"I think bird flu fear has been over-emphasised," said Leslie Dierauf, director of the National Wildlife Health Center in Wisconsin, the United States.

"It's a very complex virus. In order to be highly pathogenic you have to mix and match with other viruses and mutate. There is no predictability to that. We don't know when it's going to mix, when it's going to match, or when it's going to mutate, or where," she said.

Rather than discouraging bird watching or calls for culling wild birds, it is more efficient to reduce contact between domestic fowls and wild birds and to improve biosecurity in the poultry industry.