From the BBC
There are now restrictions in place
The Scottish Executive has extended surveillance zones in Scotland to include 175 properties with 3.1 million birds, as well as free-range poultry.
The dead mute swan was found in Cellardyke, Fife, eight days ago. Other birds are being tested.
The H5N1 virus does not currently pose a large-scale threat to humans as it cannot pass easily between people.
But experts fear the virus could mutate to gain this ability, and in its new form trigger a flu pandemic, potentially putting millions of human lives at risk.
Scotland's Chief Veterinary Officer Charles Milne, announcing confirmation of H5N1, said a surveillance zone was being extended to 965 sq miles (2,500 sq km).
The zone contained 175 registered premises, with in total 3.1 million poultry.
About 48 were free-range premises with 260,000 birds.
A total of 14 cases of birds are being checked for bird flu from Scotland including 12 swans and two other species.
Mr Milne said: "There is no indication that any of these are positive."
Farmers are being ordered to house their birds where possible, or separate them from wild birds.
However, the Scottish Executive said it would be "disproportionate" to house poultry UK-wide.
Officials were also banning the gathering of birds and enhancing their surveillance.
An initial 1.8 mile (3km) protection zone was set up around Cellardyke on Wednesday, surrounded by a six-mile (10km) surveillance zone.
The infected bird, a native UK breed, was collected from Cellardyke harbour on 30 March - a day after it was reported by a resident.