Avian Influenza

BTO is dedicated to tackling the challenge of avian influenza. Here you'll find more information on the virus and disease it causes, its impact on our wild bird populations and the work being done by BTO to mitigate its impacts.

What is avian influenza?

Avian influenza, which is sometimes referred to as avian flu or bird flu, is a variety of influenza caused by viruses adapted to birds. Avian influenza is similar to human flu, in that it is an illness caused by strains of influenza viruses adapted to a specific host.

Avian influenza strains are categorised into two types based on their potential to cause disease (their pathogenicity): these are high pathogenicity (HPAI) and low pathogenicity (LPAI).

  • The most well-known HPAI strain is H5N1, and this is the strain that has been behind the 2021/2022 outbreaks in UK poultry and wild birds.
  • Avian influenza is a different disease to avian pox.

Health and safety

The risk of avian influenza transmission to humans is very low, but you should not handle sick or dead birds if you come across them.

Reporting avian flu

Avian influenza is a "notifiable disease". For the latest information, please see our guidance on reporting avian influenza.

Key symptoms of HPAI in birds

  • The main clinical signs of HPAI in birds are a swollen head; blue discolouration of the neck and throat; loss of appetite; respiratory distress such as gaping beak, coughing, sneezing, gurgling, rattling; diarrhoea; fewer eggs laid; increased mortality; neurological signs such as trembling, falling over, swimming or walking in circles.
  • Clinical signs can vary between species of bird and some species, e.g. ducks and geese, may show minimal clinical signs.

About the 2021/ 2022 HPAI outbreak

Background and origins

Over the winter of 2021 and 2022 an outbreak of HPAI was confirmed in Barnacle Geese wintering on the Solway Firth.

Barnacle Geese. Sebastian.

These birds were from the Svalbard breeding population and it has been estimated that many thousands of individuals died as a result.

  • Previous outbreaks of HPAI have tended to hit wintering waterfowl, subsiding as wintering flocks disperse.
  • Unusually, on this occasion, the HPAI virus (subtype H5N1) spread into our globally important colonies of nesting seabirds. Monitoring work carried out by the Animal and Plant Health Agency (APHA) has also confirmed HPAI in other (non-seabird) species including raptors, wildfowl, waders, gamebirds and others.

Impact on breeding seabirds

From late spring 2022, increasing numbers of reports of the disease were received from seabird colonies around the northern UK.

Gannet colony. Edmund Fellowes / BTO

Very large numbers of breeding seabirds, including significant numbers of Great Skuas and Gannets, are thought to have died as a result. Further south, breeding tern colonies were also impacted by the outbreak.

  • More than 2,200 Great Skua deaths (equivalent to 11% of the British and 7% of the world population) have already been reported by NatureScot, including 1,000+ from the largest colony of Foula (Falchieri et al. 2022).
  • Gannet mortalities also appear widespread, from Alderney in the Channel Islands in the south to Noss, Shetland, in the north.

Why are we so concerned about the impact on seabirds?

Seabirds are already vulnerable to other threats

Many of Britain's seabirds are already Red or Amber-listed in the UK, because their populations are being negatively impacted by other threats. They are particularly vulnerable to the effects of climate change, for example. 

Britain and Ireland support a large proportion of global seabird populations

Together, Britain and Ireland support 25% of Europe's breeding seabirds, including more than 50% of the world population of species which have been severely impacted by HPAI, such as Great Skua and Gannet. Population losses in the UK therefore have a significant impact on these species' global status.

Seabirds are slow to recover when their population declines

Seabirds tend to be long-lived and slow to reach sexual maturity.

  • This means that seabird populations take a long time to recover from losses, because a smaller proportion of the remaining population is able to breed. 

Several seabird species are also only able to lay one or two eggs.

  • For example, birds in the group Procellariformes (tubenoses) - like shearwaters and petrels - are what is known by ecologists as 'k-selected'; that is, they have evolved to give a lot of care to a single chick (rather than less care to many chicks, which is known as 'r-selected').
  • They lay a single, large egg, and make only one breeding attempt each year, even if they lose their egg. So even among the breeding portion of the population, only one chick can be raised per pair, slowing recovery down even further.

Seabird mortality from HPAI is high

The high level of mortality for seabird species suggests that they are very vulnerable to the disease. This could be because they have never been exposed to it before, or because the virus has rapidly adapted to infect seabirds. 

    Looking ahead: migration and the impact of AI on wintering waterfowl

    Given the usual vulnerability of waterbirds to the disease, the autumn and winter is a period of particular concern because Britain and Ireland host important wintering waterfowl populations and are part of a wider flyway that links populations from many different breeding areas.

    The potential for migratory birds to spread the disease across continents is highlighted by recent evidence from North America (Caliendo et al. 2022).

    Help us protect vulnerable winter birds

    With your support, we can help devastated bird populations recover.

    Donate to the Avian Influenza Appeal today

    What is BTO doing to help tackle HPAI?

    As the custodian and coordinator of national datasets of wild bird populations, including their abundance, distributions, and demographics, we are uniquely placed to provide insights and commentary on this issue.

    Collaborative science

    We are working with the Joint Nature Conservation Committee, Country Nature Conservation Bodies (CNCBs), DEFRA, APHA, Scottish Government, RSPB, and other NGOs and administrations to understand the impacts on bird populations and how to tackle the avian flu challenge.

    Our scientists have coordinated regular meetings with these other organisations, sharing our expertise and data, so that efforts to tackle the outbreak and address its longer-term impacts are informed by the available evidence.

    Utilising volunteer data

    Maintaining, supporting and growing our network of volunteers provides a vital service to the wider conservation community and provides crucial information for a wide array of uses, including the assessment of HPAI impacts.

    Thanks to the efforts of birdwatchers using BirdTrack, our volunteers and supporters, on the ground responses to the virus are informed by the best available evidence of wildbird numbers and movements.

    • This information is used to assess the current risk that avian influenza poses to different species groups, which is used to guide BTO ringing activities. 

    Assessing vulnerability of bird species

    BTO staff are carrying out vulnerability assessments, identifying those species and populations at greatest risk from the outbreak. This information will help to inform conservation responses and the prioritisation of resources.

    Our modelling work will help to reveal the likely medium-term impacts of the outbreak on populations, and the risk that future outbreaks may pose to their future conservation status and in some cases, extinction risk.

    • This is particularly relevant in the case of our breeding seabirds, which tend to be long-lived, slow to reach sexual maturity and, as a consequence, slow to recover from substantial losses.

    Looking ahead: BTO's HPAI programme of work

    HPAI will continue to be a major focus of BTO's work in 2022/23 and beyond. Given the scale and potential impact of this problem, we have outlined an extensive programme of work in response.

    As we move into winter our volunteer network is likely to act as one of the early warning signs of further significant outbreaks in wintering wildfowl and waterbirds.

    • This outbreak has identified a lack of a centralised repository for the reporting of large wild bird mortalities. We have asked Wetland Bird Survey (WeBS) counters, who undertake monthly surveys of many of our larger wetlands and estuaries, to record bird mortalities as they do so.
    • This will provide structured information on the potential spread of significant waterbird mortality through the winter to inform planning.
    • Changes in the numbers of dead ringed birds reported to the BTO provide a realy good source of data to identify additional levels of mortality associated with the disease, and we are currently analysing these to identify the most affected species and locations.

    Informing future planning and decision-making

    We have been developing tools to inform future planning and decision-making. Through a collaboration between EURING and EuroBirdPortal, funded by the European Food Safety Authority (EFSA), BTO has developed a migration mapping tool to inform the management of future Avian Influenza outbreaks.

    • This approach can be extended to develop predictive models of AI spread in domestic birds based on wild bird abundance and movements across Europe.

    Informing our supporters

    Our membership magazines, other supporter communications and social media feeds continue to carry articles and updates about HPAI and our response to it. These include a blog post published in mid July and articles in our membership magazine, one on the impact of the outbreak and one demonstrating the value of the monitoring tools we have in place.

    We have done a lot to respond to this crisis and our plans are to continue to play as big a role as we can in helping to safeguard bird populations and assist with their recovery.

    • We will provide supporters with regular updates about developments in this area and, in particular, about the progress we are making to help.

    Funding our work

    We are funding this work both from our core funds, from scheme budgets, and through targeted fundraising efforts. An approach to major donors was mailed in August 2022, and a wider fundraising appeal was mailed to our supporters in November 2022.

    Monitoring the impacts of a deadly outbreak

    With your support, we can help devastated bird populations recover.

    Donate to the Avian Influenza Appeal today

    Frequently asked questions

    What should I do if I find a dead bird?

    Birdwatchers can be of great assistance in staying alert for unusual cases of mortality or sickness in wild birds. Many thousands of birds die every week of natural causes and so it is not unusual to occasionally find dead individuals.

    If you notice unusual avian mortality in Great Britain, however, you should call the Defra helpline on 03459 33 55 77 (Mon-Fri 8am to 6pm) and select option 7. In Northern Ireland, wild bird mortality incidents should be reported to the DAERA Helpline: 0300 200 7840.

    You should call the Defra helpline if you find:

    • one or more dead bird of prey or owl
    • 3 or more dead gulls or wild waterfowl (swans, geese and ducks) 
    • 5 or more dead birds of any species

    Helpline staff will be able to advise you on whether a response is required e.g. whether the bodies be collected by a representative for testing; not all birds are tested, but collating sightings may reveal patterns of mortality.

    Where possible, avoid directly touching any dead birds. If you move a dead bird e.g. if a cat brings one into your house or you need to check if it is ringed, invert a plastic bag over your hand and pick the bird up in the plastic.

    If the bird is ringed, report the ring details to BTO using the EURING website, then draw the bag over your hand and tie it up and dispose of it in your usual household waste, and wash your hands with soap and water.

    Where can I get further information?

    • Official surveillance data are publicly available via the Government’s APHA Avian Influenza reports (updated weekly) and summarised in their regular HPAI Outbreak Assessments. These data provide useful (but necessarily limited) insights into the range of species affected, as well as the locations of outbreaks and some detail on numbers.
    • Read the general government guidance on avian influenza for England, guidance for Scotland, guidance for Wales and guidance for Northern Ireland. The guidance includes the actions required by poultry keepers to protect their birds from disease in prevention zones.
    • The EURING migration mapping tool uses recoveries of birds marked with individually identifiable rings to map migration routes in both space and time for wild birds moving to and from Britain and Ireland.
    • The latest on the situation across Europe is reported by the European Food Standards Agency, and on the global situation by the World Organisation for Animal Health.


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