This week sees the publication of a new RSPB Research Report that provides updated colony counts for seabirds across the UK, following the 2021–22 Highly Pathogenic Avian Influenza (HPAI) outbreak. In today’s blog, Linda Wilson, Senior Conservation Scientist, explains the key findings and what this tells us about the effects of HPAI so far on the UK’s seabirds.

Back in May 2023, a major programme of seabird surveys was launched across the UK designed to help us understand the impacts of Highly Pathogenic Avian Influenza (HPAI). The current H5N1 strain of this disease had become widespread in UK wild bird populations during 2022, particularly in seabirds and waterfowl, after being initially recorded in Great Skuas in the summer of 2021. The thousands of reported mortalities in 2022 demonstrated that HPAI had become one of the biggest immediate conservation threats faced by multiple seabird species. The seabird surveys undertaken in 2023 represent the first formal monitoring specifically undertaken to help assess whether these mass mortalities had translated into population-level impacts.

Headline results

Fourteen species were prioritised for targeted surveys in 2023 including Gannet, Great Skua, Common Guillemot, terns, and gulls (Table 1). The newly published RSPB Research Report summarises the results of these surveys and compares them with a pre-HPAI baseline count (mainly taken from the recent Seabirds Count census undertaken 2015–2021). Unfortunately, the report makes difficult reading; of the 13 species where data have now been analysed, nine showed declines of over 10% across the sites surveyed (Table 1), with declines in Great Skua (-76%), Common Tern (-42%) and Sandwich Tern (-35%) being particularly severe. These declines are seriously alarming given that they either come on top of previous declines experienced by some species prior to the current HPAI outbreak, or have reversed trends of previously increasing or stable populations for those few species which were faring better (see here for more details about these longer-term background trends).

Table 1. The % of the UK population surveyed for the 14 target species in 2023, and the % population change observed between the pre-HPAI baseline and 2023 counts. For context, an illustration of the UK background population trend observed prior to the HPAI outbreak is provided (increasing by >10%, decreasing by >10% or stable within -10 and +10%, taken from the Seabirds Count census).


Effects of HPAI

For Gannet, Great Skua and Roseate Tern (all of which previously had increasing populations) the declines of 25%, 76%, and 21% respectively can be largely attributed to HPAI and indicate the potential scale of the impact of this virus. Similarly, for Sandwich and Common Terns (previously relatively stable), HPAI is the likely cause of the 35% and 42% declines recorded respectively. Mass mortalities were recorded for all these species in 2022 and this has clearly had an immediate and devastating impact on the numbers of birds attempting to breed in 2023. For the remaining nine species that were already in long term decline, further work is needed to better understand the extent to which these more recent declines might be attributable to HPAI.

Although it is promising that there is evidence that some seabirds have showed signs of developing immunity, so far this has only been demonstrated in a few species. It remains unknown what proportion of species and individuals might become immune, how long immunity might last, how specific it is to a particular genotype, or what the longer-term impacts might be on survival and productivity.



Figure 1. This example map of the % change in Great Skua numbers at colonies across Shetland shows the severity and extent of declines that have occurred following the outbreak of HPAI. Special Protection Areas (SPAs) designated for Great Skua are named and shown as hatched boxes. For the full map, see the report.


Ongoing monitoring is essential

The report provides a valuable snapshot of the immediate population changes that have occurred since just prior to the 2021–22 HPAI outbreak for specific species and sites. However, the outbreak continues to affect seabird populations and significant further mortalities were recorded in 2023 for species such as Kittiwake, Black-headed Gull and Common Guillemot after data collection for this report was completed. It is imperative that further counts are undertaken in the coming years, both to fill remaining coverage gaps, but also to provide a time-series of data to help us understand the longer-term impacts of this disease. In 2023, our focus was on obtaining data on breeding abundance as this parameter was considered the most useful to assess the immediate impacts of the large-scale mortalities witnessed in 2022. However, there is an urgent need to also scale-up monitoring of other demographic parameters such as productivity and survival to obtain a more holistic understanding of how seabird populations respond to HPAI and to help guide where conservation actions for aiding resilience-building and population recovery are best focussed.

To find out how you could contribute to seabird monitoring, please visit the Seabird Monitoring Programme website.



While the project was led and coordinated by RSPB, it was a collaborative effort involving the British Trust for Ornithology, the Statutory Nature Conservation Bodies, and many other conservation organisations and individuals. Funding for this work was provided by the ScotWind developers of the East and North East plan areas; The Crown Estate (through the Offshore Wind Evidence and Change Programme); Scottish Government (via the ScotMER programme); Natural England; Natural Resources Wales; Department of Agriculture Environment and Rural Affairs. This project was also supported by the RSPB Avian Flu Appeal.


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