The team tags birds with solar-powered GPRS microchips and a US satellite receiving station then tracks their flight paths.

The Mahidol idea won funding from the US Centres for Disease Control in October last year.

The team includes experts from Siriraj Hospital medical school, Mahidol's veterinary and science faculties, the Public Health Ministry's disease control and medical sciences departments and an American research company.

Over the past 30 years birds migrating to Vietnam via Thailand came from Bangladesh and India. However, the ecology has changed, Siriraj virologist Prof Pilaipan Puthavathana said.

"Some months - such as May - all birds move away from Thailand. But no one knows exactly where they go. But after we follow their flight paths and study bird flu in the countries they pass we can identify where they become infected with the flu," she said

The team has been monitoring four open-billed storks and a lesser whistling duck since February.

"We chose the strongest birds in a group at Bang Len district in Nakhon Pathom. If the birds become infected and spread the disease they should die slower than others.

"The birds fly 30 to 40 kilometres a day. At the moment, the four storks are still in Thailand near where we found them.

Pilaipan said if the birds migrate and return to Thailand next year they will be caught and tested for the flu.  Microchips and the satellite-tracking costs are expensive and the team can afford to follow only eight subjects.

Pasara Puthamat

The Nation