Asian openbills: A feathered migrant reshaping Singapore parks

SINGAPORE – In 2013, a muster of six storks wowed a crowd of bird photographers in a flooded Seletar field. Unknown to many at the time, this was the first of many Asian openbills (Anastomus oscitans) to be recorded in Singapore.

Six years later, the storks began to descend on the city-state by the hundreds, becoming both a symptom and a driver of ecological changes here that scientists have yet to fully understand.

Flocks of the greyish-white waterbird were likely from Malaysia, where breeding colonies have established in Penang and Malacca.

From Lim Chu Kang to Tampines, the Asian openbill is now a familiar sight in parks, in fields and – unfortunately – on the necropsy table, with their death toll rocketing to a record high in the first five months of 2026.

Bird scientists told The Straits Times that the species, named after the gap in its beak, is likely one of the fastest-spreading avian migrants in the region. They are thriving as they feed on snails that other birds shun, and are adaptable to freshwater habitats used by humans.

In Singapore, the volume of openbill carcasses in 2026 has overwhelmed the hotline run by the Republic’s only natural history museum, marking a spike from the single digits reported in previous years.

Since January, Dr Tan Yen Yi, who conducts post-mortem examinations of the birds for the NUS Lee Kong Chian Natural History Museum, has dealt with 68 dead Asian openbills from hotline reports and animal rescue groups.

Assistant senior curator of birds Tan Yen Yi holding an Asian openbill specimen collected during the past migratory bird season from 2025 and 2026.

ST PHOTO: AZMI ATHNI

The influx makes the stork the third most common carcass of an avian migrant species reported to the museum since 2020, after the blue-winged pitta and yellow-rumped flycatcher.

“It’s really quite scary to see,” said Dr Tan, the museum’s assistant senior curator of birds. “We are struggling to cope with the storage for these specimens, so I have to pick and choose to get a good representation of the birds coming through Singapore.”

Notably, all of the dead were juveniles. Dr Tan observed that the young are more likely to die, as they are less experienced with foraging for food.

Without formal studies on the Asian openbills’ dispersal to Singapore, it is still unclear what has been propelling their journeys.

Graph on Asian openbill deaths reported.

Dr Tan said a highly successful breeding season could have pushed young birds out of their stomping grounds elsewhere, prompting them to wander to Singapore. They could also have been displaced by dry spells that hit rice fields they frequented, loss of habitat due to changes in land use, or food scarcity.

Agreeing, Bird Society of Singapore president Movin Nyanasengeran said the storks’ arrival stems from irruptive dispersal events, which occur when a population grows beyond a habitat’s capacity, or a habitat is destroyed, causing them to search for resources elsewhere.

Given the increasing number of Asian openbills recorded in Singapore annually since 2022, nearly all clustered within the winter and spring months, the society upgraded the species to a regular migrant, with the prospect of eventually becoming resident.

The influx of openbills has also been felt by the Animal Concerns Research and Education Society (ACRES). The group handled more than 130 calls about Asian openbills across the island in the first four months of 2026, a time of year when they typically get daily calls about the bird.

“Some of them are just sightings, so we have to assess whether the bird is actually injured or stranded,” said ACRES’ manager of wildlife rescue and rehabilitation Karina Lim, adding that the society responded to 20 of the cases.

These birds have actively transformed local fields and waterways. Areas once flecked with the pink eggs of invasive apple snails are being cleared out by the birds’ appetite for gastropods.

With their serrated beaks that can grip slippery shells, openbills are one of a few bird species that specialise in eating snails, said Dr Tan, who does not foresee them competing with local waterbirds for food.

At Sungei Buloh Wetland Reserve, the storks have been seen feeding on non-native snails, including the golden apple snail and African land snail, said Mr How Choon Beng, the National Parks Board’s (NParks) group director of wildlife management.

This appetite can act as a form of pest control, added Dr Movin, a bird ecologist teaching at NUS.

“Most of the freshwater species that we find in our waterways outside of the forest are not native, like the golden apple snail, so they lack natural predators,” he explained.

In fact, the openbills are a boon to farmers in Thailand, Cambodia and Laos, said conservation ecologist Yong Ding Li, who shared that Thai farmers told him they do not hunt openbills because the birds remove snails. The scientist recalled seeing grilled openbill sold in Cambodia.

Dr Yong, who manages the non-profit BirdLife International’s conservation of migratory birds in the Asia-Pacific, described the Asian openbill as one of the fastest-spreading birds in Asia, citing the species’ spread northwards from Thailand to China and southwards to Indonesia. Based on the locations where they have been sighted, he theorised that their movement arose from the birds going where snails are found. “They spread colonially in search of food. Imagine aliens invading the world – by the thousands – as they bring their friends.”

Dr Yong, who co-authored the first record of the Asian openbills here, said the continued presence of the species suggests they will likely become permanent residents in Singapore, where their population will stabilise once there are insufficient snails.

Dr Tan agreed, stating that the Asian openbills could represent the most significant change to Singapore’s avifaunal landscape, noting that many have stayed on long after migrating here.

Said Dr Yong: “It’s only a matter time (before) they will reach Java.”

Asian openbills seen at Cambodia’s Boeng Prek Lpov wetland, which non-governmental organisation BirdLife International helps to conserve, in September 2023.

PHOTO: YONG DING LI/BIRDLIFE INTERNATIONAL

While Asian openbills are susceptible to carrying avian influenza, NParks has not detected the presence of these viruses in species that have arrived here as at May 5.

As the birds become a common sight, even being memorialised in a mural at Bright Hill MRT station, scientists are warning the public to keep a respectful distance. A Facebook video in February showed children toying with a grounded openbill, which was later found by ACRES in a dehydrated state with a ruptured shoulder ligament.

Dr Tan cautioned against approaching the long-billed waterbirds, which can grow up to 81cm tall. While not violent by nature, they are known to defend themselves when they feel threatened.

“Long-billed waterbirds often stab in self-defence, and have blinded and seriously maimed people who get too close for comfort,” she warned.

Spotted an injured openbill? Contact NParks on 1800-476-160 or ACRES on 9783-7782.

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