Significant Decline in Bass Rock Gannet Colony
The population of the world's largest northern gannet colony, located on Bass Rock off North Berwick in the Firth of Forth, has decreased by nearly a third following an "unprecedented" outbreak of bird flu.
Researchers estimate that Bass Rock is home to over 100,000 seabirds; however, breeding success remains low despite the large population.
Drone surveys conducted in 2025 indicated that the colony numbers have "stabilised" since the highly pathogenic avian influenza (HPAI) virus severely impacted the breeding season in 2022.
Nonetheless, the overall population is believed to have declined by approximately 30% since the outbreak.
In July 2025, aerial photography identified an estimated 52,459 Apparently Occupied Sites (AOS) used for nesting. This figure represents an increase of about 6,000 AOS compared to 2024 but remains roughly 22,800 below the last comprehensive pre-HPAI count conducted in 2014.
A 'site' within the colony refers to an area occupied by a single bird or a pair of birds.
Research Collaboration and Findings
The research was undertaken by a collaborative team from the Scottish Seabird Centre, Edinburgh Napier University, the University of Edinburgh's School of Geosciences, and the UK Centre for Ecology and Hydrology.
The team reported declines across most count areas with "no evidence of a major population recovery".
"It has been devastating to see the impacts of avian flu on seabirds in recent years, including on the Bass Rock where the gannet population has plummeted by almost a third.
It's critical that every effort is made to reduce pressures on these incredible birds to help them recover.
It's an astonishing island and home to one of the world's great wildlife spectacles that we must conserve for future generations."
— Emily Burton, conservation manager at the Scottish Seabird Centre
Impact of the 2022 Outbreak and Other Affected Species
Nature Scot estimated that a minimum of 11,175 gannets died during the 2022 HPAI outbreak.
Other seabird species, including great skua, guillemot, and kittiwake, were also severely affected by the virus.
Globally, it is estimated that approximately 97 million birds died due to avian influenza.
Monitoring Breeding Success with Technology
The research team also monitored the breeding success of gannets by using remote ground-based cameras.
They found that the loss of experienced adult birds, combined with ongoing challenges seabirds face at sea, has negatively impacted breeding success.
"By combining drone surveys with remote camera technology, we've been able to gain an unprecedented level of insight into breeding success across the colony.
The drone imagery has allowed us to estimate population size with far greater clarity than previously possible, making the counting process much more accurate and efficient, while the cameras have provided a uniquely detailed view of breeding behaviour."
— Dr Sue Lewis, Edinburgh Napier University
"Following the devastating impacts of 2022, these technologies have been invaluable in helping us better understand how the colony is recovering."
