Bird flu present into the breeding season

Between mid-April and early May, there was an increase in reports of sick and dead Barnacle Geese as a result of infection with the avian influenza virus (bird flu virus). This mainly concerned birds that stayed behind at gathering sites in the eastern Wadden Sea area while their conspecifics continued their migration. Reports also came from the province of Flevoland and the west parts of the Netherlands. Although nowadays around 14,000 to 20,000 Barnacle Geese breed in the Netherlands, the majority of the 710,000 to 870,000 overwintering Barnacle Geese have departed in recent weeks for their breeding areas, which stretch from the Baltic region to Novaya Zemlya.

The Winter Outbreak

After ten relatively quiet months, wild birds in the Netherlands were once again affected by an outbreak of the highly pathogenic H5N1 virus last autumn. The Barnacle Goose was among the most vulnerable species. In the North Frisian outer-dike areas alone, more than 2,100 dead individuals were counted during the winter of 2024/25 by two observers who have been systematically recording bird mortality there for many years. Dead Barnacle Geese thus accounted for more than half (53.5%) of the total number of dead birds they found. They concluded that this figure likely represents a fairly accurate estimate of the mortality of this species in that area during the past winter season. Incidentally, mortality this past winter was lower than in the previous two outbreak winters, with 3,000 to 4,000 dead individuals in 2020/21 and 2,000 to 3,000 in 2021/22. Mortality due to bird flu and possibly other causes amounted to about 4–10% of the locally wintering Barnacle Goose population this season.

The full reported can be downloaded here.

Not only Barnacle Geese

The increased mortality due to highly pathogenic avian influenza (HPAI) in the Netherlands in recent months was most notable among Barnacle Geese, but the H5N1 virus was also detected in various other bird species. It mainly involved waterfowl (Mute Swan, Brant Goose, Greater Canada Goose, Greater White-fronted Goose, Greylag Goose, Egyptian Goose, Mallard, Gadwall, Common Eider) and laridae (Black-legged Kittiwake, Common Gull, Black-headed Gull, European Herring Gull, Caspian Gull, Great Black-backed Gull), but also waders (Sanderling, Red Knot, Ruddy Turnstone, Eurasian Curlew, Common Redshank) and birds of prey and other predators (Common Buzzard, Eurasian Goshawk, Eurasian Sparrowhawk, Common Kestrel, Western Barn Owl, Tawny Owl, Short-eared Owl, White Stork, Grey Heron).

Variants of the virus

Both the BB- and DI-variants of the H5N1 virus circulated, with the former mainly among gulls. In one Black-headed Gull, a highly pathogenic H5N5 virus was detected, which is rare in the Netherlands but, for example, is found more frequently in the United Kingdom (including in Northern Fulmars). Monthly updates on bird flu findings in dead wild birds in the Netherlands can be found here.

Please stay vigilant

Although the bird fly outbreak seems to be subsiding with the departure of overwintering waterfowl, vigilance remains necessary. Now that spring is in full swing, many colony-breeding birds such as gulls and terns have reclaimed their breeding sites. It is precisely in these places that the virus could spread again. Apart from a small number of reports of dead Black-headed Gulls, things still seem to be going well, but we certainly cannot breathe a sigh of relief yet. That is why we ask to stay vigilant. Reports of dead birds can be submitted to Sovon or our reporting form. Early detection of mortality is especially important for colony breeding birds. This allows for quicker action to be taken to reduce the spread of the virus.