The emergency response comes after 556 dead birds were removed from Stonehaven Beach and Cruden Bay in Aberdeenshire this week.

Carcass collection operations are expected to take place at Balmedie Beach on Wednesday and testing is now taking place to determine the exact cause of death.

A NatureScot spokesperson said: "There are many potential causes of mortality in wild birds, however it is looking increasingly likely that recent deaths along the east coast of Scotland may be due to the current avian flu outbreak.

"Within the past few days we've been receiving reports of mass mortalities of seabirds from Caithness down to Berwickshire.

"Testing will be carried out by the Animal and Plant Health Agency, to determine whether these deaths are a result of avian flu or some other cause."

Scotland's nature agency said Highly Pathogenic Avian Influenza (HPAI) had been confirmed in sandwich tern, common tern, kittiwake, herring gull, black-headed gull and guillemot birds so far this year.

At Forvie National Nature Reserve, more than 200 sandwich terns have died from bird flu. Signs of the virus have also been spotted in common and arctic terns, with further test results awaited.

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Kittiwakes have also tested positive for avian flu on the Isle of May National Nature Reserve in the Firth of Forth.

NatureScot said the overall picture was "not yet clear" with tests on some birds in other parts of the country having come back negative.

Wildlife manager Alastair MacGugan said: "While we are thankfully not seeing the large numbers of dead birds around breeding sites that we did last year, this development is really concerning and we're working hard with all partners in Scotland's avian flu task force to understand what is happening and take action to make our wild bird populations more resilient.

"Testing is key to unravelling just what is happening to our seabirds.

"We are working with Scottish government and the Animal and Plant Health Agency to coordinate testing and when possible, to carry out post-mortems on dead birds.

"This gives us a clearer picture on whether starvation or avian flu is the main cause of the current deaths we are seeing."

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Paul Walton, head of species Scotland at the RSPB, said seabird numbers had declined by nearly 49% between 1986 and 2019 prior to the "devastating impacts" of bird flu last year.

He said it was time for conservation efforts to be "prioritised and resourced" to help these "incredible creatures thrive into the future".

Members of the public who spot a dead or sick bird are being warned not to touch it.

Sightings can be reported via the government website or by phoning the helpline on 03459 33 55 77.