For some, the heron is a symbol of beauty in a city far better known for its gleaming skyscrapers, towering apartment blocks and crowded city streets.

For others, wild migrating birds are carriers of death.

A grey heron infected with bird flu was found dead near the reserve this month, reigniting fears about the ability of wild birds to spread a disease that has killed 32 people in Asia this year and wiped out millions of poultry.

In recent years, people have come to identify wild birds as a natural host of the deadly H5N1 bird flu virus, which scientists have warned could spark the world's next flu pandemic, killing thousands, possibly millions, of people.

But Hong Kong experts are reassessing the role of wild birds, and say they may be getting a bad name they don't deserve.

Experts say certain wild birds are natural carriers of the disease and still pose a risk to the rest of the world. But the H5N1 strain has become so endemic in poultry farms in Asia that migratory birds are no longer an important factor.

The H5N1 strain swept through much of Asia this year, wiping out poultry populations and killing 32 people in Thailand and Vietnam. Where sources of infection could be traced, victims were invariably linked to infected poultry, not wild birds.

WIDESPREAD

"In reality now, part of the transmission that's going on is lateral transmission on the ground. People walking around, holding cages (of infected birds), or infected poultry coming into bird markets and going to other parts of the world, that's the kind of spread that's occurring," said Malik Peiris, a leading microbiologist at the University of Hong Kong.

"The H5N1 has really got a foothold in Asia. It's so widespread we don't need migratory birds to spread it further."

Lew Young, manager of the Mai Po reserve, agrees.

"The fact that there were H5N1 outbreaks throughout this summer in Southeast Asia, which is outside the season for migratory birds to be moving, means it is more likely that the virus is already endemic within the poultry population and it doesn't need wild birds to bring the virus down to southern Asia any more."

Of the 2,000 stool and blood samples taken this year from wild birds in Hong Kong, only two were found with the H5N1.

"If there is a risk of an epidemic worldwide, it will probably not be due to wild birds," Young said.

The 1,500-hectare (3,750 acre) Mai Po sanctuary is a key resting stop for more than 300 species of wild birds fleeing bitter winters in their breeding grounds in northern China, Mongolia and Siberia to warmer grounds in Southeast Asia and Australia.

Experts stress the importance of protecting domestic flocks from wild birds, though even they say that is very difficult.

"Because certain wild birds may be carriers of H5N1, there is always a certain risk that the virus may be transmitted to domestic poultry," Young said.

"Putting screens over chicken coops may be one way of reducing the risk. But in many parts of Asia, poultry may not always be in a coop. They may be free range, particularly in China, Southeast Asia, so it is difficult to control."

IMPOSSIBLE TO ELIMINATE

Although governments in the region have slaughtered tens of millions of birds in a bid to contain the flu strain, it has proven to be extremely hardy and has re-emerged several times.

"We have something that is geographically so widespread that ... it will not be possible to eliminate it," said Peiris.

The SARS and bird flu viruses originate from animals, which act as carriers and usually don't display symptoms of the disease. But H5N1 bird flu is far deadlier in humans and kills up to a third of all its victims.

It was first seen in humans in Hong Kong in 1997, when it killed six people. No one knows how it jumped from birds to man. Scientists suspect there were human-to-human transmissions in Hong Kong and Thailand, but these have never been confirmed.

The scientific community fears that given enough time, the bird flu virus will evolve to jump from human to human, in much the same way that the SARS virus did in 2003.

Casting a wary eye on the lethal H5N1, the World Health Organisation urged governments this month to provide funds to drug makers developing vaccines against a feared flu pandemic.

Scientists say major flu pandemics occur every 30 to 35 years. The deadliest in the past century was the Spanish Flu pandemic of 1918-19 that killed between 20 million and 50 million people worldwide. The exact source of this virulent strain is unknown but is thought to have been wild birds.

The virus behind the last major flu outbreak, the Hong Kong Flu pandemic of 1968, is thought to have originated in wild aquatic birds such as ducks.

With SARS and the H5N1 discovered first in southern China, Beijing is understandably worried. It recently approved a plan to build a state laboratory in Hong Kong, the first in China to study emerging infectious diseases.

"So many pathogens were first identified in Hong Kong because Hong Kong and southern China have the highest density of ... humans and animals. They live in close proximity to each other," said Yuen Kwok-yung, a top microbiologist in Hong Kong.

"We have a unique eating culture, we like fresh meat, sell live poultry in markets, all these predispose us to be a very important sentinel post for the study of infectious diseases."