6 February 2015 Last updated at 04:02
By Helen BriggsEnvironment Correspondent
Migratory birds may be spreading viruses that cause bird flu around the world, say scientists.
Outbreaks in poultry may become more common in the future, especially in ill-prepared countries, they warn.
A severe strain found at a duck farm in the UK last year may have been carried by wild birds out of Russia, according to Dutch researchers.
The virus is a low human health risk, but wild birds on long migratory routes should be monitored, they say.
H5N8 is a strain of bird flu that appeared late last year in Russia, East Asia, North America and four European countries, including the UK.
The infections led to millions of poultry being culled.
In the UK, ducks were affected at a farm in Driffield, Yorkshire. Another outbreak of bird flu in Hampshire this week is of the H7N7 form of the virus, which is less severe.