Despite ongoing presence of the avian influenza virus, no major outbreaks in 2024 yet

In recent years, we have repeatedly faced increased or even massive bird mortality among wild birds as a result of highly pathogenic avian influenza (HPAI). However, this was not the case in the first quarter of 2024. Although there were occasional indications that HPAI was still circulating among wild birds, there was little evidence of this in the field.

A total of 555 dead waterfowl were reported via the reporting portals of the Dutch Wildlife Health Centre (DWHC) and Sovon (Dutch centre of field ornithology), compared to 1,489 in the same period in 2023 and 2,855 in 2022. The species most frequently reported were Common Murre (86 individuals), Common Shelduck (56), European Herring Gull (45), Eurasian Woodcock (39), and Barnacle Goose (27). A relatively large portion of these, except for the Woodcocks, came from a regular reporter who specifically searches for dead birds along the north coast of the province Friesland and on the island Ameland.

Number of positive cases

From January through March 2024, 114 dead birds were collected for avian influenza research at Wageningen Bioveterinary Research (WBVR). Of these, 11 tested positive for HPAI H5N1. The rest tested negative (91 birds) or are still being investigated (12). The positive cases involved Barnacle Goose (5 out of 10 birds), Greylag Goose (2 out of 11), Mallard (1 out of 8), Canada Goose (1 out of 1), White-fronted Goose (1 out of 1), and Carrion Crow (1 out of 1). Notably, none of the 18 Mute Swans, 9 Black-headed Gulls, and 6 Common Buzzards tested positive. These species were heavily affected by avian influenza in previous years. A complete overview of the test results can be found on the DWHC website.

Situation in neighbouring countries

Compared to the previous two winters, the number of positive HPAI cases in wild birds and poultry in Europe was low this past winter. From January to March 2024, there were still clusters of cases around Denmark and northern Germany and in several Central European countries, but to the west and southwest of the Netherlands (where many of our migratory birds come from in spring), the situation was calm. This contributed to the Minister of Agriculture, Fisheries, Food Security and Nature’s decision on March 26 to largely lift the mandatory indoor confinement for poultry, which had been reinstated on November 14, 2023.

The upcoming period

The question currently occupying many bird and nature enthusiasts, (bird) researchers, and virologists is whether the upcoming breeding season will remain calm. The dramatic outbreaks among Sandwich Terns in 2022 and Black-headed Gulls and Common Terns in 2023 have shown that HPAI can spread rapidly among colony-nesting birds. Vigilance remains necessary, even if the current situation seems relatively quiet.

Please keep reporting

We would like to sincerely thank everyone who has taken the trouble to report or submit dead birds for research. Of course, reports remain welcome in the coming period. They provide us with indispensable signals about what is happening in nature.

Some recent publications

Knief et al. (2024) provided an overview of the mass mortality among Sandwich Terns in Northwest Europe in 2022. They reported 20,531 dead adult Sandwich Terns for the whole of Northwest Europe, amounting to at least 17% of the total Northwest European population. They indicated that this is likely an underestimate, as not all carcasses will have been found and reported. Moreover, they found that mortality was higher in colonies around the center of the distribution area (southern North Sea, including the Netherlands) than in the peripheral areas (Baltic Sea, Irish Sea, and Southwest France). They also noted that removing carcasses was associated with lower mortality rates in those colonies.

Tremlett et al. (2024) provided an overview of breeding bird counts of various seabird species in the United Kingdom in 2023, following the HPAI outbreak in 2021-2022. The most severely affected was the Great Skua. For this species, a decline of about 75% was recorded compared to counts before 2021. The number of territories at all surveyed sites combined dropped from 9,088 to 2,160; this count covered 81% of the pre-HPAI population. Declines of more than 50% were found at 79% of the surveyed sites.

Issue 2 of volume 125 of the magazine De Levende Natuur was dedicated to animal diseases. It included, among other things, an article about HPAI in mammals (Dutch). It stated that the virus has now been detected in the Netherlands in more than forty sick or dead individuals belonging to seven different mammal species. So far, there are indications in the Netherlands of some adaptations of the virus in infected wild mammals, but there is no evidence yet of transmission between wild mammals. The article emphasizes the importance of closely monitoring such infections and preventing them where possible. In another article about HPAI in wild birds (Dutch) in the same issue, it is stated that it is more important than ever to keep a close eye on signs of unusual bird mortality and to have a strategy ready.

Roy Slaterus, Sovon Dutch centre of field ornithology
Valentina Caliendo, Dutch Wildlife Health Centre

Sources

Knief, U., Bregnballe, T., Alfarwi, I., Ballmann, M. Z., Brenninkmeijer, A., Bzoma, S., … Courtens, W. (2024). Highly pathogenic avian influenza causes mass mortality in Sandwich Tern Thalasseus sandvicensis breeding colonies across north-western Europe. Bird Conservation International, 34, e6. doi:10.1017/S0959270923000400

Tremlett, C. J., Morley, N., & Wilson, L. J. (2024). UK seabird colony counts in 2023 following the 2021-22 outbreak of Highly Pathogenic Avian Influenza. RSPB Research Report 76.