New study examines how the HPAI epidemic affected local seabird colonies
Seabirds that survived recent bird flu outbreaks have continued to reproduce, although overall breeding performance remains notably low, according to a new study.
The paper, led by Edinburgh Napier University’s Dr Sue Lewis, in a collaboration with conservation scientists and staff from the RSPB, the Scottish Seabird Centre and the UK Centre for Ecology & Hydrology has been published by the international avian science journal Ibis.
They studied breeding success in Northern Gannets at the Bass Rock in Scotland and Bempton Cliffs in England during 2023.
Bird flu had a devastating effect on seabirds across Europe and North America between 2021-2023, with gannets, known for their spectacular plunge dives, among the hardest hit. Outbreaks of highly pathogenic avian influenza (HPAI) occurred at all but one gannet colony across their North Atlantic range in 2022, causing mass mortalities on an unprecedented scale.
For this study, scientists compared the breeding success of birds with black eyes – a striking side-effect of an HPAI infection – and those with normal, pale blue eyes.
Overall, they found that breeding success of birds with black eyes did not differ from birds with blue, suggesting that gannets who survived HPAI infection were able to raise chicks just as effectively as those that showed no sign of a past infection.
Breeding success across both groups in 2023, however, was still markedly lower than long-term records – with nest failure rates almost doubling.
At the Bass Rock – which was home to the world’s largest colony of the species before the epidemic – pairs fledged an average of just 0.56 chicks, compared to 0.78 in the 1960s. Meanwhile at Bempton Cliffs, success averaged 0.62 chicks per pair, down from a pre-epidemic mean of 0.81 between 2009 and 2021.
A black-eyed gannet with a chick. Picture credit: Amy King
The authors of the paper believe the dip could be down to birds having to form new partnerships after the death of their long-term partner and less experienced breeders making up a larger share of the population, in combination with a density of nests after mass mortality. The summer heatwave of 2023 may also have played a role.
The findings highlight the complex consequences of disease outbreaks in wild populations, showing that even when survivors appear healthy, impacts to the wider ecosystem can persist.
Lead researcher Dr Sue Lewis, from ENU’s Centre for Conservation and Restoration Science, said: “While it is reassuring that gannets that recovered from avian flu are able to breed, the overall reduction in breeding success is a serious concern.
“The results suggest that population recovery may be slower than hoped, even if survivors are still able to breed.
“Survivors are breeding as well as their peers, proving that gannets are remarkably resilient birds. But with bird flu still circulating and climate extremes adding new pressures, continued vigilance is needed to ensure that these majestic plunge diving birds remain part of our coastal environment for generations to come.”
Dr Jude Lane, from RSPB’s Centre for Conservation Science said: “HPAI has had a devastating impact on many of our seabird populations, which are already facing increasing threats from development and climate change.
“Long-term monitoring will be key to tracking their recovery and understanding whether HPAI infections have hidden effects on survival or behaviour.
“However, it is essential we also take steps to secure long-term resilience for seabirds, such as protecting feeding grounds and reducing bycatch.”
Gannets diving at the Bass Rock. Picture credit: James Glossop
Emily Burton, Senior Conservation Officer with the Scottish Seabird Centre Conservation Team, said: “Black-eyed gannets are now a common sight on Bass Rock, serving as a reminder of the devastation that was caused by bird flu.
“It’s reassuring that this research has found that these survivors are breeding just as successfully as other gannets.
“However, the slow rate of recovery is deeply concerning, particularly when considered alongside the growing threat to seabirds from climate change and poorly sited offshore windfarms.
“Further action is urgently needed from the Scottish and UK Governments to ensure these special birds are protected, their populations can recover, and their future is secured.”
