A new study has discovered evidence that Northern Gannets can recover from Highly Pathogenic Avian Influenza (HPAI) H5N1, with black irises indicating a previous infection. 

Scientists from multiple organisations investigated outbreak timings at colonies across their North Atlantic range. At their largest colony, Bass Rock, UK, a detailed study was conducted to estimate the impact of the virus on colony size, breeding success, adult survival, and whether Gannets were potentially able to recover from an infection.

Gannet exhibiting black iris (c) Jude Lane 2

Source: Jude Lane

Gannet exhibiting the distinctive black iris

Black irises – instead of the usual pale blue – were first seen in Gannets breeding on the Bass Rock in June 2022 with colour varying from completely black to mottled. The team took blood samples from 18 apparently healthy adult Gannets with both normal and black irises, which were tested for bird flu antibodies by APHA to determine whether the birds had been previously infected. Eight tested positive, of which seven had black irises. 

Black colouration

Dr Jude Lane, RSPB Conservation Scientist and lead author of the study, said: “This has been a fascinating development and the discovery may prove a useful non-invasive diagnostic tool. The next steps are to understand its efficacy, if it applies to any other species and whether there are any detrimental impacts to the birds’ vision. Ophthalmology exams will also be needed to determine what is causing the black colouration.” 


Source: Ashley Cooper (rspb-images.com)

Northern gannet Morus bassanus, killed by bird flu

High Pathogenicity Avian Influenza Virus (HPAIV) has negatively impacted wild and domestic bird populations globally for decades. However, the current strain (HPAIV H5N1) has seen shifts in both the timings of outbreaks and species affected - including seabirds. Northern Gannets appeared especially severely impacted, but there was limited understanding of how their populations were affected. 

High numbers of dead gannets were seen in Iceland during April last year followed by outbreaks in many Scottish colonies, Canada, Germany and Norway. By the end of June, outbreaks had occurred in five Canadian colonies and in the Channel Islands.


Source: Ashley Cooper (rspb-images.com)

Northern gannets Morus bassanus, killed by an outbreak of bird flu at Hermaness, Unst, Shetland

Outbreaks in 12 UK and Ireland colonies followed in a clockwise pattern with the last infected colonies recorded in September. Unusually high mortality was recorded at all but one of the 41 monitored colonies (75 % of the 53 North Atlantic colonies), and sampling data was available for 58% of these, all with dead birds testing positive. 

Largest gannet colony

To better understand the impacts of HPAI, the team further investigated Bass Rock in the UK. Bass Rock is the world’s largest Gannet colony, home to over 150,000 birds at their peak. The team calculated that adult survival between 2021 and 2022 was 42% lower than the preceding 10-year average. The full extent of how many birds died during that period won’t be confirmed until the birds come back this breeding season. 

The study was a collaboration between the RSPB, the University of Glasgow, the University of Edinburgh, Heriot Watt University and the Animal Plant Health Agency in partnership with the Scottish Seabird Centre. 

Gannet exhibiting normal iris (c) Jude Lane 1

Source: Jude Lane

Gannet exhibiting normal iris colouring

Susan Davies, CEO of the Scottish Seabird Centre said: “Like many northern gannet colonies across the North Atlantic the Bass Rock was severely impacted in 2022 by highly pathogenic avian influenza. Due to the long running research effort on the Bass Rock, it was possible to gain important insights into the changes taking place in the colony with a strong link emerging between virus infection and the changing iris colour in these striking seabirds and the high level of nest failure within the study area.” 

Seabirds are amongst the most threatened group of birds, out of the 25 species breeding here in the UK, 24 are Red or Amber on the UK list of Birds of Conservation Concern. The 2022 bird flu outbreak has provided another significant stressor to those already faced by our rapidly declining seabird populations. Quantifying and perhaps even mitigating its impact is therefore crucial to restore seabird populations.