Evidence is accumulating that migratory birds may have played a role in getting domestic fowl infected with bird flu.

Nine outbreaks of avian influenza in Northwest China's Xinjiang Uygur Autonomous Region occurred near natural wetlands. It is no coincidence as wetlands are seasonal homes for migratory birds.

In the past 50 years, wetlands in the autonomous region have decreased from 2.8 million hectares to 1.4 million. The same reduction can be seen in other parts of the country.

Human activities related to farms and fisheries have been encroaching on the territories of wild birds.

Even before the outbreaks of bird flu, experts warned the diminishing wetlands would bring about disasters for humans.

We have been caught in a trap we set ourselves.

Wetlands are a buffer zone between domestic fowl and migratory birds, according to experts. The disappearance of this natural separation means the loss of the protection belt guaranteeing harmonious co-existence for humans and wild birds.

We should remember the lessons of SARS. We killed many civet cats, which were found to be carriers of the virus causing the epidemic.

Though this particular animal carried the virus, it was the killing and eating of the cats that should be blamed.

Some migratory birds carry the H5N1 virus, which does not cause problems in itself. But if the virus is caught by chickens and ducks, the risk of human infection is greatly increased.

Statistics from the State Administration of Forestry reveal two-thirds of the nation's lakes and wetlands are polluted to differing degrees  with 20 per cent of lake water so contaminated it is no longer useable. Perhaps this degraded environment plays a role.

Ornithologist Gu Jinghe, from Xinjiang, believes the H5N1 virus has existed in the migratory population for a long time.

Much needs to be done to find out exactly how migratory birds spread the virus among domestic fowl, how humans are infected and how the virus mutates.

Nevertheless, the lessons from SARS and the outbreaks of bird flu near wetlands in Xinjiang should be enough to convince us we must take a retrospectively critical view of what we humans have done to the environment.

In recent years, efforts to preserve wetlands have been made, but they are far from enough. Statistics indicate only 40 per cent of the country's total wetland area is under protection.

Even without bird flu, human activities could not be justified if they damage wetlands, which perform a function as important to the environment as a lung is to a human.