The Russian officials has blamed H5 bird flu for deaths of around 4,000 wild ducks in southern Krasnodar region.
"This is the H5 virus, the strain is being confirmed," a spokeswoman for the Krasnodar region branch of Russian agriculture watchdog Rosselkhoznadzor told AFP.
The birds' remains were now being tested, she added.
The dead birds have been found on lakes near the Black Sea resort town of Anapa.
The region has gone on high alert, with poultry and humans now being vaccinated.
"All of these are protective measures, it's better to be on the safe side," the spokeswoman added.