NOVOSIBIRSK, May 19 (RIA Novosti) - Agricultural experts have detected bird flu antibodies in migratory birds in southern Siberia, Russia's agricultural watchdog said in a statement Monday.

The presence of antibodies means that either the birds have been in contact with infected birds or have survived avian influenza, but they are not a source of infection.

"Laboratory tests revealed antibodies of the H5 subtype of the virus in 18 blood samples taken from migratory birds in three regions in the Altai Territory and three samples taken at Lake Uvs Nuur in the Tuva Republic," Rosselkhoznadzor reported.

A total of 903 samples have so far been taken during the ongoing research. Over 4 million domestic birds in high-risk areas of a total of 5.8 million birds have been vaccinated and revaccinated as part of the anti-bird flu campaign.

No cases of bird flu have been registered in Siberia in 2007.