Counting Northern Gannets on Bass Rock

Many amazing seabird species have shown major population declines in recent years. In contrast, the Northern gannet has been increasing in breeding numbers for over a century (Jeglinski et al. 2022). Nowhere has this increase been demonstrated better than the population on the Bass Rock. Here, numbers increased from around 3000 pairs in 1904 to over 75,000 Apparently Occupied Sites (AOS) in 2014, when it became the world’s largest colony of Northern gannets (Nelson 2002, Murray et al. 2014). An Apparently Occupied Site in the colony is an area occupied by a single bird or pair of birds, irrespective of whether nest material is present.

However, things changed abruptly in 2022 when Highly Pathogenic Avian Influenza (Avian Flu) resulted in unprecedented mortality in gannet populations throughout the North Atlantic (Lane et al. 2023). The disease was confirmed on the Bass Rock on 4 June 2022 and 5035 dead birds were identified in images taken by a drone on 30 June 2022 (Glen Tyler in Lane et al. 2023). The drone images and observations made in the colony throughout the 2022 season indicated that the number of gannets present in the colony had dramatically reduced and was consistent with a significant population decline.

Carrying out a count of the colony in 2023 was a high priority to assess the impact of the Avian Flu outbreak. Advances in the technology now available to monitor breeding gannets and interpret survey results also brought with it opportunities to undertake drone surveys and machine learning trials.

To complete this essential research, The Scottish Seabird Centre worked in close collaboration with The University of Edinburgh School of Geosciences, The University of Edinburgh Airborne Research and Innovation Facility, UK Centre for Ecology & Hydrology, and Edinburgh Napier Centre for Conservation and Restoration Science. We are very grateful to all the individuals and organisations involved for bringing their extensive expertise and commitment to this project.

© School of Geosciences & Airborne Research and Innovation Facility, University of Edinburgh

Summary of Count Results: 2023

A drone survey of Northern Gannets on the Bass Rock was carried out on 27 June 2023. The survey covered approximately 85% of the colony and three independent counts of the drone imagery were made. The total Bass Rock population was estimated to be 51,844 AOS. Comparison of the 2023 count with the same count areas in 2014 indicated a decrease of 31%.

To find out more about how this assessment was completed and the methods and assumptions that underpin these results, please read the 2023 Bass Rock Count Report:

2023 Bass Rock Count Report

© Susan Davies

Find out more

Discover more about how the development of a deep learning neural network fed into our research on Bass Rock during 2023 in this research paper:

Quantifying the Impact of Avian Influenza on the Northern Gannet Colony of Bass Rock Using Ultra-High-Resolution Drone Imagery and Deep Learning

Tyndall AA, Nichol CJ, Wade T, Pirrie S, Harris MP, Wanless S, Burton E. Drones. 2024; 8(2):40.