In the Shetland islands alone, the virus has caused the deaths of thousands of gannets and hundreds of great skuas, known as bonxies, with cases also confirmed in great black-backed gulls and eider ducks in the past few weeks.
Globally important seabird colonies in places as far-flung as St Kilda and Foula have also been impacted.
Countless fatalities have been recorded elsewhere too, with a wide range of species affected, including birds of prey, wildfowl, waders and even garden favourites.
A white-tailed eagle, peregrine falcons, buzzards and red kites have died, as well as several duck, geese and swan species and at least one critically endangered curlew.
Nearly 40 per cent of the global population of Svalbard barnacle geese, which spend winter around the Solway Firth, are thought to have perished over the course of the outbreak – with estimates suggesting around 16,000 of the birds have been lost.
But Shetland and the north-east of Scotland seem to have been the hardest hit by avian flu, according to Scotland’s nature agency.
“In north-east Scotland wildfowl was mainly affected, although several other bird groups may have also been hit by the virus,” said Glen Tyler, NatureScot’s marine ornithology policy and advice officer in Shetland.
“Shetland’s seabirds were infected in late spring and early summer, and there has been a significant die-off of gannet at Troup Head, as well as great skua and gannet at St Kilda.
“We have reports of smaller numbers of birds from many other areas, from the Western Isles and Orkney especially.”
Experts are unsure why the bird flu, which broke out last year, but abated after a few months, has been showing such a resurgence.
But it is thought the resurgence could be down to the spring breeding season getting underway, when birds congregate en-masse and create what has been described as “super-spreader” conditions.
Mr Tyler added: “It is not clear why birds in Shetland and north-east Scotland were more affected, if it has been, other than the virus was already shown to be active in Shetland last summer and it is spreading in seabird colonies.
“Shetland has some of Scotland’s largest colonies and St Kilda is a huge colony, so they are the biggest ‘resource’ for the virus.
“Other major colonies such as the Forth islands appear to have escaped so far.
“Great skua and gannet remain by far the most frequent casualties in Shetland.”
A special protection and surveillance zone has been set up on the island of Whalsay in Shetland after bird flu was confirmed at a poultry holding earlier this week.
People are advised not to touch or pick up dead or visibly sick birds they may find.
Anyone discovering a single dead wild waterfowl or bird of prey or five or more wild birds of any other species in the same place should report them to the Defra helpline on 03459 335577.
Avian influenza primarily affects birds, posing a “very low” risk to humans.
The infection is passed between birds through direct contact or contaminated body fluids and faeces.
It can also spread via feed and water or dirty vehicles, clothing and footwear.