Migration patterns: If a swan carrying avian flu should fly to Ireland, then Antrim or Down would be one of its most likely destinations, bird expert Dr Richard Collins said yesterday.
The zoologist and environmental consultant has been tracing the movement of swans for more than 20 years but said that the Scottish case of avian flu was proving to be totally unpredictable.
He said it was surprising that a mute swan had contracted avian flu as these were sedentary birds and they did not migrate. However, they often undertook random excursions. One known route was from Lancashire to the Isle of Man to Northern Ireland. Another was from the Hebrides to Northern Ireland.
"These are the shorter crossings. These birds are reluctant to head out over the open sea but if they see land then they are more inclined to go," Dr Collins said. "The distance is not so great."
Swans can fly at a speed of up to 50 miles an hour so it would take that long to get to Antrim or Down.
Dr Collins said the dead swan in Scotland either flew from an infected region or picked up the disease from another bird.
If the swan had flown from eastern Europe or Germany, then that was very surprising, given the distance involved. "The chances of this happening are terribly slim but then infected swans are known to exist in the Baltic and an infected swan has turned up in Fife. Is it a coincidence?"
It was more likely that a smaller migratory bird passed the virus to the swan, when they were feeding together, Dr Collins said.
The death of a duck could go unnoticed but a dead swan would be much more visible because of its size, he said.
Ducks such as teal and pochard have already began leaving Ireland to return to breeding grounds in the Baltic so it was unlikely that they would bring the disease here, he said.
The whooper and Bewick's swans were migratory birds but most of them were on their way to Iceland and Siberia now.
Summer migrants such as swallows and songbirds did not pose a great threat in the spread of avian flu as they "fed on the wing".
By eating in the air, they did not rummage in dirt and mix with poultry - two ways of spreading the disease.
"But there are a lot of unknowns here. The more I see, the less likely I am to pontificate on what might happen," Dr Collins said.
