Potential impacts of 2.3.4.4b highly pathogenic H5N1 avian influenza virus infection on Snow Goose (Anser caerulescens) movement ecology

Abstract

While wild waterfowl are known reservoirs of avian influenza viruses and facilitate the movement of these viruses, there are notable differences in the response to infection across species. This study explored differential responses to infection with highly pathogenic avian influenza in Snow Geese (Anser caerulescens) located in the California Central Valley. Though H5 antibody prevalence was high across years among birds sampled in the winter (75% in both years via hemagglutination inhibition), these values were even higher among birds sampled in summer that failed to migrate (i.e., August 2023 = 100% and August 2024 = 93% via hemagglutination inhibition). Birds that failed to migrate were also generally lighter than birds sampled in the winter and presented notable damage to cerebrum and cerebellum. In December 2022, a single individual positive for infection with H5N1 at the time of sampling indicated reduced movement during the 14 days following sampling but completed spring migration comparably with uninfected conspecifics. However, while no birds were actively infected during sampling and marking in 2023, two marked geese departed for migration late and one did not migrate at all. Additional banded birds marked in August have been reencountered in scenarios ranging from hunter harvest at a different site over a year later to found dead shortly after banding. Our data indicate that Snow Geese infected with HPAI have the potential to express variable outcomes following infection with highly pathogenic H5N1, ranging from rapid recovery within a migratory season to death. These data also suggest that the abnormal failure of some Snow Geese to migrate from the Central Valley is likely driven by HPAI infection.

Fig 1. Daily distance moved and daily minimum convex polygon (MCP) area for Snow Geese (Anser caerulescens) marked with GPS-GSM transmitters on a wintering area at Delevan National Wildlife Refuge (California, USA) on 15 Dec 2022.

Daily distance moved was calculated by finding the distance between each consecutive locational fix within a calendar day and summing this distance for each individual with at least 72 fixes (75% of possible fixes within a given day). The red line represents data from a single Snow Goose that was later revealed to have been naturally infected with HPAI and shedding virus at the time of marking.

Fig 2. Spring migratory paths for Snow Geese (Anser caerulescens) marked with GPS-GSM transmitters on a wintering area at Delevan National Wildlife Refuge (California, USA) on 15 Dec 2022.

Lines indicate migratory pathways while dots indicate the first location at the likely breeding site. The inset map shows the proximity of the identified likely breeding site of a single Snow Goose that was later revealed to have been infected with HPAI at the time of marking (red) relative to individuals that test negative for HPAI (blue). Basemaps are taken from the USGS National Map.

Fig 3. Unilateral focus of damage in the septum pellucidum of one of the 2023 snow geese.

A) GFAP immunohistochemistry. Note the large amount of dark brown staining in the black box which indicates increased numbers of astocytes (astrogliosis) as opposed to the opposite side. DAB chromogen. B) HE staining of the same focus characterized by mild vacuolation, loss of neurons, and prominent capillaries lined by plump endothelium.

Fig 4. Cerebellar folium of one of the 2024 geese.

A) GFAP immunohistochemistry. Severe astrogliosis characterized by the large amount of brown staining in the molecular layer and internal granular. DAB chromogen. B) HE staining of the same folium. The molecular layer is thin and rarified with decreased Purkinje cells and internal granular layer neurons.

Fig 5. Daily distance moved and daily minimum convex polygon (MCP) area for Snow Geese (Anser caerulescens) marked with GPS-GSM transmitters on a wintering area at Delevan National Wildlife Refuge (California, USA) on 7 March 2024.

Daily distance moved was calculated by finding the distance between each consecutive locational fix within a calendar day and summing this distance for each individual with at least 72 fixes (75% of possible fixes within a given day).

Fig 6. Spring migratory paths for Snow Geese (Anser caerulescens) marked with GPS-GSM transmitters on a wintering area at Delevan National Wildlife Refuge (California, USA) on 7 Mar 2024.

Lines indicate all movements from the initiation of migration through 15 June 2024 for all birds that migrated during a normal migratory window (blue), and those that migrated with a late departure (red). All movements from marking through 15 June 2024 for the non-migrating bird are shown in the inset map (green). Basemaps are taken from the USGS National Map.