As part of our commitment to the German northern gannet population, our team visited Heligoland again in May 2023. The devastating avian influenza outbreak of summer 2022 had cast a shadow over this visit from the outset - and unfortunately, our fears were confirmed. The avian influenza virus has clearly left its mark.
(c) Friederike Kremer-Obrock
Only about one-third of the northern gannets (Morus bassanus) returned to their nests in the spring of 2023. Many nests remained unoccupied; in some, one partner of these monogamous birds was waiting for the other, who will likely never return: avian influenza unfortunately carrying a high lethality rate.
(c) Friederike Kremer-Obrock
But there is another change. The returning birds regularly present with a grey-speckled or entirely black iris. Dark eyes instead of light grey to white. Since a large proportion of the northern gannets now exhibit these dark eyes, investigations were conducted confirming that this phenomenon occurs exclusively in infected and recovered birds with avian influenza antibodies in their blood, as detailed in a preprint study on northern gannets on Bass Rock, Scotland. However, the question of whether recovered birds are immune to H5N1 or whether they can be reinfected remains unanswered.
„Further investigations will follow,“ says Elmar Ballstaedt, station manager of Verein Jordsand on Heligoland, „We will be fitting northern gannets with dark eyes with transmitters and taking blood samples. We want to find out whether this strictly affects recovered birds and whether the animals alter their migratory routes.“
In average years, breeding success for northern gannets stands at 60%, whereas in 2022, only 14% of the chicks survived.
(c) Friederike Kremer-Obrock
Another question has been resolved, namely, whether the virus persists in the nests over winter. Samples indicated that the H5N1 virus was no longer detectable in the nests in spring. This is at least some positive news.
It now remains to be seen how the situation will develop in 2023. Dead gulls have already washed ashore in Cuxhaven, testing positive for avian influenza. H5N1 has not disappeared. Should the virus return to Heligoland, it would likely have catastrophic consequences for the depleted bird population. Northern gannets are particularly vulnerable here due to their very slow reproductive rate, and the absence of breeding-age birds in particular could threaten the local population of the species on Heligoland.
„In contrast to 2022, we are prepared and on alert. We know what actions to take should another outbreak occur. We cannot prevent it; we can only hope that the Lummenfelsen is spared this year. If so, the prognosis for the continued existence of the colony is good!“ says Elmar Ballstaedt.
(c) Friederike Kremer-Obrock
A further issue remains the entanglement of birds in plastic debris within their nests. The animals collect these plastics (primarily dolly ropes, the protective netting from bottom trawls) at sea and bring them to the island for nest construction. Another bird species, the common guillemot (Uria aalge), is now facing heightened risk, as they occupy the abandoned nests of northern gannets and likewise become entangled in the fishing lines. The first casualties are already hanging from the cliffs. Here, too, time will reveal the mortality toll among the common guillemots.
Summer 2023 on Heligoland thus begins with numerous uncertainties and the serious threat of the colony being struck once more by H5N1. Which bird species will be affected depends primarily on timing, as the common guillemots leave the cliffs for the sea with their chicks as early as June. There remains hope that it will not be as catastrophic as the previous year, and that the Lummenfelsen with all its biodiversity will be spared this year.
Source: High pathogenicity avian influenza (H5N1) in Northern Gannets: Global spread, clinical signs, and demographic consequences, May 2023, Jude V Lane, Jana WE Jeglinski, Stephanie Avery-Gomm, Elmar Ballstaedt, Ashley C Banyard; https://doi.org/10.1101/2023.05.01.538918.
