Investigations were under way yesterday following the discovery of 80 dead gulls in Orkney.

Investigations were under way yesterday following the discovery of 80 dead gulls in Orkney.

Tests for avian flu are currently being carried out, but experts stressed that the birds did not have typical symptoms of the disease. Indeed many had been covered in a blue substance.

All the birds found dead or dying are black-backed gulls and most have turned up at the Peerie Sea, a land-locked body of water in Kirkwall which drains into the sea. They were discovered at roughly the same spot where 20 birds were found dead just over a year ago.

The death toll in the latest incident reached 80 yesterday as animal welfare experts recovered more corpses, as well as gulls close to death and finding it hard to swim. They were carefully collected and then humanely destroyed.

More of the birds were seen on the shoreline of the nearby Hatston industrial estate.

Some of the dead gulls have been sent to the Scottish Agricultural College veterinary laboratory in Thurso, where experts will try to determine what killed so many of the large and normally powerful birds.

Willie Stewart, a veterinary officer with the Scottish Government's environment and rural affairs department, said that after the deaths of so many gulls, it was important to check for signs of bird flu.

"But the symptoms are not typical of avian flu," Mr Stewart said.

Scottish SPCA officer Mike Lynch said: "It's very unusual and of major concern to have so many birds, all black-backed gulls, die in this way."

Around one-fifth of the birds had their feathers contaminated with a blue substance like a dye. Some showed signs of blue colouring inside their beaks as well.

One theory under investigation is that the gulls may have eaten something poisonous elsewhere, before flying to the Peerie Sea to swim and rest.