Migration routes are complex but can take wildfowl from Asia to Russia where they come into contact with others that then fly south across eastern and central Europe to Africa.

"The surveillance during the summer has shown governments are alert and there is now a lot of collaboration with wildlife bodies and industry," Alex Thiermann, head of the standard-setting committee of the Paris-based World Animal Health Organisation (OIE), told Reuters.

"The monitoring of wildlife is more intense than it was in the spring. So, if something was to happen, we should be better prepared to know about it sooner," he added.

While experts believe trade in poultry has played a role in international transmission of bird flu, wild birds can carry the virus long distances. But they note there hasn't been widespread detection of H5N1 in Russia this summer compared with levels seen in 2005.

"Awareness is higher, but the risk of the virus in wildlife is lower, based on what we've seen this summer," Thiermann said.

The H5N1 virus is still primarily a poultry disease but has killed 146 people since 2003, mostly in Asia. Some 200 million birds have either died or been culled to control its spread.

Scientists fear that H5N1 could mutate into a form easily spread between humans, sparking a worldwide pandemic and killing millions of people. The World Bank has warned a severe human pandemic could cost the global economy up to $2 trillion.

ALERT

Most European Union countries have relaxed measures requiring poultry to be kept indoors but authorities are ready to revive the order should risk levels increase.

"In view of the forthcoming migratory season of wild birds, there is a continued need for the highest levels of vigilance," the European Commission said.

"Member states are therefore urged to keep appropriate biosecurity measures, early detection systems and rigorous import controls in place," it said.

In Germany, the lock-up order remains in force, but large numbers of exemption permits have been issued during the period of low risk, allowing extensive free-range farming.

And in Britain, the government has launched a new strategy of testing birds more intensively in areas where an outbreak is more likely to occur.

Some 14 EU states that have detected H5N1 -- Greece, Italy, Slovenia, Austria, Germany, Hungary, Britain, France, Slovakia, Sweden, Poland, Denmark, the Czech Republic and Spain.

But no cases have been reported since Spain in late June.

COHERENT MESSAGE

The spread of bird flu from Russia to Turkey and Romania and then into the European Union last winter triggered consumer panic, with poultry sales plunging as much as 50 percent in Italy and up to 30 percent in France. Many countries banned imports from disease-hit regions.

The crisis cost farmers millions of dollars, hit shares of major meat producers and sparked calls for compensation.

"The question is how do we minimise the adverse reaction. If there is a dead duck in the wild, we need to make sure there's not that negative impact on consumption," Thiermann said.

Bird flu can be passed to humans that have had sustained close contact with diseased animals, but experts say there is no danger from eating properly cooked meat.

Thiermann said information needed to be coordinated.

"The message has to be a single one. The communication has to be coordinated between public health and animal health authorities and the people in wildlife groups," he said.