Workers wearing masks and protective clothes gassed thousands of ducks in southwest France on Friday, in a massive cull that was ordered in an attempt to prevent a spread of the H5N8 bird flu virus. At one farm in the village of Latrille, in the heartland of duck and geese rearing country, 8,000 ducks were taken by hand and put in coloured metal containers where carbon dioxide was piped in to kill them, normally within seconds.