INTRODUCTION
The Highly Pathogenic Avian Influenza A (HPAI) H5N1 virus of the A/Goose/Guandong/1/96 lineage emerged in Asia in 1996. Over the past 25± years, the viruses have continued evolving and have been detected across Asia, Africa, Europe, and North America (Ramey et al., 2022). There has also been an increasing number of mass mortality events involving wild birds (Verhagen et al., 2021). However, prior to 2022, no unusual mass mortalities caused by HPAIV had occurred in North America (Giacinti et al., 2024; Papp et al., 2017). The emergence of HPAI H5N1 virus clade 2.3.4.4b has marked a drastic turning point with morbidity and mortality among wild birds becoming increasingly common (Wille & Waldenström, 2023). The HPAI virus is now considered the cause of the largest avian panzootic outbreaks to date, based on the number of dead birds and species affected and the number and geographic spread of outbreaks (Klaassen & Wille, 2023).
Globally, H5N1 virus clade 2.3.4.4b has disproportionately impacted waterbirds, including cranes (Lublin et al., 2023; Pawar et al., 2023), Great Skuas (Stercorarius skua; Banyard et al., 2022), gulls and terns (Pohlmann et al., 2023; Roberts et al., 2023; Sobolev et al., 2023), gannets (Lane et al., 2024; Pohlmann et al., 2023; Roberts et al., 2023), Peruvian pelicans (Pelecanus thagus; Leguia et al., 2023), Cape Cormorants (Phalacrocorax capensis), and African Penguins (Spheniscus demersus; Roberts et al., 2023). In North America, this virus was first detected in wild birds in December 2021, following the observation of several wild gulls with neurological symptoms at a rehabilitation facility in St. John's, Newfoundland, Canada (K. Gosse, personal communication). One of these, a Great Black-backed Gull (Larus marinus), was the index case (Caliendo et al., 2022). During the following spring, mass mortalities involving thousands of wild birds were reported across eastern Canada, with the HPAI virus implicated as the cause.
Wildlife diseases that cause unusual levels of mortality or reduced fitness can exacerbate population declines when they interact with the cumulative effects of other natural and anthropogenic stressors, which may be especially true for marine birds (Phillips et al., 2023). Information on the scope and scale of unusual mass mortality events is crucial for assessing population-level impacts, and supporting conservation and management decisions (e.g., species status assessments and harvest management). However, robust assessments of mortality can be challenging to conduct, especially over vast areas. During large-scale mortality events, several types of surveys may be employed to estimate the number of affected animals, along with monitoring the temporal and geographic scope of the emergency. For coastal species, beached bird surveys are often conducted to estimate the number of birds affected by oiling and disease (e.g., Camphuysen, 1998; Haney et al., 2014). Aerial and boat-based surveys (Murphy et al., 1997; O'Hara et al., 2009) are also often employed to estimate wildlife mortality during environmental emergencies.
This study provides the first comprehensive collation and assessment of wild bird mortality for all reported species in eastern Canada during April–September 2022, following the incursion of HPAI H5N1 virus clade 2.3.4.4b into North America. Due to the unprecedented magnitude and geographic scale of the mortality, conducting systematic beached bird surveys to assess mortality was logistically infeasible. Instead, we combined data from federal, Indigenous, provincial, and municipal governments, the Canadian Wildlife Health Cooperative, nongovernmental organizations, universities, citizen science platforms, and reports from the public to develop a conservative estimate of the number of birds of various species that likely died during this disease outbreak. In addition, we present an analytical approach for identifying observations of mortalities which may have been reported by two or more different sources (i.e., double-counted birds). With this corrected dataset, we describe the magnitude of the unusual mass mortality event in terms of its magnitude, spatial extent, duration, and taxonomic diversity. In addition, by comparing estimated mortality numbers with population sizes and trends we make an initial assessment of whether biologically meaningful population-level impacts are likely for three prioritized species: Northern Gannet (Morus bassanus), which suffered significant mortality globally (Lane et al., 2024), and two harvested species, American Common Eider (Somateria mollissima dresseri) and Common Murre (Uria aalge), to support harvest management decisions.
METHODS
Study area and data sources
We defined eastern Canada as the provinces of Québec (QC), New Brunswick (NB), Nova Scotia (NS), Prince Edward Island (PEI), and Newfoundland and Labrador (NL), and our study period as April 1–September 30, 2022. To generate the best available estimate of reported wild bird mortality linked with HPAI during the study period, we collated reports of sick and dead birds on land, on the water, and on breeding colonies. Information on recovery rates for wild birds is limited, so we assume that birds reported as sick (i.e., those with clinical signs consistent with HPAI infection including tremors, lack of coordination, or lack of energy or movement) succumb to infection (Roberts et al., 2023). Hereafter, both sick and dead birds are referred to as mortalities.
Reports of mortalities on land and water were collated from numerous sources including federal, provincial, Indigenous, and municipal government staff and databases, the Canadian Wildlife Health Cooperative and other NGOs, academic researchers, and two citizen science platforms (iNaturalist and eBird; see Appendix S1 for detailed methods). Observations of wild bird mortalities on seabird colonies were gathered through direct solicitation from government biologists and academic researchers who obtained appropriate permits and authorizations. The reports included incidental observations made on any seabird colony and standardized surveys that were conducted by boat, foot, or air (both partial and complete). Unless reported mortalities were explicitly stated as having occurred on a colony, they were not classified as colony mortalities. All mortality data are publicly available (Avery-Gomm et al., 2024).
Each record included the species, date, number of mortalities, location information (i.e., site name or coordinates), observer information (name and contact information), and information source. We anonymized observer information in the published dataset. When species assignments were not provided, less specific taxonomic assignments were used (e.g., unknown gull, unknown bird). Taxonomic identification for iNaturalist reports was verified where the quality of the species identification was rated as “needs_id” by the submitter. When site names were provided instead of coordinates, coordinates were obtained using the GoogleMaps API in R version 4.2.2 (R Core Team, 2022). A subset of coordinates and site names were reviewed by regional experts to confirm the validity of this approach. To provide broad estimates for species groups, we classified species as either: seabirds, waterfowl, waders, shorebirds, loons, landbirds, or raptors. Age or breeding status was recorded when available. To assess how age class may be differentially represented in the mortality events, photos of Northern Gannets submitted to iNaturalist (557) were reviewed and the age class of birds was classified as adult, subadult, hatch year (HY), or unidentifiable. Similarly, photos of Common Murres were reviewed (61) and birds were classified as HY, after hatch year (AHY), or unidentifiable. We assumed that the age structure of birds in these photos reflects the age structure of birds reported off colonies. Mortalities of adult birds on colonies were assumed to be breeding adults.
Prioritized species
Environment and Climate Change Canada (ECCC), the federal wildlife management agency responsible for conserving migratory birds under the Migratory Birds Convention Act (1994), prioritized three species to support conservation and harvest management decisions in 2022. An overview of survey methods for Common Eiders, Northern Gannets, and Common Murres conducted in 2022 is provided below. Detailed information on surveys conducted for each species, including colony specific data, is publicly available (Avery-Gomm et al., 2024).
Common Eiders
Eastern Canada is the core of the breeding range for American Common Eiders (Beuth et al., 2016; Gutowsky et al., 2023; Lamb et al., 2019), hosting 85% of the global breeding population in three subpopulations: QC North Shore and NL (60% of breeding birds), QC St. Lawrence Estuary (20% of breeding birds) and NB & NS (5% of breeding birds; C. Lepage, unpublished data). The cryptic brown females of this species are responsible for raising chicks, and nest in colonies on hundreds of islands across the region. In the St. Lawrence Estuary of QC, the largest breeding colony (Île Bicquette) has been declining for the last two decades (Lepage, 2019). Other colonies in the St. Lawrence Estuary are stable or increasing (i.e., Île aux Pommes, Île Blanche, Île aux Fraises, Île aux Oeufs, Îles du Pot, and Île Laval; Giroux et al., 2021), as are the eider populations on the QC North Shore (Rail, 2021a). Elsewhere in eastern Canada, populations have been declining (Giroux et al., 2021; Noel et al., 2021). Colonies in the St. Lawrence Estuary currently support recreational harvests in the USA and Canada (Rothe et al., 2015) and are the subject of down collection (Joint Working Group on the Management of the Common Eider, 2004). An assessment of mortality and potential population impacts for this species was prioritized to support harvest management decisions.
To the extent possible, Common Eider colonies were surveyed by air or on foot throughout eastern Canada. In QC, this included surveys on foot of the three largest colonies in the St. Lawrence Estuary, by down harvesters between May 29 and May 31 (Île Bicquette, Île aux Pommes, Île Blanche). Twelve colonies along the North Shore of the Gulf of St. Lawrence were surveyed on foot by ECCC, between May 29 and June 22, as part of the quinquennial colonial seabird monitoring program, which includes nine migratory bird sanctuaries (e.g., Rail, 2021a). In NB, Machias Seal Island was partially surveyed weekly from mid-May to mid-August. An additional six colonies were incidentally surveyed in the Wolves and the Grand Manan Archipelagos by ECCC staff between May 31 and June 5, 2022. Six colonies along the northern peninsula of the island of Newfoundland (NF) were partially or incidentally surveyed on foot and by boat by ECCC staff between May 14 and June 7. In Labrador, nine colonies along the south coast were incidentally surveyed by air (helicopter) and on foot between June 6 and July 12, 2022. For NS, two colonies (Johns Island and Grey Island in southwest NS) were incidentally surveyed by boat and on foot by ECCC staff between April 30 and May 1, 2022. Complete aerial (helicopter) surveys of 18 other NS colonies were conducted by the Nova Scotia Department of Natural Resources and Renewables staff on June 21, 2022. No known colonies exist in PEI.
Northern Gannets
Canada hosts the entire North American breeding population of Northern Gannets (213,704 breeding birds) and 13% of the global breeding population, as of the latest assessment (Mowbray, 2020). Northern Gannets are long-lived seabird species that breed in dense colonies at three colonies in QC (Île Bonaventure, Rochers aux Oiseaux, and Île d'Anticosti) and three colonies in NF (Funk Island, Baccalieu Island, and Cape St. Mary's). Breeding populations at the five largest sites have increased dramatically since 1970 and are currently considered to be stable or increasing (i.e., from 2010 to 2020; S. Wilhelm, unpublished data).
In July and September 2022, ECCC flew aerial surveys of the two largest Northern Gannet colonies in QC (Île Bonaventure and Rochers aux Oiseaux) and all three Northern Gannet colonies in NF. Aerial photographs were digitized following standardized procedures (Chardine et al., 2013; Rail et al., 2014). The number of apparently occupied sites (AOS) and dead gannets were enumerated, in a complete survey of these colonies. Île d'Anticosti in QC has a very small population (192 breeding birds in 2019) and was not surveyed. In addition, complete surveys of three plots on Île Bonaventure were performed between June 18 and September 30, 2022. The Île Bonaventure colony and Cape St. Mary's colony are within provincial protected areas that are staffed during the summer months.
Common Murres
There are approximately 1.75 million Common Murre breeding in eastern Canada (Ainley et al., 2021). The majority breed in NF (1.5 million breeding birds), with smaller breeding populations in QC (191,500 breeding birds) and Labrador (76,228 breeding birds). The breeding population in NF and QC represents 19% of the North American population and ~10% of the global population (Ainley et al., 2021). Common Murre breed in colonies at 68 sites in eastern Canada, including 39 sites in QC, 12 sites in NF, 15 in Labrador, and 2 sites in NB. Eight of these colonies are considered large (>20,000 breeding birds): three are in QC (Île Bonaventure, Rochers aux Oiseaux, Sainte-Marie Island), four are in NF (Funk Island, Green Island, Cape St Mary's, South Cabot Island), and one is in Labrador (Gannet Islands). Common Murre are one of only two regulated harvested non-waterfowl marine species in Canada, and this species was prioritized for this assessment to support harvest management decisions.
In June 2022, the two small colonies on Machias Seal Island (NB) and Île à Calculot des Betchouanes (QC) colonies were completely surveyed on foot. An additional nine colonies were incidentally surveyed for evidence of mass mortality. In July and September 2022, the colonies on Île Bonaventure, Rochers aux Oiseaux, Baccalieu Island, and Funk Island were surveyed during aerial surveys of adjacent Northern Gannet colonies. Baccalieu Island was also incidentally surveyed on foot in August. In July, Gull Island and South Cabot Island were surveyed by boat and by helicopter, respectively. The colony at Cape St. Mary's was surveyed by boat and helicopter in July and by boat in September. In July, Great Island and Gull Island in Witless Bay Ecological Reserve (NL) were incidentally surveyed by boat.
Attributing mortality to the
A subset of sick and dead wild birds was tested for the HPAI H5N1 virus in eastern Canada between April 1 and September 30, 2022, as part of Canada's Interagency Surveillance Program for Avian Influenza Viruses in Wild Birds (96 species; Giacinti et al., 2024). Given that our objective was to quantify mortality for the purpose of supporting evaluations of population-level effects and that no other notable sources of mortality were reported for this period, we assumed that HPAI was a likely cause of all observed mortality for any species that tested positive for the H5N1 virus in sick and dead birds within our study region during our study period. For a description of the epidemiology of the HPAI outbreak in wild birds in Canada, including spatiotemporal dynamics, host taxonomic representation and viral genetic diversity see Giacinti et al. (2024).
For records where the species was unknown (e.g., unknown gulls), we presumed that mortalities were caused by the HPAI virus if ≥50% of the species within that group tested positive for the virus. For example, a bird identified as an “Unknown Gull” was likely one of any of the following species common in the study area: Herring Gull (Larus argentatus), Great Black-backed Gull, Ring-billed Gull (Larus delawarensis), Glaucous Gull (Larus hyperboreus), or Iceland Gull (Larus glaucoides). We checked if most of these species had tested positive for the HPAI virus at some point within the study area and study period, and if yes, we presumed that mortalities of unknown gulls were linked to HPAI (Giacinti et al., 2024). We did not presume records identified only as “Unknown Bird” were positive, and so mortalities for unknown birds were excluded from the HPAI mortality dataset, along with individuals that had a cause of death reported that could not be linked to HPAI (e.g., shot, window strike), and individual birds that tested negative for HPAI virus.
Scenario analysis to identify double-counted mortalities
Reported mortalities are subject to inflation when the same bird is reported by multiple observers, to multiple sources, or both (i.e., double counts). To address this issue, we conducted a comparative analysis aimed at identifying and mitigating instances of double counting within the HPAI mortality dataset. We presumed that records of a given species reported at similar times and places, might indicate duplicate. To assess this, we examined how the number of reported mortalities susceptible to double counting would be affected under six scenarios with varying levels of spatial and temporal overlap.
Specifically, the double count scenario analysis removed records from the complete mortality dataset as a function of the number of days between observations (±0 day, ±1 day, ±5 days), and the distance between observations (±1 km, ±5 km). The baseline scenario is the total reported HPAI-linked mortality with no records excluded and assumes no double counting. More precisely, each mortality record ai,j was coupled with another mortality record ai≠i,j, where i was a unique identifier for the record and j was the species. The distances (in kilometers) and the number of days between paired records were calculated and if the scenario conditions were met (e.g., for Scenario A, record ai,j fell within 1 km and 0 days of record ai≠i,j), the records were considered to be double counts. For each pair of records considered double counts, the record with the larger number of total observed birds was retained, and the other record was excluded. All retained records were iteratively resubmitted for consideration (i.e., coupled with another record within the dataset) until all records that met the scenario conditions were considered, and only records that did not meet the scenario conditions (i.e., non-double counts) and double counts with the highest number of total observed birds remained. Both records in a pair were retained only if the reports were made by the same observer to the same source. This exception reduced the mistake of excluding reports made in close proximity, as is typical during beached bird surveys. Analyses were conducted using R Statistical Software version 4.2.2 (R Core Team, 2022).
We assumed taxonomic identifications were accurate, only considering reports as possible double counts if the species' name matched. However, we acknowledge that some observers may have misidentified species (e.g., a Ring-billed Gull for a Herring Gull). To address this, we defined species groups for gulls, cormorants, and terns (see Appendix S2: Table S1), treating species within those groups as interchangeable regardless of the species or taxonomic resolution. For instance, paired reports of Arctic Tern (Sterna paradisaea), Common Tern (Sterna hirundo), and Unknown Tern were considered potential double counts if they met the spatial and temporal criteria. We excluded reports with other non-specific taxonomic assignments (e.g., unknown alcid) from the double count analysis because it was not reasonable to consider them to be interchangeable.
To obtain a double-count corrected estimate of total reported HPAI-linked mortality for each scenario, we excluded records identified as double counts and added all aggregated reported mortalities for species with less-specific taxonomic status (except for the cormorants, gulls, and terns) if those unknown species were presumed to be positive for HPAI. We then compared the total reported HPAI-linked mortality from the various scenarios with the total reported HPAI-linked mortality with no records excluded. To present spatiotemporal patterns and species-specific information about mortality, we used a double-count corrected estimate from one of the six scenarios. The scenario chosen represented a reasonable compromise between excluding double counts and retaining unique observations and was selected, based on consultation with experts who have experience with similar datasets and research questions.
Species-specific mortality estimates
We calculated species-specific mortality estimates by first removing records inferred to be unrelated to HPAI and then excluding records identified as double counts based on the chosen scenario. Mortality estimates were calculated by summing all records for a particular species. For the three prioritized species (Common Eider, Northern Gannet, and Common Murre), we present a more comprehensive spatiotemporal analysis of mortality events in the study area, with specific dates and events highlighted. It is important to note that the summed mortality numbers presented are conservative estimates, as we did not correct for unrecorded mortalities (e.g., areas not surveyed, birds not detected, birds not reported, birds lost at sea).
RESULTS
Reported mortalities
The complete mortality dataset includes reports of 47,580 wild bird mortalities across 142 species, as well as 23 less specific taxonomic assignments. Most of the mortality data were provided by governmental bodies. Staff from ECCC (28.6%), the Provincial wildlife management and natural resources departments of QC, NS, NB, PEI, and NL (18.8%), and municipal governments (10.9%) contributed most of the reported mortalities. Mortality data were also reported by staff from Parks Canada (2.0%), Fisheries and Oceans Canada (1.8%), and Indigenous governments in Labrador (Nunatsiavut Government, NunatuKavut Community Council) and the island of Newfoundland (Miawpukek First Nation and Qalipu First Nation) (0.04%). Researchers from academia provided 16.8% of the reported mortalities, while staff from nongovernmental organizations, notably the Canadian Wildlife Health Cooperative, contributed 7.8%. The reports of citizen scientists made to iNaturalist and eBird contributed 0.9% and 0.8% of reported mortalities, respectively. The remaining 11.6% of reported mortalities were made by members of the public directly to ECCC.
Scenario analysis
Our baseline HPAI mortality dataset includes 44,226 wild bird mortalities (93% of all reported mortalities), after removing records for 3354 mortalities that we did not attribute to HPAI. Across the scenarios, 5.9%–12.6% of reported mortalities were identified as potential double counts (Table 1). In the most restrictive scenario (Scenario A, ±0 day, ±1 km), 2610 birds were identified as potential double counts, and 5551 birds were identified in the least restrictive scenario (Scenario E, ± 5 day, ± 5 km). A comparison of scenario results indicates that the closeness in time criteria had a larger influence on the number of birds identified as double counts than the distance criteria. The two scenarios that used the ±5 day criteria (i.e., Scenarios C and E) identified the highest percentage of birds as double counts (11.0% and 12.6%, respectively). The two scenarios that used the ±0 day criteria (i.e., Scenarios A and D) identified the smallest percentage of birds as double counts (5.9% and 7.8%, respectively). Scenarios B (±1 day, ±1 km) and F (±1 day, ±5 km) were closest to the median percentage of records identified as double counts.
TABLE 1 Total number of HPAI-linked mortalities reported (i.e., baseline scenario) and the estimated number of mortalities with double counts removed according to a range of scenarios.
| Criteria | Baseline | Scenario A | Scenario B | Scenario C | Scenario D | Scenario E | Scenario F |
| Days | N/A | ±0 day | ±1 day | ±5 day | ±0 day | ±5 day | ±1 day |
| Distance | N/A | ±1 km | ±1 km | ±1 km | ±5 km | ±5 km | ±5 km |
| Total mortality | 44,226 | 41,616 | 40,391 | 39,344 | 40,771 | 38,675 | 39,561 |
| ∆ from baseline | 2610 | 3835 | 4882 | 3455 | 5551 | 4665 | |
| %∆ from baseline | 5.9% | 8.7% | 11.0% | 7.8% | 12.6% | 10.6% | |
| Including | |||||||
| Common Eider | 1937 | 1858 | 1894 | 1874 | 1857 | 1868 | 1892 |
| Northern Gannet | 27,957 | 26,277 | 25,669 | 25,292 | 25,787 | 24,806 | 25,028 |
| Common Murre | 9092 | 8716 | 8133 | 7652 | 8433 | 7552 | 8103 |
| Gull | 2378 | 2348 | 2326 | 2260 | 2330 | 2181 | 2260 |
| Cormorant | 997 | 990 | 981 | 959 | 988 | 948 | 950 |
| Atlantic Puffin | 364 | 299 | 282 | 244 | 259 | 276 | 238 |
| Black-legged Kittiwake | 260 | 257 | 251 | 227 | 252 | 224 | 245 |
| Razorbill | 127 | 121 | 119 | 109 | 120 | 107 | 118 |
| Tern | 83 | 80 | 74 | 75 | 80 | 74 | 74 |
Scenario B was chosen as the best estimate of reported mortality, to balance between excluding double counts and retaining unique records and mortality values presented in the remainder of the paper reflect estimates from this scenario. In Scenario B, most records identified as double counts occurred in NL (45.5%), QC (25.6%), and NS (24.2%), with smaller double counts occurring in the other provinces (Appendix S2: Figure S1). Most double counts were reports of Northern Gannets (63.9% of reports, representing 2737 birds) and Common Murres (22.4% of reports, representing 959 birds).
Spatial, temporal, and taxonomic patterns of estimated mortality
Accounting for double counts, we estimate that 40,391 bird mortalities across 45 species can be attributed to HPAI between April 1 and September 30, 2022 (i.e., Scenario B; ±1 km, ±1 day, Table 1). The first indication of a mass mortality event was detected in May when Common Eider colonies in the St. Lawrence Estuary reported significant numbers of dead breeding females. This was followed by exceptionally large numbers of mortalities in the southern Gulf of St. Lawrence among Northern Gannets and other species (e.g., gulls, cormorants, alcids). Very few mortalities in Newfoundland were in May and June. However, a second large wave of mortality began in July in eastern Newfoundland, with reports of Northern Gannets, Common Murres, and other species starting in the southeast (e.g., Burin and Avalon Peninsulas), and later along the eastern and northeastern Newfoundland coasts. Mortalities continued to be reported in across eastern Canada until mid-September, but reports of mortality along QC's North Shore, southwestern Newfoundland, and in Labrador were limited.
Seabirds and sea ducks accounted for 98.7% (39,863) of the estimated mortalities, with much smaller numbers of waterfowl (282, 0.7%), landbirds (133, 0.3%), raptors (97, 0.2%), and waders (16, 0.04%). Northern Gannets and Common Murres accounted for most of the estimated mortalities (63.6%, 25,669 and 8133, 20.1%, respectively). Smaller, but still noteworthy estimated mortalities were reported in gulls (2326, 5.8%), Common Eiders (1894, 4.7%), cormorants (981, 2.4%), Atlantic Puffins (Fratercula arctica, 282, 0.7%), Black-legged Kittiwakes (Rissa tridactyla, 251, 0.6%), Razorbills (Alca torda, 119, 0.3%), and terns (74, 0.2%). Among waterfowl, land birds, raptors, and waders, estimated mortalities were highest for Canada Goose (Branta canadensis, 107, 0.3%), American Crow (Corvus brachyrhynchos, 99, 0.2%), Bald Eagle (Haliaeetus leucocephalus, 43, 0.1%), and Great Blue Heron (Ardea herodias, 15, 0.04%), respectively.
Approximately 44% of estimated bird mortalities was observed on seabird colonies, and the remaining 56% of mortalities was observed elsewhere (on land or water). On-colony mortalities were dominated by Northern Gannets in QC (8669) and the island of Newfoundland (4899), with smaller mortalities of other species being reported on colonies in NB (963) and NS (643; Figure 1B). The largest estimated numbers of bird mortalities were reported on land and water in NL (8720 birds, including 101 birds in Labrador), although significant estimated numbers of mortalities were also reported in QC (7080), NB (4443), and NS (1542). Fewer than one thousand wild bird mortalities were reported on PEI (912).
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Summaries for prioritized species
Northern Gannets, Common Murres, and Common Eiders suffered mass mortality during the HPAI outbreak, and we provide an overview of the spatiotemporal distribution of the mortalities for these species. Similar information for gulls, cormorants, Atlantic Puffins, Black-legged Kittiwakes, Razorbills, and terns is provided in Appendix S3.
Common Eiders
An estimated 1894 Common Eider mortalities occurred in eastern Canada during our study period (Figure 2A). Most were breeding females at three colonies in the St. Lawrence Estuary: Île Bicquette (610), Île aux Pommes (503), and Île Blanche (222). These mortalities were reported during regular down harvesting operations, which entails complete surveys of the colonies, conducted in May and the beginning of June, as well as during follow-up surveys at the end of June. HPAI-linked mortality also occurred at several other smaller Common Eider colonies in the St. Lawrence Estuary: Île aux Fraises (66), Île Le Gros Pot (44), and Île Le Pot du Phare (4). Unusual mortality was also reported at Île La Razade d'en Bas (67), Île La Razade d'en Haut (10), Île aux Lièvres (53), and Île aux Basques (30). Surveys of other known eider breeding colonies in QC, NB, and NL conducted in May and June revealed no unusual mortality. In June, known breeding islands in NS were visited and no dead eiders were observed. Fewer HPAI-linked mortalities of eiders were reported off-colonies in QC (139). Much lower numbers were reported outside QC with 21 in NS, 13 in NB, 5 in NL (of which 2 were on the island and 3 in Labrador) and none reported in PEI.
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Northern Gannets
We conservatively estimate that 25,669 Northern Gannets died from HPAI in eastern Canada during our study period (Figure 2B). The highest estimated number of mortalities occurred in QC (18,242), followed by NL (13,646, including 101 for Labrador), NB (5406), NS (2185), and PEI (912). Approximately half the mortalities occurred on the five colonies that were surveyed (13,583), and half were reported on beaches and on the water (12,086). Out of 557 images of individual dead gannets submitted to iNaturalist, 92.8% were identified as adults. Another 3.2% were categorized as subadults based on the presence of black secondaries or tail feathers and it was not possible to identify the age of birds in the remaining 4% of images. Consequently, we assume that 92.8% of 12,086 dead gannets reported on beaches and on the water were adults (i.e., 11,216), and may have been breeding.
The largest gannet colony in Canada, on Île Bonaventure, hosts 50% of Canada's breeding population (~104,000 breeding birds; Rail, 2021b). Île Bonaventure is closely monitored and the first on-colony documentation of mortality was made on May 24, 2022, by an employee of Parc National de l'Île-Bonaventure-et-du-Rocher-Percé (J. -L. Legault, personal communication). A subset of these birds later tested positive for HPAI virus (Giacinti et al., 2024). Photographs taken during the first population aerial survey of the colony on July 11 revealed 1911 dead gannets. A second survey to evaluate breeding success was flown on September 19; however, due to the elapsed time between the beginning of the mortality event and the September survey, many birds were decomposed to the point of making enumeration of carcasses from photographs impractical. In addition, dead birds in three study plots were enumerated weekly between June 18 and October 10. The mortality rate in study plots peaked before July 30 but continued until the park closed October 10, 2022 (Y. Seyer, unpublished data). Only 1634 mortalities reported in plots between July 14 and September 30 are included in the mortality estimate for this colony, to avoid double counting carcasses enumerated from aerial photographs. In total, 3545 Northern gannet mortalities were counted on Île Bonaventure.
The dominant source of the Northern Gannet mortalities observed throughout the Gulf of St Lawrence is believed to be gannet colony on Rochers aux Oiseaux, north of Îles-de-la-Madeleine in QC. Rochers aux Oiseaux is a remote colony in the middle of the Gulf of St. Lawrence and hosts 25% of Canada's population of breeding gannets (~52,000 breeding birds; Mowbray, 2020; Rail, 2021b). The earliest documentation of an outbreak and mass mortality at this colony was from Transport Canada's National Aerial Surveillance Program on June 27. A total of 5119 dead Northern Gannets were enumerated from aerial photographs taken during that survey. As with Île Bonaventure, dead gannets were not counted during the September 19 aerial survey. It is likely that the estimated 4065 dead gannets observed on nearby beaches originated from this colony.
The second wave of gannet mortalities started in southeastern Newfoundland in July and lasted until the second week of September. Mortalities were detected at all three colonies in this region, which together host 25% of Canada's population of breeding gannets (Cape St. Mary's ~30,000 breeding birds; Funk Island ~22,000 breeding birds; Baccalieu Island ~7000 breeding birds; S. Wilhelm, unpublished data). The first Northern Gannet to test positive for the HPAI virus near a colony in Newfoundland was a subadult found by a fisher within 1 km of Cape St. Mary's on June 5 (E. White, personal communication). The first Northern Gannet on a breeding colony was reported by an employee at Cape St. Mary's Ecological Reserve on July 16 (C. Mooney, personal communication). An aerial population survey of the colony on July 29 detected 365 mortalities, and a subsequent population survey detected 1136 mortalities. We estimate that at least 1501 breeding Northern Gannet died at Cape St. Mary's (at least 5.0% colony mortality). It is likely that 1052 dead Northern Gannets reported on the southeastern coastline of Newfoundland originated from this population.
The colonies at Funk Island and Baccalieu Island are remote and the status of outbreaks was only evaluated during aerial surveys. The first aerial population surveys of the Funk and Baccalieu colonies on July 27 and July 24, respectively, enumerated only a limited number (149 and 13) of dead individuals on these colonies. Subsequent aerial surveys on Funk (September 15) and Baccalieu (September 14) revealed a much larger-scale die-off (3158 and 28, respectively). At the Funk Island colony, 3307 mortalities were observed (at least 14.4% colony mortality), while at the smaller Baccalieu Island colony, 41 mortalities were observed (at least 0.4% colony mortality). The 525 birds reported along the northeast and eastern shores of Newfoundland likely originated from these colonies. The timing of mortality from the colonies in Newfoundland indicate that most mortality occurred between late July and mid-September.
Common Murres
Across eastern Canada, an estimated 8133 Common Murre mortalities were attributed to HPAI during the study period (Figure 2C). The mortality event for Common Murres followed the same pattern as Northern Gannets, with HPAI-linked mortality being reported first in the Gulf of St. Lawrence followed by an outbreak in eastern Newfoundland. The highest estimated number of mortalities occurred in NL (5999, including 7 in Labrador), followed by QC (2009), NB (116), PE (5), and NS (4). The larger mortality event on the island of Newfoundland is consistent with the larger population (~1.5 million breeding birds) compared with the Gulf of St. Lawrence (191,500 breeding birds; Ainley et al., 2021). Most of the 61 images of Common Murres associated with iNaturalist mortality reports were AHY (86.9%). Only 3.3% were HY birds (i.e., post-fledge chicks), and 9.8% of images were unidentifiable. Consequently, we assume that 7049 of the estimated 8112 dead Common Murres reported off colonies were adults (86.9%) and may have been breeding individuals.
In the Gulf of St. Lawrence, mortalities were reported between late May and mid-August, with most being reported between June 20 and July 20 on the beaches of Îles-de-la-Madeleine. These birds likely originated from colonies in Îles-de-la-Madeleine including Rochers aux Oiseaux, which host ~54,000 breeding murres (Ainley et al., 2021). Smaller numbers were reported on the Gaspé Peninsula and in northern NB, near a large murre colony at Île Bonaventure (~80,000 breeding murres; Ainley et al., 2021). Although an estimated ~50,000 murres breed at colonies on the QC North Shore of the Gulf of St. Lawrence only few dead murres were reported in this area.
A second, larger wave of mortalities event started on the island of Newfoundland approximately a month later. Initial reports of mortalities came from the Burin Peninsula and Avalon Peninsula in southeastern Newfoundland. These birds likely originated from the colonies in the Cape St. Mary's and Witless Bay Ecological Reserves, which together host ~540,000 breeding Common Murres (Ainley et al., 2021). By August 2022, the outbreak progressed northwards, with birds reported on the Bonavista Peninsula and Bonavista Bay. At least some of these birds likely originated from South Cabot Island (~20,000 breeding birds), based on the recovery of at least one bird off the northwest coast of Bonavista Bay that was banded as a chick on South Cabot Island in 2018. This bird was recovered dead on Ship Island (49.0642, −53.5693) on August 4, 2022, and subsequently tested positive for the HPAI virus (Giacinti et al., 2024). Few murre mortalities were reported in southern Labrador (7). Only 24 mortalities in the complete mortality dataset were from colonies—no mass mortality was observed at any of the 11 Common Murre colonies that were surveyed in 2022.
DISCUSSION
The HPAI H5N1 2.3.4.4b virus is now considered the cause of the largest avian panzootic to date (Klaassen & Wille, 2023). Our study provides the first comprehensive assessment of reported wild bird mortalities in eastern Canada during the mass mortality caused by the HPAI H5N1 virus clade 2.3.4.4b between April 1 and September 30, 2022. To establish a conservative estimate, we collated data from multiple sources in a comprehensive effort to understand regional spatiotemporal and taxonomic patterns of mortality both on and off seabird colonies. We presented a scenario-based method for identifying and excluding observations that were potentially reported more than once by different observers or sources (i.e., double counted).
After the double-count analysis, we conclude that the HPAI virus is linked to the deaths of at least 40,391 wild birds between April 1 and September 30, 2022. To our knowledge, in North America, there has been no recorded infectious disease that has ever caused a comparable level of mortality across such a diverse range of bird species. The mortality reported here far exceeds mortalities associated with the 2014–2015 outbreak of HPAI in waterfowl in the prairies (Canadian Food Inspection Agency, 2016a, 2016b), or avian cholera outbreaks in prairie waterfowl (1977; Wobster et al., 1979), Arctic sea duck colonies (mid-2000s; Iverson et al., 2016), or Alaskan seabirds (2013; Bodenstein et al., 2015), although larger mortality events caused by marine heat waves have been reported (e.g., Piatt et al., 2020). There is no indication that wild bird mortalities on this scale (i.e., in the thousands) occurred during the study period on the eastern coast of the USA (Harvey et al., 2023).
Our approach for handling double-counted mortalities could be applied to support the assessment of mortality in any case where information from multiple sources is used. We found that between 5.9% and 12.6% of reported mortalities may have been reported by more than one individual or source, highlighting the importance of accounting for double counts during large-scale data collation exercises. Although, mortality estimates from scenarios that remove possible double counts may be more accurate than the baseline scenario, they still fall short of capturing the complete picture because not all dead birds are reported and should be considered conservative.
In our study, Northern Gannets, Common Murres and Common Eiders suffered the greatest mortalities, followed by gulls, cormorants, Atlantic Puffins, Black-Legged Kittiwakes, Razorbills, and terns. Below, we discuss the potential for biologically meaningful population-level impacts for the three prioritized species: Common Eiders, Northern Gannets, and Common Murres. Given the size of the breeding populations for these species in eastern Canada relative to the number of mortalities reported, population-level impacts are certainly possible and even likely for Northern Gannets throughout their Canadian range, and for regional populations of Common Eiders, but are not expected for Common Murres.
Common Eiders
A notable event occurred in the St. Lawrence Estuary in QC, where mass mortalities were observed, affecting the colonies at Île aux Pommes, Île Bicquette, and Île Blanche. These three colonies represent 58% of the breeding population in the St. Lawrence Estuary and 11% of the breeding population of Common Eiders in Canada, and the United States (Lepage, 2019; C. Lepage unpublished data). When compared with their colony sizes in the previous summer (2021; 4619, 3263, and 3155 nests attended by a single female; C. Lepage unpublished data), the HPAI outbreak resulted in 10.9%, 18.7%, and 7.0% mortality, respectively. Cumulatively, the estimated number of mortalities at these three islands represents a 12.1% loss of breeding females from these three sites during early incubation. As a result of the mortality event, we expect the number of young birds produced to have been particularly low in 2022, and the population to be lower in the coming years.
Given that breeding colonies in the St. Lawrence Estuary support recreational harvests and the collection of eider down, this species was prioritized to support harvest management decisions. After considering the potential population level impacts of HPAI-linked mortality, population trends, and harvest pressures, ECCC's Canadian Wildlife Service—the agency responsible for hunting regulations in Canada under the Migratory Bird Act—recommended “a voluntary reduction in eider harvest for the 2022–2023 season and that hunters refrain from harvesting female common eider or young” (Environment and Climate Change Canada, 2022a). Changes to the migratory bird hunting regulations aimed at reducing the impact of the harvest on the Common Eider population in QC were deemed infeasible due to the brief time between the assessment of the mortalities on colonies and opening of the hunting season. Therefore, it was anticipated that raising awareness among hunters would suffice to mitigate the risk of an excessive population decline. ECCC also engaged with U.S. States agencies responsible for managing Common Eider hunting to relay the message about voluntary restriction to local hunters (e.g., Maine Department of Inland Fisheries & Wildlife, Massachusetts Division of Fisheries & Wildlife; C. Lepage, personal communication). Ongoing annual nest monitoring at eider colonies in the St. Lawrence Estuary will facilitate the assessment of the long-term impacts of HPAI mortality on these populations.
Outside of the St. Lawrence Estuary, no other major mortality events were reported in Comon Eider colonies. Although colonies on the North Shore of QC, and in NS, NB, and NL were only incidentally surveyed we are reasonably confident that no mass mortality events occurred outside the St. Lawrence Estuary. This is fortunate because eider populations in NB and NS are declining for reasons that are not fully understood (Giroux et al., 2021; Milton et al., 2016; Noel et al., 2021). It is worth noting that Common Eider mortalities were also reported in Maine (10), Massachusetts (19), and New Hampshire (1), and subsequently tested positive, between June 24, 2022, and July 25, 2022 (USDA, 2023), but no mass mortality events at colonies were reported (Harvey et al., 2023).
Northern Gannets
HPAI-linked mortality was observed at all five of the surveyed colonies. The second and fourth largest colonies, Rocher aux Oiseaux and Funk Island, appear to have suffered massive outbreaks, while the outbreak at Île Bonaventure, the largest colony in North America, was comparatively less dramatic. Direct counting of dead gannets indicated a smaller proportion of the Île Bonaventure breeding population died of HPAI (at least 3.4% colony mortality) than at Rochers aux Oiseaux (at least 9.9% colony mortality), despite survey effort being greater on Île Bonaventure. Similar comparisons to estimate the proportion of the breeding population that died as a result of HPAI-linked mortality are not possible for Newfoundland colonies because the mass mortality event occurred after July, which is when populations are censused.
As large white birds with well-defined territories, gannets are among the easiest to enumerate from aerial photograph surveys (Chardine et al., 2013). However, it was challenging to enumerate carcasses during the second aerial surveys of QC gannet colonies because the mass mortality event was well underway prior to the first aerial survey in July. Therefore, estimates for these colonies should be considered conservative. On NF, the main mortality event occurred after the first survey and before the second survey, so mortalities were enumerated in aerial photographs from both surveys. This may have resulted in some degree of double counting of dead gannets on the colonies; however, we assess that the impact of this on our estimate is minimal.
If we presume that the 11,216 adult mortalities reported off colonies and the 13,583 Northern Gannets observed dead on breeding colonies were breeding individuals, the reported mortality represents a 11.5% loss of the North American breeding population. However, the true loss to the North American breeding population is likely much higher for several reasons. Many Northern Gannets were likely lost at sea (e.g., Pohlmann et al., 2023), particularly those that died in the waters off the northeastern coast of Newfoundland (i.e., Funk Island, Baccalieu Island), where the dominant currents would tend to advect birds away from shore (Wu & Tang, 2011). Efforts to estimate at-sea losses could support an improved mortality assessment. An analysis of changes in the number of apparently occupied territories (AOTs) on colonies before, during, and after the mass mortality event will be necessary to resolve the complete picture of population impacts from the HPAI virus. For example, while the number of mortalities enumerated at Rocher aux Oiseaux represents only 9.9% of the breeding population, a 58% decline in the number of AOTs was observed in 2022, compared to the previous survey in 2020 (J. -F. Rail unpublished data).
Since monitoring of Northern Gannet colonies began in 1970, populations have increased significantly (Chardine et al., 2013). Across all five main colonies, the North American population is increasing or stable (Rail, 2021b, S. Wilhelm unpublished data). A full assessment of the population-level impact of HPAI on the six Northern Gannet populations in eastern Canada, and how long populations will take to recover, is beyond the scope of this paper. Several factors will influence recovery, including the number of mature non-breeding individuals available to recruit into the breeding population, breeding success in subsequent years, immunity of survivors to future HPAI infection, and the cumulative impacts of natural and anthropogenic stressors that may have additive or synergistic effects with HPAI. In the coming years, serological research will play a crucial role in elucidating exposure rates, survival outcomes, and the duration of acquired immunity following infection (Giacinti et al., 2024).
Globally, Northern Gannets are listed as Least Concern because they have a very large range and a large population size (1,500,000–1,800,000 mature individuals; BirdLife International, 2023). However, Northern Gannets were impacted across their range, with an estimated 75% of colonies experiencing unusual mortality events (Lane et al., 2024). This includes marked declines in the number of breeding birds at key colonies in the UK (e.g., Bass Rocks, over 71% decline in June 2022 compared with 2014; Lane et al., 2024). To comprehensively understand the population-level impact of HPAI on gannets worldwide, a global assessment of HPAI-related mortality and an updated population estimate are needed.
Common Murres
In eastern Canada, Common Murres were the species with the second highest estimated number of mortalities (8133). We estimate that 7049 of these were adults and may have been breeding. This mortality represents less than 0.5% of the breeding populations, therefore, clear population-level impacts of HPAI-linked mortality in 2022 is not expected. However, the dominant currents near the largest murre colonies on the eastern and northeastern coasts of NF likely advect birds away from shore (Wu & Tang, 2011). If at-sea losses are significant, the total number of murres succumbing to HPAI may be severely underestimated based on reported mortalities. As with gannets, efforts to estimate at-sea losses in 2022 and population surveys at key colonies (i.e., those with large populations) in the years post-outbreak will support a better understanding of population level impacts for Common Murres.
Unlike Northern Gannets, no mass mortalities of Common Murre were observed directly on breeding colonies in eastern Canada. The lack of mortalities seen on colonies was surprising given that thousands of adult murre mortalities were reported on nearby beaches. Similar observations have been made in Europe (Germany; E. Ballstaedt, personal communication). Initially, we reasoned that murre mortalities may not be readily observed at the colony because most murres nest in packed colonies on rocky cliff ledges, and sick or dead birds had fallen into the water. However, on Funk Island and Rocher aux Oiseaux, murre and gannets breed in adjacent colonies on the plateau, but still no dead murres were observed. We speculate that murres leave the colony when sick and recommend against characterizing the magnitude of outbreaks among Common Murre based on mortality observed on the colony.
Common Murre are harvested in Newfoundland and Labrador, a culturally important practice in the province (Chardine et al., 2008). This species is numerous in eastern Canada and populations have been increasing in QC, increasing or stable in the island of Newfoundland, and declining in Labrador (Ainley et al., 2021). After reviewing abundance, population trends and the mortality data presented here, ECCC chose “not to change migratory bird hunting regulations to reduce the harvest of Murres in Newfoundland and Labrador during the 2022 to 2023 hunting season” (Environment and Climate Change Canada, 2022b).
Considerations for interpreting estimated mortalities
It is important to acknowledge two simplifications that were made in arriving at these mortality estimates. First, we attributed all mortalities to HPAI for species that tested positive for the HPAI virus in the study area during the study period, removing only those records where individual birds tested negative or when certain causes of death were indicated (e.g., shot, window strike). While species-specific HPAI virus test results are available from Canada's Interagency Surveillance Program for Avian Influenza (Giacinti et al., 2024), attempts to adjust mortality estimates yielded improbable results. For example, out of the 185 sick and dead Northern Gannets tested, 122 (66%) tested positive for the HPAI virus. However, if we attributed only 66% of estimated Northern Gannet mortalities to HPAI, this would suggest that 8727 adult Northern Gannets died of unknown causes. This is far above background annual mortality rates for adults of this species in North America (5% per annum; Chardine et al., 2013). Although attributing all mortalities to the HPAI for species testing positive during the study period may be simplistic, lacking evidence of another large-scale mortality factor operating at the same time, it remains a reasonable assumption. Moreover, this approach aligns with other studies assessing HPAI mortality (e.g., Pohlmann et al., 2023; Rijks et al., 2022).
The second simplification was the assumption that all sick birds die. This was necessary, as the status of birds (sick or dead) was not consistently reported. While some birds may recover from HPAI (Lane et al., 2024), even when they exhibit severe neurological symptoms (Taylor et al., 2023), most do not. The assumption that all sick birds died would only cause an overestimate of reported mortality if a large proportion of sick birds recovered. To our knowledge, recovery rates of seabirds' with HPAI are low (e.g., African Penguins; Roberts et al., 2023; L. Roberts, personal communication). Although these two simplifications could lead to an over-attribution of mortalities to HPAI, we are confident that our estimates still represent only a fraction of the total mortality resulting from the HPAI virus outbreak in eastern Canada.
There are several compelling reasons our mortality estimates are conservative and likely underestimate reality. Our estimates are based on reported observations of sick and dead birds across an area spanning five Canadian provinces and Atlantic coastlines across 15 degrees of latitude. It is likely that many bird carcasses were not observed or reported, even in areas of intensive effort. A considerable body of literature shows that detection rates and persistence probabilities for seabird carcasses on beaches are higher for large birds and white birds than it is for small birds and dark birds, and that beach type, weather, and degree of scavenging all influence detection and persistence (e.g., Fowler & Flint, 1997; Wiese & Robertson, 2004). It was beyond the scope of this study to generate an extrapolated number to estimate total carcasses based on these factors (i.e., grounding probability, detection probability, persistence rate) due to the sheer size and geographic scope of this outbreak.
Additionally, detection and reporting of mortalities is likely to be lower in areas with lower human population density. Preliminary drift modeling suggests that large numbers of gannet carcasses likely deposited on the North Shore of QC and on the shores of Île d'Anticosti (Avery-Gomm et al., 2023), but very few mortalities were reported in these areas, which are also very remote from large population centers. Therefore, low reported mortalities in remote areas (e.g., North Shore of QC and Labrador) may reflect low detection due to low human population density rather than low mortalities—especially given both areas have large breeding seabird populations. Finally, some jurisdictions faced capacity challenges in documenting numerous public reports, particularly at times when other pressing issues like wildfires demanded immediate attention, necessitating a relocation of resources.
In eastern Canada, almost all reported mortalities were among seabird and sea duck species that forage at sea. Among such species, sick individuals may have died at sea, and at-sea losses of these carcasses may comprise a significant fraction of total mortality. Experiments designed to assess at-sea loss in the context of large oil spills and chronic oil pollution have identified that temperature, scavenging activity, and body size are some factors that influence how long a carcass will float (Burger, 1991; Ford et al., 1996; Wiese, 2003). Carcasses that float for longer have a higher probability of washing ashore (i.e., grounding), but the probability of grounding is influenced by oceanographic conditions, wind (Bibby & Lloyd, 1977; Ford, 2006; Ford et al., 1987), and how far the carcasses must drift to reach shore (Martin et al., 2020).
The proportion of mortalities that were lost at sea during this outbreak remains unknown but is likely to be significant and may have varied regionally in eastern Canada. As previously mentioned, the dominant currents in eastern and northeastern Newfoundland (Wu & Tang, 2011) likely act in concert to transport many carcasses floating in that region offshore. In the future, adapting operational drift modeling tools originally developed for oil spill response (e.g., Paquin et al., 2020; Sutherland et al., 2022) could facilitate the estimation of grounding probabilities for simulated particles configured to drift like seabirds. Such information could be used to estimate at-sea losses, thereby improving mortality assessments for specific species.
Across eastern Canada, dozens of breeding colonies were completely, partially, and/or incidentally surveyed by government and academic biologists. While all available data on observed mortalities within colonies has been compiled, it is crucial to consider various factors when interpreting this colony-related data. The ability to detect mortality within colonies depends on factors such as the size of the outbreak, when and how a survey was conducted, and the traits of the species, including where they nest and how likely sick birds are to return to the colony. Mortality in surface-nesting species (e.g., gulls, terns, pelicans, cormorants, and gannets) is likely easier to detect than mortality in burrow-nesting species (e.g., puffins and storm-petrels) or among cliff-nesting birds (e.g., kittiwakes, murres and gannets at some sites; Appendix S3) which apparently have difficulty remaining on ledges when sick or dead. Additionally, differentiating between fresh dead birds and decomposing dead birds posed challenges when enumerating mortalities from aerial photographs, especially when colonies are visited multiple times (e.g., Northern Gannets). Ultimately, the absence of detections of sick or dead birds at the colonies should not be taken as evidence of absence of mortality, and colony-based mortality assessments will tend to underestimate mortality. Population surveys in subsequent years will be necessary to assess population-level impacts.
Reflections and recommendations
The One Health Approach, a collaborative and transdisciplinary strategy that recognizes the interconnection between human, animal, and environmental health, has guided Canada's HPAI response. Representatives from ECCC, the Canadian Wildlife Health Cooperative, provincial/territorial government agencies, other federal departments (Canadian Food Inspection Agency, Public Health Agency of Canada, Parks Canada, and Indigenous Services Canada), and Indigenous and academic partners have all worked together in this endeavor (Giacinti et al., 2024). In the case of the mass mortality event in eastern Canada, communication and collaboration were the cornerstone of the response. Significant efforts were made by all parties to support mortality data collation efforts, however, data quality varied across jurisdictions. The magnitude, duration, and geographic scope of the mortality in eastern Canada was unexpected and unprecedented for this region. Similar large-scale events have occurred across the globe in recent years, with seabirds being among the highly vulnerable to HPAI-related mortality (Wille & Waldenström, 2023). In all cases, estimating total mortality is a logistical challenge.
Beached bird surveys have become an international practice for documenting and monitoring the impacts of various sources of mortality (Camphuysen & Heubeck, 2001; Jones et al., 2023; Wilhelm et al., 2009). Given the apparent vulnerability of seabirds and sea ducks to HPAI and challenges with colony-based mortality assessments, standardized beached bird surveys could provide valuable information. If implemented in areas of anticipated disease outbreaks or in areas when outbreaks are detected early, Beached bird surveys could improve the enumeration of large mortality events by providing information on the onset, duration, and magnitude of HPAI mortality. Beached bird surveys could also provide valuable information on species composition and age classes as well as improve access to fresh carcasses for testing, necropsy, and early confirmation of HPAI. Where the resources to establish dedicated surveys are limited, band recoveries or citizen science data from iNaturalist (e.g., Bartolotta et al., 2023; Taylor et al., 2024) may provide alternative approaches for understanding the characteristics of a mortality event, but further studies are needed to fully appreciate their strengths and limitations.
CONCLUSION
Within months of the first positive detection of the H5N1 clade 2.3.4.4b virus in North America, it caused a mass mortality event of unprecedented magnitude and duration, killing at least forty thousand wild birds across 45 species in Eastern Canada. Most of the mortalities were among Northern Gannets, Common Murres, and Common Eiders, although unusual levels of mortality were also reported in gulls, cormorants, Atlantic Puffins, Black-legged Kittiwakes, Razorbills, and terns. Based on our assessment, it is probable that Northern Gannets and Common Eiders will experience biologically meaningful population-level impacts in eastern Canada. Based on this mortality assessment, population level impacts are not anticipated for Common Murres, due to their large breeding populations. We recommend that the breeding populations of these three species in eastern Canada be monitored closely in the years that follow to assess the long-term impacts of HPAI-linked mortality and support conservation decisions.
AUTHOR CONTRIBUTIONS
Conceptualization: Stephanie Avery-Gomm, Tatsiana Barychka, Matthew English, Robert A. Ronconi, Sabina I. Wilhelm, Jean-François Rail, Matthieu Beaumont, Tori V. Burt, Sydney M. Collins, Carina Gjerdrum, Megan E. B. Jones, Andrew Kennedy, Stéphane Lair, Gretchen McPhail, William A. Montevecchi, Gregory J. Robertson, Regina Wells. Data curation: Stephanie Avery-Gomm, Tatsiana Barychka, Matthew English, Jean-François Rail, Tabatha Cormier, Tori V. Burt, Sydney M. Collins, Jolene A. Giacinti, Jean-François Giroux, Megan E. B. Jones, Liam Kusalik, Stéphane Lair, Christine Lepage, Gretchen McPhail, William A. Montevecchi, Yannick Seyer. Formal analysis: Stephanie Avery-Gomm, Tatsiana Barychka. Funding acquisition: Stephanie Avery-Gomm. Investigation: Stephanie Avery-Gomm, Tatsiana Barychka, Matthew English, Robert A. Ronconi, Sabina I. Wilhelm, Jean-François Rail, Tabatha Cormier, Matthieu Beaumont, Tori V. Burt, Sydney M. Collins, Steven Duffy, Jolene A. Giacinti, Scott Gilliland, Jean-François Giroux, Carina Gjerdrum, Magella Guillemette, Kathryn E. Hargan, Megan E. B. Jones, Andrew Kennedy, Stéphane Lair, Andrew Lang, Raphael A. Lavoie, Christine Lepage, Gretchen McPhail, William A. Montevecchi, Glen J. Parsons, Jennifer F. Provencher, Ishraq Rahman, Gregory J. Robertson, Yannick Seyer, Catherine Soos, Christopher R. E. Ward, Regina Wells, Jordan Wight. Methodology: Stephanie Avery-Gomm, Tatsiana Barychka, Matthew English, Robert A. Ronconi, Sabina I. Wilhelm, Jean-François Rail, Tabatha Cormier, Matthieu Beaumont, Tori V. Burt, Sydney M. Collins, Steven Duffy, Jolene A. Giacinti, Scott Gilliland, Jean-François Giroux, Carina Gjerdrum, Magella Guillemette, Kathryn E. Hargan, Megan E. B. Jones, Andrew Kennedy, Stéphane Lair, Andrew Lang, Raphael A. Lavoie, Christine Lepage, Gretchen McPhail, William A. Montevecchi, Glen J. Parsons, Jennifer F. Provencher, Ishraq Rahman, Gregory J. Robertson, Yannick Seyer, Catherine Soos, Christopher R. E. Ward, Regina Wells, Jordan Wight. Project administration: Stephanie Avery-Gomm. Software: Stephanie Avery-Gomm, Tatsiana Barychka, Campbell Bowser, Liam Kusalik. Supervision: Stephanie Avery-Gomm, Kathryn E. Hargan, William A. Montevecchi. Validation: Stephanie Avery-Gomm, Tatsiana Barychka, Campbell Bowser, Liam Kusalik. Visualization: Stephanie Avery-Gomm, Tatsiana Barychka, Campbell Bowser. Writing—original draft: Stephanie Avery-Gomm, Tatsiana Barychka. Writing—review and editing: Stephanie Avery-Gomm, Tatsiana Barychka, Matthew English, Robert A. Ronconi, Sabina I. Wilhelm, Jean-François Rail, Tabatha Cormier, Campbell Bowser, Tori V. Burt, Sydney M. Collins, Jolene A. Giacinti, Scott Gilliland, Jean-François Giroux, Carina Gjerdrum, Liam Kusalik, Stéphane Lair, Andrew Lang, Raphael A. Lavoie, Christine Lepage, Gretchen McPhail, William A. Montevecchi, Glen J. Parsons, Jennifer F. Provencher, Ishraq Rahman, Gregory J. Robertson, Yannick Seyer, Christopher R. E. Ward, Jordan Wight.
ACKNOWLEDGMENTS
Numerous individuals and organizations have been instrumental in completing this research, and their collective contributions have played a pivotal role in shaping the research outcomes (Appendix S4: Acknowledgements). We extend our sincere appreciation to members of the public who reported sick and dead birds, rehabilitation centers who reported observations and contributed data, and provincial and municipal conservation officers and other staff who responded to calls throughout the course of the outbreak. We are indebted to the staff and members of the Innu Nation, the Miawpukek First Nation (MFN), the Nunatsiavut Government, the NunatuKavut Community Council, and the Qalipu First Nation for their support. Special thanks to Mike Brown, whose code facilitated the extraction of mortality reports from eBird and Transport Canada's National Aerial Surveillance Program, for conducting a fly over of Rocher aux Oiseaux. Funding for this research was provided by Environment and Climate Change Canada, NSERC, and Memorial University of Newfoundland.
CONFLICT OF INTEREST STATEMENT
The authors declare no conflicts of interest.
DATA AVAILABILITY STATEMENT
The mortality dataset, colony survey information, and code to reproduce the double count scenario analysis (Avery-Gomm et al., 2024) are available from FigShare: 10.6084/m9.figshare.24856869.v2.
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Abstract
In 2022, a severe outbreak of disease caused by clade 2.3.4.4b Highly Pathogenic Avian Influenza (HPAI) H5N1 virus resulted in unprecedented mortality among wild birds in eastern Canada. Tens of thousands of birds were reported sick or dead, prompting a comprehensive assessment of mortality spanning the breeding season between April 1 and September 30, 2022. Mortality reports were collated from federal, Indigenous, provincial, and municipal agencies, the Canadian Wildlife Health Cooperative, and other nongovernmental organizations, universities, and citizen science platforms. A scenario analysis was conducted to refine mortality estimates, accounting for potential double counts from multiple sources under a range of spatial and temporal overlaps. Correcting for double counting, HPAI is estimated to have caused 40,391 wild bird mortalities in eastern Canada during the spring and summer of 2022; however, this figure underestimates total mortality as it excludes unreported deaths on land and at sea. Seabirds and sea ducks, long‐lived species that are slow to recover from perturbations, accounted for 98.7% of estimated mortalities. Our study provides estimates of bird mortality, with Northern Gannets (
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Details
; Barychka, Tatsiana 1
; English, Matthew 2
; Ronconi, Robert A. 2
; Wilhelm, Sabina I. 3
; Rail, Jean‐François 4
; Cormier, Tabatha 5
; Beaumont, Matthieu 4
; Bowser, Campbell 5 ; Burt, Tori V. 6
; Collins, Sydney M. 6
; Duffy, Steven 3
; Giacinti, Jolene A. 1
; Gilliland, Scott 5 ; Giroux, Jean‐François 7
; Gjerdrum, Carina 2
; Guillemette, Magella 8
; Hargan, Kathryn E. 9
; Jones, Megan 10 ; Kennedy, Andrew 5 ; Kusalik, Liam 1 ; Lair, Stéphane 11
; Lang, Andrew 9
; Lavoie, Raphael A. 12
; Lepage, Christine 4 ; McPhail, Gretchen 13 ; Montevecchi, William A. 13
; Parsons, Glen J. 14 ; Provencher, Jennifer F. 1
; Rahman, Ishraq 9
; Robertson, Gregory J. 15
; Seyer, Yannick 16
; Soos, Catherine 17
; Ward, Christopher R. E. 3
; Wells, Regina 18 ; Wight, Jordan 9
1 Environment and Climate Change Canada, Wildlife and Landscape Science Directorate, Ottawa, Ontario, Canada
2 Environment and Climate Change Canada, Canadian Wildlife Service, Dartmouth, Nova Scotia, Canada
3 Environment and Climate Change Canada, Canadian Wildlife Service, Mount Pearl, Newfoundland and Labrador, Canada
4 Environment and Climate Change Canada, Canadian Wildlife Service, Québec, Quebec, Canada
5 Environment and Climate Change Canada, Canadian Wildlife Service, Sackville, New Brunswick, Canada
6 Department of Psychology, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada, Department of Biology, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada
7 Département des Sciences Biologiques, Université du Québec à Montréal, Montréal, Quebec, Canada, Société Duvetnor Ltée, Rivière‐du‐Loup, Quebec, Canada
8 Department of Biology, Chemistry and Geography, Université du Québec à Rimouski, Rimouski, Quebec, Canada
9 Department of Biology, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada
10 Canadian Wildlife Health Cooperative, Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada
11 Canadian Wildlife Health Cooperative, Faculté de médecine vétérinaire, Centre québécois sur la santé des animaux sauvages, Université de Montréal, St‐Hyacinthe, Quebec, Canada
12 Environment and Climate Change Canada, Wildlife and Landscape Science Directorate, Québec, Quebec, Canada
13 Department of Psychology, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada
14 Nova Scotia Department of Natural Resources and Renewables, Halifax, Nova Scotia, Canada
15 Environment and Climate Change Canada, Wildlife and Landscape Science Directorate, Mount Pearl, Newfoundland and Labrador, Canada
16 Environment and Climate Change Canada, Canadian Wildlife Service, Québec, Quebec, Canada, Department of Biology, Chemistry and Geography, Université du Québec à Rimouski, Rimouski, Quebec, Canada
17 Environment and Climate Change Canada, Wildlife and Landscape Science Directorate, Saskatoon, Saskatchewan, Canada
18 Environment and Climate Change Canada, Canadian Wildlife Service, Happy‐Valley Goose Bay, Newfoundland and Labrador, Canada