Scottish Seabird Centre

22 May 2025

By Emily Burton, Senior Conservation Officer

Perched dramatically off Scotland’s East Lothian coast, Bass Rock is among the world’s most iconic seabird islands. During the Spring and Summer, it’s home to one of the largest colonies of Northern gannet in the world.

Gannets are bright white, with distinctive black wingtips and a dusky yellow head. They are the UK’s largest seabird, with a wingspan of up to 2 metres. Every year, they return to this volcanic rock in their thousands to breed, each pair raising a single chick.

The Scottish Seabird Centre’s conservation team manage the island for seabirds, on behalf of the island owner. The team also play a part in monitoring the population of gannets, tracking how many of them are breeding on the Rock each year. This challenging task is completed as part of a broader partnership of scientists, which includes The University of Edinburgh’s School of Geosciences, UK Centre for Ecology & Hydrology, and Edinburgh Napier University.

A high-resolution drone survey, carried out in July 2024, provided a detailed new look at the Bass Rock gannet colony. The results give us a clearer understanding of how the birds are faring in the wake of recent challenges—especially the devastating outbreak of highly pathogenic avian influenza (avian flu) during 2022.

What Did the Drone Survey Find?

Using a drone-mounted camera, detailed vertical images were captured that covered about 97% of the entire colony. From this, three independent counts were carried out, giving an average of 44,447 Apparently Occupied Sites (AOS). An ‘apparently occupied site’ in the colony is an area occupied by a single gannet, a pair of gannets, or unaccompanied chick. After adjusting for the small portion of the colony that wasn’t visible in the image, the team estimated the total number of AOS across the Bass Rock in 2024 to be around 46,045 AOS.

But here’s the tough part: that number indicates a 6.7% decrease compared with the last survey completed in 2023, in the areas that were fully counted both years. In addition to this, comparison of the estimated total population between 2023 and 2024 indicates a decrease of around 11%. Although these figures are estimates (so should be treated with caution) these results suggest that the gannet population has not yet started to recover from the impact of the avian flu outbreak in 2022.

Despite the overall population drop, there is some good news. The 2024 survey didn’t turn up many signs of ongoing illness. Very few dead birds or unattended chicks were spotted, which (along with accounts from those working on the island in-person throughout the season) suggests that the avian flu did not return during 2024. Also, the presence of so many chicks implies that foraging conditions were good, allowing parents to feed their young successfully.

Another highlight of this year’s survey was the quality of the data itself. Thanks to the high-resolution drone imagery, researchers were able to count with greater accuracy and consistency than in previous years, when they relied on images taken with hand-held cameras from manned aircraft. In fact, a detailed study of the different counters showed that there was no significant difference in how they interpreted the images. This could mean that future surveys might not need to be repeated as many times, which would save both time and money—great news for conservation efforts.

Why It Matters

The Northern gannet is an impressive and beautiful bird. Their presence on the Bass Rock has long been celebrated in Scotland, and the colony provides an incredible opportunity for people to see an immense seabird city first-hand. Keeping tabs on the colony allows us to better understand how gannets are faring, both in Scotland and around the world. In addition, these results also help us to understand broader issues, like disease, climate change, and food availability.

So, while the news in 2024 isn’t exactly what we were hoping for, the absence of new flu cases during 2024 and improved survey methods are promising signs. With continued monitoring and care, there’s still hope that this spectacular seabird colony can bounce back in the years ahead.

Learn more about the Bass Rock counts and read the full report here .