New research has identified which groups experienced the biggest losses from bird flu outbreaks between 2000 and 2020.
5 min read
Outbreaks of Highly Pathogenic Avian Influenza (HPAI) can cause large population losses across a wide range of bird species. By combining data from 40 different mass mortality events across the world, new research shows that some bird groups, such as gulls, terns and other seabirds, appear more likely to suffer significant population losses, than others, such as waterfowl.
HPAI is a contagious, and potentially deadly, viral infection which spreads between birds through saliva, nasal secretions, droppings, predation and scavenging. Where outbreaks occur, thousands of birds can die, causing an initial drop in population size.
Researchers at the RSPB collated datasets from across the world where bird populations were monitored before, during and after HPAI outbreaks which occurred pre-2020.
They found that most populations experienced a decline immediately following outbreaks, with an average 17% drop in number of birds. In most cases, populations recovered following this initial impact and bounced back within a few years. However, in 25% of cases, populations did not recover from these initial declines within the post-outbreak monitoring period (which varied between 4-17 years).
Gulls, terns, penguins and ducks, experienced some of the strongest initial declines after disease outbreaks. Populations of African Penguin, Cape Cormorant, Common Pochard, Great Black-backed Gull, Peregrine Falcon, and Tufted Duck failed to recover following HPAI outbreaks.
Seabirds often nest in dense colonies, living closely alongside each other, making it easy for infections to spread quickly between individuals. Their long-distance feeding routes mean it is also possible for infections to spread between distant colonies. The long-lived nature of many seabirds also means the initial impacts of mass mortality events may not become apparent until there is a shortfall in breeding age adults.
However, there was also evidence of resilience in some affected populations. Waterfowl species (ducks, geese and swans) appeared to suffer less short-term population impacts. These species tend to raise large numbers of young and therefore may be able to bounce back quicker following a mortality incident. There is also evidence of natural immunity spreading rapidly amongst some affected waterfowl populations. However post-2020 we have seen an increase in the size and severity of outbreaks in these species.
Since 2020, we have seen an escalation in the impacts from the virus globally with even more species and countries affected by HPAI, and the virus now even detected on Gough Island, one of the most remote inhabited islands in the world. There has also been an increase in the severity of outbreaks occurring during the breeding season. This means as monitoring continues, we may see different and potentially more severe population impacts from post-2020 outbreaks.
Since the current strain reached the UK in 2021, the greatest impacts in UK birds have been seen in seabirds, but we’re increasingly concerned about the ongoing impact on birds of prey. There is evidence of reduced breeding success in both White-tailed Eagles and Golden Eagles, with local population declines observed in Peregrine and Buzzard. The consistently high numbers of HPAI cases being seen in Mute Swans over a number of years is also worrying.
Continued population monitoring is essential for making sure we are able to identify species most vulnerable to the impacts of HPAI. Action to reduce additional stressors on vulnerable wild bird populations and identifying ways we can support the recovery of threatened populations will be key to protecting our most vulnerable species through future HPAI outbreaks.
This work was funded by our RSPB Avian Flu Appeal, which directly supports research and action addressing the threat of HPAI to our wild birds. Thank you so much to everyone who supported this appeal. You can now help our scientists undertake vital research so we can save our wildlife by donating to our Wildlife Disease Fund.
Support our bird disease research here.
