By Sophie Coxon, Kingfisher Writer

Published February 13th, 2023

Avian flu has swept through Europe this year, devastating seabird colonies and causing the death toll of wild bird populations to sky-rocket. With the onset of winter, concerns are rising over the impacts of migratory birds spreading the virus further afield.

The Avian Influenza Virus, also known as bird flu, is a virus which mainly affects avian species and usually causes only mild disease symptoms in wild bird populations. However, a large outbreak of a much more virulent strain (HN15) in 2021 has failed to simmer down, carrying into 2022 and causing severely high death tolls—the worst bird flu epidemic on record.

The symptoms of HN15 avian influenza present rapidly in wild birds after infection, and can include swelling of the head, respiratory difficulty, lack of coordination and paralysis. Besides impacting wildlife, the virus has had major impacts on farmed birds and caused lock-down conditions for domestic animals across many countries, including the UK. The reasons behind the unusual severity of the disease in the past two years are currently unclear, although its impacts have been hard felt, particularly in Scotland.

Scotland is well known for its rich diversity of seabird species, often crowding out the cliffs from view due to their density. The country has a large area of coastline with many small rocky islands and rock formations perfect for nesting sites, making it a vital seabird nursery for many migratory species.

Throughout the summer, seabird populations saw a significant decline due virus-induced death. In early May last year, abnormally high numbers of gannets were observed washed up on the east coast, and it was later confirmed that bird flu had spread to Bass rock, the gannets’ main breeding stronghold.

Further assessment by drone imagery conducted by the University of Edinburgh revealed the level of devastation caused by the virus. The colony was estimated to be less than half as populous as it had been the previous summer.

‘Seabird populations have seen significant decline due to virus-induced death.’

Many other species have also been infected by the HN15 strain; 28 species have been recorded across over 140 distinct locations in Scotland. These include seabirds, eider ducks, birds of prey such as buzzards, and two species of goose—barnacle and greylag. The heavily affected species share one trait in common: they form large breeding and nesting colonies of thousands of individuals, creating a host-reservoir for the virus and exacerbating its spread.

Though many species have been affected, Northern gannets and great skuas seemed to have suffered the most, but the underlying biology behind this is yet to be confirmed. The Bass Rock colony is the largest on the planet, and Scotland holds over half of the earth’s northern gannet population, so this is an urgent concern for the resilience of the species. Arctic terns, sandwich terns, cormorants, shags, fulmars, kittiwakes and puffins have also suffered, and guillemots are increasingly succumbing to the virus.

Many of these species have long lifespans and low reproductive output, and are not sexually mature until the ages of three or four. This means that population recovery will be a slow process, and a ripple effect may be felt throughout each species’ interrelated food web.

The spread to geese populations is also of particular concern, as these species undertake long-distance migrations to other continents. Barnacle geese migrate seasonally, spending summer in Greenland and Svalbard, and arriving in Scotland and the rest of the UK in early winter. Greylag geese follow a similar pattern, with many emigrating from Iceland to send winter in the milder UK climate.

This risks uninfected geese arriving in the UK and picking up the virus over the winter, with the potential to spread it to their summer destinations once the seasons change. In contrast, geese arriving from other areas could bring the virus into uninfected areas of the UK and spread it to wild bird populations in regions currently unaffected, worsening the problem.

NatureScot staff and volunteers are undertaking monitoring of geese populations for signs of HN15 infection. Through collaborating with colleagues in Iceland, they are helping to ensure that appropriate alerts and management strategies can be implemented if needed. This exchange of information is vital to understanding the disease dynamics within the geese populations, and how their migration patterns may influence the HN15 spread among local and global populations.

The organisation is also developing the new Scottish Avian Influenza Response Plan, which will set out management and mitigation strategies, and define the best monitoring and surveillance protocols for both optimal disease detection, and bird population recovery.

Activities which may affect wintering birds which may be infected have been cautioned, such as ringing, wildfowling, and public access to known breeding or resting grounds. Licensed shooting of geese causing agricultural damage may also be reviewed, however this is on a location-specific basis.

‘NatureScot staff and volunteers are undertaking monitoring of geese populations for signs of HN15 infection.’

An Avian Influenza Prevention Zone (AIPZ) was also employed over much of the UK, stating that domesticated birds must be strictly kept separate from wild populations to prevent crossover of the virus between species. This resulted in the country’s poultry being moved into sealed barns and other indoor spaces, temporarily affecting the ‘free range’ labelling of related food products. However, it was a necessary precaution as farms with confirmed cases of HN15 are required to cull their entire flock.

The HN15 virus poses little threat to humans, though has been reported to have spread into harbour seal populations and may therefore affect other mammal species in the near future. For now, the general public are advised to stay away from suspected bird flu cases and report any diseased or dead birds to DEFRA (Department for Environment, Food and Rural Affairs).

Other methods of control include limiting access to areas of reported cases, halting activities involving direct handling of birds, and encouraging strict hygiene of footwear around both domestic and wild bird areas.

Whilst the spread of the virus in wild populations is largely beyond human control, keeping bird feeders clean, and supporting the species in other ways such as providing food and water throughout winter may reduce stressors on bird populations as they face an uncertain future.

Featured Image: Raphael Rychetsky | Unsplash

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