As bird flu hit this and other Asian countries and Europe, people worried that migratory birds might spread the deadly virus.

The Food and Agriculture Organization of the United Nations warns on its website that "there is a potential risk that HPAI subtype H5N1 might be carried along migration routes of wild water birds to densely populated areas of the south Asian subcontinent and along migratory flyways to Africa and Europe."

Leading Chinese veterinarians also sounded alarms that wild birds including migratory birds have been found carrying the virus, although the experts haven't provided the public with details.

But a leading expert on the birds of Southeast and East Asia recently pointed out that migratory wild birds are victims, rather than vectors of the highly pathogenic H5N1 strain of avian influenza.

"Migratory birds can be vectors, but evidence indicates this is very rare and they are more often victims of HP H5N1," Colin Poole, Asia programme director of the international Wildlife Conservation Society (WCS), based in the US, told China Daily last week at a Beijing symposium.

The November 15-17 symposium, "One World One Health. The Threat of Emerging Disease to Human Health, Agriculture and Conservation: Implications for Policy," was co-organized by WSC and the Zoology Institute of the Chinese Academy of Sciences.

British scientist Poole, a former chairman of the Oriental Bird Club, a non-governmental organization based in Britain, says data collected by many people shows that the majority of H5N1 infected birds have been resident, not migratory.

In most cases, infected wild birds lived near poultry farms.

And migration routes of wild birds didn't match patterns of bird flu occurrence.

"If you look at the outbreaks of bird flu, where they happened and what time," he said, "it doesn't fit with our understanding of how wild birds migrate, where they migrate from, and where they migrate to."

He cited Northwest China's Qinghai Province as an example.

In late May, over 6,000 wild birds were killed by HP H5N1 bird flu around Qinghai Lake.

The infected birds were mainly great black-headed gulls (Larus ichthyaetus), brown-headed gulls (Larus brunnicephalus), and bar-headed geese (Anser indicus).

After breeding at Qinghai Lake, these birds migrate in autumn to southern China, India and Bangladesh. They do not migrate west to Russia, Kazakhstan or Europe.

If the birds were carrying bird flu, there would be reports of dead wild birds in northern India, Bangladesh, or other places south of Qinghai Lake.

But there is no such report. "To me, this is strange," he said. "If the birds are carrying it, why aren't they carrying it south when they winter."

He's seen the map some people draw of birds migrating west from Qinghai to Europe. "But I don't think these species do that," he said. "Something else must be causing the outbreaks in Europe, not migratory birds."

Of eight major global migration routes, three pass through Asia. They are the Central Asian-Indian Flyway, East Asian-Australian Flyway and West Pacific Flyway.

Poole says the three merge into one. Birds generally migrate from north to south, though there are almost as many migration routes as there are species of migratory waterbirds.

"If we talk about bird migration, we must identify the species, as every species migrates in different ways, to different places, at different times," he said.

So how prevalent is HP H5N1 in migratory wild birds? Though figures are hard to come by, the ornithologist still managed to find:

Over the last two years over 100,000 wild birds have been tested across the region. And now any dead bird found almost anywhere is tested. Yet only a few hundred have tested positive for HP H5N1.

The great majority of infected wild birds have been resident species like crow, magpie and sparrow that are ecologically linked to poultry.

The Mai Po Nature Reserve in Hong Kong has tested samples of bird excrement since the first outbreak of avian flu in 1997. None of 4,000 to 7,000 samples taken annually has tested positive for H5N1.

In Mongolia, over 850 faecal samples were collected from wild birds in August 2005. Only one tested positive for HP H5N1.

However, a study last year of domestic ducks in the Vietnamese Mekong Delta showed that over 70 per cent tested serologically positive for H5N1.

Conservationist Poole says the real problem is the "migration" of birds in trade.

Eight of 46 birds tested in a shipment of 1,037 being smuggled by ship along with "a number of mice and turtles" to Taipei were positive for H5N1. Species included Hill Myna, Black-naped Oriole and Red-billed Leiothrix.

A parrot brought into the UK as part of a mixed consignment of 148 parrots from Surinam (South America) was held in "quarantine" with 216 birds from China's island province of Taiwan before dying of H5N1 after 30 days.

In October, 2004, two Mountain Hawk Eagles smuggled by commercial plane from Thailand to Belgium were tested positive for HP H5N1. "They think the birds got the virus because they were fed with infected chickens in Thailand," Poole said.

He said, there are some things "we cannot do" and a few things "we can do."

"We can't eliminate birds with forms of avian influenza in wild populations," he said. "We can't stop birds migrating.

"There's no point culling wild birds it just causes them to disperse further."

But people can do a better job of separating wild and domestic birds, get better control of the bird trade and live markets, and increase the bio-security of free range poultry farming and waste products.

"And we need to better understand and monitor wild bird movements and ecology, so we can assess the real risk areas," he said. "We know little about the migratory birds in Asia. We need better data.

"So don't blame migratory birds. If we blame them, we will fail to address the real problem."

(China Daily 11/24/2005 page13)