It is more than a year since avian flu began to devastate wild birds in large numbers, and conservationists are fearful of what 2023 will hold. The highly infectious variant of H5N1 has caused Europe’s worst bird flu season and has spread across the globe with little sign of slowing.
In the UK, there were reports of some great skua dying from the H5N1 variant in the summer of 2021 but the mass die-offs started in the autumn and winter. More than a third of Svalbard barnacle geese in the Solway Firth, on the border of England and Scotland, – 16,500 out of 43,000 – died last winter.
A year later, there has been no letup, with Greenland barnacle geese on the Scottish island of Islay (the other main site where these geese overwinter) dropping dead in increasingly large numbers. “I’m sitting with a sense of dread that it definitely will get worse as I see more reports coming in from reserves across the UK,” says Claire Smith from RSPB Scotland. “I’m haunted by the numbers of dead great skua that I saw on Shetland in the summer and I’m avoiding going birdwatching on the coast.”
From April to mid-August 2022 avian flu ravaged colonies of seabirds in the UK, peaking in June at the height of the breeding season. These birds had previously been affected by H5N1 at very low levels. Seabirds generally migrate over summer, so numbers dropped again, but already there are outbreaks across the country among wintering waterbirds (which typically gather in large flocks, making them more vulnerable at this time of year). There have been cases in the south-west, the Midlands, East Anglia, Wales and the Isle of Man, each with numbers in the tens or low hundreds of dead water birds, with greylag geese, pink-footed geese, Canada geese and mute swans among the most affected.
Red-listed herring gulls across the north-east are already being impacted, with dead puffins washing up in Norfolk, which is unusual at this time of year when there is no stormy weather. They are yet to be tested, but the presumed cause of death is bird flu.
A northern gannet colony, with several dead birds, in Hermaness National Nature Reserve in Scotland, in July. Photograph: Henley Spiers/NPL
Cases in other groups of birds have been reported all over the country, and the RSPB called for a temporary ban on the release of game birds this year, to lessen the risk of spreading avian flu, but this was not taken up by government. Positive tests in peregrine falcons, buzzards, wild tawny owls and rooks have been recorded in recent months. Although there are not the same big die-offs, there are a lot of cases over a wide area, with more in urban and semi-urban areas. Positive tests are not an indication of the actual number of birds affected because few carcasses are found, let alone tested.
“We can expect HPAI [highly pathogenic avian influenza] to persist into the next breeding season and beyond, with unpredictable consequences,” a report from the International Seabird Group conference warned in November.
This will be the equivalent to our Covid pandemic, because we’re dealing with major outbreaks, major fatalities …Prof Kin-Chow Chang, University of Nottingham
It is a case of waiting to see what happens next, says Prof Ian Brown, head of virology at the government’s Animal and Plant Health Agency (APHA). Commercial hens can be shut up, but you cannot control the movement of wild birds.
“That horse has bolted,” he says. “It is unusual that this particular event is dominated by one particular strain over such a big geographical area. I can’t remember any time since 1996 [when H5N1 started], where a single strain has caused so much global spread.”
Bird flu is highly infectious, with scientists saying one bird can infect as many as 100, with the virus present in faeces, mucus, blood and saliva. “You need a very tiny quantity – a teaspoon of faeces will probably be enough to kill an entire house of chickens or turkeys,” says Brown.
The most common transmission between wild birds and poultry is probably indirectly, through birds in the nearby environment. Unpublished studies have shown that at 4C, the virus can stay in the environment for six weeks, according to Brown. It could be someone walking across a field and treading in infected bird droppings, and then failing to disinfect their boots before going into the poultry house. Or it could be transferred on bedding, or possibly via rodents.
Bird flu is highly infectious, with scientists saying one bird can infect as many as 100 others. Photograph: Maureen McLean/REX/Shutterstock
Brown says that more than 99% of cases in poultry in the UK have come from wild birds. Apha knows this by working out the genome of a virus and comparing what it looks like in wild birds with its appearance in poultry. The researchers also look at the affected farm and possible routes of infection into poultry houses.
Prof Kin-Chow Chang, from the veterinary school at the University of Nottingham, agrees commercial populations are getting it either directly or indirectly from wild birds. “The virus is very infectious, it doesn’t need a lot to start an infection,” he says
Little is known about the number of birds with antibodies. Because vaccinations for wild birds are not considered a feasible option, they will need to get some sort of herd immunity. Brown says: “There is a very small proportion of birds that can get infected, can recover from infection and then have immunity which means they won’t get that virus again. And over time that would build, but we don’t understand that at all. We need to do further work. That research is being commissioned and happening across the world.”
The present variant of H5N1 originated in south-east Asia, where it was found in commercial geese. For the past four years, these strains of avian flu have been highly pathogenic, meaning they cause severe disease and death. Scientists at the University of Edinburgh are trying to work out why the current strain is causing longer and larger outbreaks than those that came before, which will also help understand how the disease will evolve and spread in the future.
It could be down to changes in the surface proteins on the virus, meaning they can more easily attach to wild birds, or it may be more stable in the environment, so the virus could live in a pond over summer rather than breaking down in warm temperatures and sunlight as have previous bird flu viruses. It may become less damaging when sufficient numbers of birds have been infected, or the virus could evolve again, making it easier to spill into other species – including mammals and humans.
This variant of H5N1 has caused Europe’s worst bird flu season. Photograph: Steve Parsons/PA
In August 2022, Defra said that mitigation strategies “are not very effective in reducing transmission within seabird colonies”. However, there are other ways to reduce the pressures seabirds are under, as they have already been hit by a range of threats including habitat loss, overfishing and the climate crisis. Since 1986, the UK’s population of breeding seabirds has fallen by almost a quarter. Reducing these other pressures would make them more resilient to bird flu, says Smith.
The RSPB says it is generally not picking up dead birds on its reserves because it risks the health of the people doing it, and causes disturbance among living birds which could spread the disease further. Visitors are asked to keep dogs on leads and to clean their shoes thoroughly before and after visiting. However, other wildlife groups, such as those working for the National Trust, have decided to collect carcasses because it could result in the disease spreading further if they are scavenged by others. Conservationists are calling for better monitoring and surveillance of the disease in wild birds, as well as clearer arrangements for carcass collection.
Chang says: “This will be the equivalent to our Covid pandemic, because we’re dealing with major outbreaks, major fatalities, and possibly major disruption to the domestic poultry production market as well.”
The public should not touch dead or dying birds, and should report suspected bird flu cases to Defra on 03459 33 55 77.
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