A version of this article appeared in The Straits Times on May 12, 2012.

SINGAPORE - THE curlew sandpiper - a small, common wading bird - flies vast distances from Arctic Siberia to get to Singapore, and sometimes journeys on to spend the northern winter in Australia.

But it is getting here a day later in the year than it did three decades ago, which could signal it is changing its migration patterns as temperatures rise up north.

That is cause for concern, said birdwatcher and junior college lecturer Yong Ding Li, who is studying such migration patterns using data from Singapore birders.

Mr Yong, 28, remarked that the timing of migratory birds' arrivals from and departures for their tundra breeding sites indicates how likely the species is to be threatened by climate change.

"If they don't reach their breeding sites on time, food might not be plentiful and survival rates may be lower," he said.

That wreaks havoc on the birds' breeding cycle, which depends on both internal biology and the external environment.

In Europe, some waterfowl species are setting off as much as a month late, Finnish researchers have found from 30 years of data.

Migratory birds are also threatened by habitat loss farther north, especially in East Asia's fast-developing coastal regions, Mr Yong said.

Here, generations of birders have enjoyed spotting foreign avian visitors at sites like Sungei Buloh Wetland Reserve, mudflats at Mandai and even parks and gardens.

A third of Singapore's more than 300 recorded bird species are migrants.

The island state is a pit stop along the East Asian-Australasian Flyway, the migratory pathway from eastern Russia to New Zealand.

It may not host as many birds as other countries, where feeding and roosting grounds are much larger, but there are occasional surprises, said Mr Alan Owyong, 66, of the Nature Society's Bird Group.

In 2008, a Nordmann's greenshank, a rare wader, showed up at Sungei Buloh 27 years after the last one was sighted here.

And early last year, a common redshank which was tagged with an ankle ring here 20 years ago was spotted - a record for an individual bird, said Mr Wong Tuan Wah, director of conservation at the National Parks Board.

A number of events will be held today at Sungei Buloh Wetland Reserve to mark World Migratory Bird Day.

They include Migratory Bird Day talks at 9.30am and 11.30am, guided walks at 9am, 10am and 11am, and a talk by National University of Singapore geography researcher Dan Friess about Singapore's mangroves at 10.30am.