By Yu Nan (China Daily)
Updated: 2004-02-10 11:10

People generally used to pay little if any attention to the millions of migratory birds in East Asia on their twice-annual pilgrimages between New Zealand and Siberia.

However, since avian influenza, or bird flu, has taken hold in the region, some scientists are suggesting that migrating birds may be responsible for carrying and introducing the virus to various parts of Asia, including China.

They advise that people should be aware of this possibility and, therefore, avoid any sort of contact with migratory birds.

"We are keeping a close watch for any changes in flight patterns or behaviour of migratory birds, but not in an invasive way," Liu Binsheng, deputy director of the zone administration of Poyang Lake, in East China's Jiangxi Province, told China Daily.

The largest freshwater lake in China, with an area of 22,400 hectares, Poyang Lake is a major stopping point for migratory birds passing through China, including white cranes, wild geese and dozens of others species.

The estimated number of sightings in 2002 totalled 350,000, according to Liu.

Researchers have found that some rare species of migratory birds, such as the red-crowned crane and Oriental white stork, start to fly to cooler areas in north and northeast Asia in March.

"So far the behaviour of the birds in their natural habitat on and around the lake seems to be normal," he said. "But we suggest that local people do not raise their ducks on the lake to prevent a possible cross-infection."

"But we are being careful not to disturb the lives of the birds here on Poyang Lake," he said.

Nonetheless, he is still a little concerned about the reports that migratory birds may be carriers of the H5N1 virus, he said.

According to information given on the World Health Organization website, migratory birds, including wild waterfowl, sea birds, and shore birds, can carry the virus for long distances.

Such birds have, in the past, been carriers in the international spread of highly pathogenic avian influenza, although these birds themselves are also the most resistant to infection.

They can excrete the virus in their droppings, yet develop only a mild and short-lived illness.

"They have probably played a central role in spreading the disease, with their droppings infecting the waters where they live, or drying up and turning to dust that may be inhaled by other birds, including domestic ducks and chickens" said Zhou Jiao, a professor of zoology and veterinary science with the Beijing Academy of Agriculture and Forestry.

But some people believe such a perception has made migratory birds the scapegoats for the present avian infuenza outbreaks. They have strong reservations about the hypothesis.

"It is highly unlikely they have brought the virus in," said Zhong Jia, a newspaper reporter and a keen bird watcher, who has just returned to Beijing from an investigative trip to check the migratory birds in the Yangtze River valley.

"The most important reason is that the wild birds are seldom, or never, in contact with domestic poultry even when they inhabit the same waters, according to my long-time bird-watching experience across the country," she said.

"And if poultry is raised in the same waters, the wild birds usually look for other places to rest and find food."

"The timing also doesn't match," Zhong added. "Migrating birds usually sojourn at their stop-off points in January and February and start to flock northwards in March, but the virus began to spread in early January."

Chu Guozhong, a noted expert in ornithology and director of the China Bird Banding Centre, agrees that the risk factor among wild birds is low.

"Migratory birds have their special living habits. They always choose stop-offs as far away as possible from humans," Chu explains. "There is no need to be scared of the migratory birds."

Zhong said she was glad to learn that the staff of the Huairou Reservoir in Beijing, has prepared supplies of millet along the riverbank for migratory birds.

Huairou Reservoir, in the northern environs of Beijing, is a major stop-off for around 100 species of migratory birds.

"There is no need for people to fear migratory birds," she said.

In addition to food preparation, the reservoir also sends people to patrol the areas around nearby villages every day to monitor the condition of domestic chickens and ducks.

Now, WHO experts and research centres throughout Asia are studying whether the flu outbreaks in Viet Nam, South Korea and Japan as well as in China's Taiwan Province may have been introduced by wild migratory birds.

The researchers have coined a phrase, the "East Asian Flyway." It is like a huge aerial motorway along which wading birds, songbirds and other winged wanderers flock south in the winter and north in the summer. It has become a major area for investigative research, according to Chu.

The most popular rest areas along the flyway include the marshes of northern Hong Kong, the cool volcanic lakes of Luzon in the Philippines and the lowlands of the southern Korean Peninsula, he said.