At low tide the mudflats of Sungai Buloh stretch a kilometre out toward the Strait of Malacca, slick and dark and dimpled with the breathing holes of mudskippers. Just before dawn the first grey heron lifts from a roost in the mangroves and flies, slow and deliberate, out to the tideline.

Nurul Aisyah Hassan watches it from the observation tower at the edge of the reserve. She is forty-three, a senior research officer with the Malaysian Nature Society, and she has counted the herons of Sungai Buloh every other Saturday since January 2015.

The reserve sits on the Selangor coast, about thirty kilometres northwest of Kuala Lumpur. From the tower one can see, on a clear morning, the tops of the Petronas Towers fifty kilometres inland. The proximity is the point. Sungai Buloh is one of the last large coastal wetlands within commuting distance of a major Southeast Asian capital.

It survives by a combination of accident and intention. The accident was that the land was difficult to develop. The intention was a 1989 decision by the Selangor state government to gazette four hundred hectares of mangrove and mudflat as a permanent forest reserve.

Hassan's count this morning, by 7:30, stands at 142 grey herons, Ardea cinerea, 38 great egrets, 11 striated herons, and, most importantly, three milky storks.

The milky stork, Mycteria cinerea, is the reason her count matters internationally. The species is classified as endangered by the IUCN, with a global wild population estimated at fewer than 1,500 mature individuals. The Malaysian population, centred on the Selangor coast, is perhaps the most accessible and best studied subpopulation in the world.

Hassan's data, deposited annually with the Asian Waterbird Census, shows the local milky stork count declining from a peak of 27 individuals in 2017 to a low of 6 in 2022, and recovering slightly to between 9 and 12 in the most recent surveys.

The reasons for the decline are not mysterious. Aquaculture ponds have replaced mangrove along much of the Selangor coast outside the reserve. Plastic pollution accumulates in the tideline. A captive-breeding programme at Zoo Negara in the 1990s and 2000s released birds that hybridised with painted storks, complicating the genetic picture.

“The reasons for the decline are not mysterious.”

Dr. Yeap Chin Aik, an ornithologist with the Malaysian Nature Society and Hassan's longtime collaborator, has argued in a 2023 paper in Bird Conservation International that the future of the milky stork in Malaysia depends entirely on protecting a small number of coastal wetlands. Sungai Buloh is one. The Kuala Gula Bird Sanctuary in Perak is another.

Hassan does not disagree, but she is more interested in the herons themselves than in the policy.

She knows individual birds by subtle differences in plumage. There is a grey heron she calls Patah, named for a broken outer primary feather on its left wing, that she first ringed in 2018 and has resighted on the same mudflat fifty-one times since.

She knows where the great egrets prefer to feed at neap tide. She knows which channel in the mangrove holds the largest roost of black-crowned night herons. She knows that the milky storks tend to arrive at the reserve in the second week of November and leave in late March, and she does not know where they go in between.

A telemetry study, run by the Department of Wildlife and National Parks in partnership with the University of Putra Malaysia, has fitted three milky storks with satellite tags since 2024. The data so far suggests they move between Sungai Buloh, the Klang Islands, and an estuary on the Sumatran coast near Bagansiapiapi.

Hassan finds this both fascinating and worrying. The corridor crosses one of the busiest shipping lanes in the world.

She works alone most weekends. Her husband, a teacher, sometimes drives out with their two daughters and a flask of coffee. The girls have learned to whisper.

The reserve has a small visitor centre and a network of boardwalks. On a busy weekend perhaps eighty people visit. Most are urban families curious about the birds. Hassan has noticed, over a decade, a slow increase in interest. The Malaysian birding community is larger now than it was. Schools bring children. A retired civil servant from Petaling Jaya has begun submitting his own counts to eBird.

She thinks this matters in ways that are hard to quantify. A wetland with witnesses is harder to lose.

The threats, however, are real and continuing. A 2024 proposal to widen the coastal highway would have removed thirty hectares of buffer mangrove on the reserve's eastern boundary. The proposal was withdrawn after public opposition, much of it organised through the Malaysian Nature Society. A revised version is expected.

By late morning the tide has begun to turn. The herons fly in, one by one, from the outer flats to the mangrove edge. Hassan packs away her scope. She has logged 187 individual sightings, two new ring resightings, and one apparent injury, a great egret with a fishing line tangled around its right tarsus.

She will call the wildlife rescue team on the drive home.

Out on the strait a container ship the size of a small town moves slowly south. Inland, Kuala Lumpur stirs. The grey herons stand in the shallows, motionless, and wait.