03 July 2026
A study published in Biological Conservation provides the first long-term capture-mark-recapture analysis quantifying the demographic impact of Highly Pathogenic Avian Influenza (HPAI) on a colonial seabird species, the Northern gannet (Morus bassanus).
The findings show that a single multi-year H5N1 outbreak has profoundly altered population dynamics, with recovery projected to take nearly two decades.
Northern gannets are long-lived seabirds characterized by high adult survival and low reproductive rates, making population growth highly sensitive to increases in adult mortality. Researchers analyzed 15 years of demographic data from two major UK breeding colonies: Bass Rock (Scotland) and Grassholm (Wales).
The emergence of H5N1 in 2022 caused a dramatic increase in adult mortality:
- Bass Rock: Annual adult mortality increased from a historical average of 6% to 33%.
- Grassholm: Annual adult mortality increased from 11% to 47%.
This four- to fivefold increase in mortality resulted in estimated colony declines of 26% at Bass Rock and 38% at Grassholm by 2023.
Population projections indicate a prolonged recovery period. Grassholm is not expected to return to its theoretical pre-HPAI population size until 2041, approximately 19 years after the outbreak. Bass Rock is projected to follow a similar trajectory, with recovery residuals approaching zero only by 2040.
The authors emphasize that these projections assume no further HPAI outbreaks or additional environmental pressures, indicating that the estimated two-decade recovery period represents an optimistic scenario.
Lane et al. (2026). HPAI drives a fourfold increase in adult gannet mortality which requires two decades recovery time. Biological Conservation 319, 111887.
