the death toll from hunting and being entangled in nets accounted for more than 1 per cent of their migrating population. That is more concerning for species already under conservation threat, said the paper.

The figure was 1.21 per cent for the curlew sandpiper and close to 10 per cent for the terek sandpiper, which also makes a pit stop at Singapore's wetlands, shores and marshes.

The species most heavily impacted by anti-bird nets, hunting and fishing nets are the terek sandpiper, vulnerable broad-billed sandpiper, little ringed plover and long-toed stint, said Prof Wilcove.

The presence of these species in Singapore is "quite rare these days", said Dr Yong, who was not involved in the research.

He also noted that nets used for hunting and deterring birds have been widely documented in South-east Asia, especially in Vietnam, Thailand and Indonesia.

Other declining species that Prof Wilcove highlighted are the endangered far eastern curlews and great knot, which have been spotted in the Republic in the past.

Only about 20,000 far eastern curlews, one of the largest shorebirds in the world, may survive as they are threatened by habitat loss and hunting.

"The great knot population is much larger, at around 400,000, but the species is declining at a very steep rate. It is threatened, again, by habitat loss, hunting, bycatch and capture in bird deterrence nets," said Prof Wilcove.

It is currently the beginning of the migration season, and massive flocks are escaping their chilly breeding grounds in the north for their annual southern voyage.

Between August and March, shorebirds can be seen foraging in hot spots including Sungei Buloh, Mandai mudflat, Chek Jawa and Marina East Drive.

Singapore and China's coasts are key stopover points along the East Asian-Australasian Flyway that stretches from the Russian Far East and Alaska, southwards to East Asia and South-east Asia, and even to Australia and New Zealand. This is the world's largest migratory bird highway spanning more than 30 countries, and is used by 600 species of birds. It is home to over 50 million migratory waterbirds.

The study's researchers surveyed 29 stopover sites from southern China to the north-eastern region in the autumn of 2019 and spring of 2021. At 19 of the sites, nets, along with entangled and caged birds, were spotted. In the spring of 2023, they surveyed an additional 34 sites.

Since bird deterrence nets are responsible for most of the deaths, Prof Wilcove said farms should remove the nets after razor clams are harvested in late March and early April.

"This is before the peak of the spring migration. This simple step would save most of the shorebirds," he added.

"We should also be looking at other ways besides nets to deter shorebirds from foraging in the tidal flats where the razor clams are being grown."

Nets, many of which are clear or green, do not appear to be visible to the birds when they swoop down to make landfall and hence get entangled.

If nets are used, those with larger mesh sizes should be used, with visible flags or ribbons attached. But it is difficult to ensure the nets are visible both day and night, Prof Wilcove noted.

Government leaders should consider creating incentives or a commercial insurance programme for farmers who agree to forgo anti-bird nets, the paper stated.

Prof Wilcove added: "Hunting of shorebirds is illegal in most of the countries along the flyway, so what's needed is greater enforcement, combined with more intensive monitoring of the less well-known stopover sites."

BirdLife International's Dr Yong said the Chinese authorities and local organisations have taken steps to stem the use of mist nets, which trap birds and bats. For example, shopping platforms restrict the sale of such nets.

"The use of mist nets for hunting has declined in several areas, and there are regular enforcement operations against their use during the migration season," he added.

Source: The Straits Times © SPH Media Limited. Permission required for reproduction