BANGKOK, Thailand - Nearly half of the world's waterbird species are in decline, mostly due to rapid economic development and the effects of climate change, according to a global survey released yesterday.

The fourth Waterbird Population Estimate found that 44 percent of the 900 species globally have fallen in the last five years, while 34 percent were stable, and 17 percent rising.

Altogether, 12 families of birds have half or more of their global populations showing a decreasing trend, including storks, shoebills and plovers.

The numbers are slightly worse than 2002, when the last study was conducted. At that time, 41 percent of waterbird populations worldwide were found to be decreasing.

The worst decreases occurred in Asia, where 62 percent of the waterbird populations had declined or become extinct. That was followed by a 48 percent decline in Africa, 45 percent in Oceania, 42 percent in South America, 41 percent in Europe, and 37 percent in North America.

Simon Delany, a waterbird conservation officer for the Netherlands-based Wetlands International, which coordinated the survey, said the cause of the decline was a loss of wetlands either from economic and agriculture development or rising temperatures, which are blamed for worsening droughts and rising sea levels.

The survey represents about 50,000 hours of fieldwork in 100 countries.

"Human impacts such as urban sprawl, reclamation of wetlands, increase of pollution, and hunting pressure can develop rapidly, and conservation considerations are often not taken into account," Delany said.

Darters, screamers, rails, finfoots, jacanas, painted-snipes, stone curlews, seedsnipes and skimmers were other species that have gone into decline, the report said.

In North America, the king rail population was found to be declining, while the American white pelican populations rose.

Delany said the threats are wespecially visible in Asia, where mangroves are being destroyed to make way for shrimp and fish farms, and wetlands are increasingly being reclaimed for industrial estates and tourist resorts.

South Korea, for example, has converted about half the country's 988,400 acres of tidal flats for commercial purposes while China has taken half its mangrove forests since 1949 for land reclamation and aquaculture.

"Land reclamation is simply removing huge areas of wetlands, which means very large numbers of birds and other species have nowhere to live," Delany said. "Many of these birds are long-distance migrants, so they need these places to feed."

Delany and others said there were positive developments in the survey, especially in Europe and North America, where most bird populations are either stable or on the rise.

He attributed that to stabilizing human populations as well as a greater environmental awareness that has led to stronger regulations and greater protection of wetlands.