WINNIPEG — Infectious disease and wildlife experts are scratching their heads over the recent discovery of a mass die-off of Canada geese in southern Manitoba, with some communities reporting carcasses found frozen in waterways.
Some of the deaths were linked to avian influenza, better known as bird flu, a contagious viral infection that affects hundreds of species.
While these particular infections are common in wild birds such as geese and ducks, it is rare to see a documented mortality rate, as a subtype of the virus called H5N1 was reported in Canada in 2021.
“We saw these mass deaths when it was first introduced, and then because it's been around for a few years now, we don't see as many deaths, probably because there's some immunity in the population now,” said Hannah Wallace, an infectious disease researcher at the University of Manitoba.
“It's a little strange that at this point in the history of this virus in North America … we're now seeing changes like this.”
The Canadian Wildlife Service said about 500 birds were found in Niverville, Man., a small town south of Winnipeg, with 200 of them captured last week.
On November 13, the city posted on social media that the virus had been detected in the geese population, having previously been detected in nearby communities.
On Monday, wildlife services received reports of another mass die-off, this time in Lockport, Man., north of Winnipeg.
Other areas affected by the same problem include Winnipeg, Portage la Prairie, Blumenort and places along the Red River between St. Andrews and Lockport, the agency said.
The Manitoba government said it is aware of recent wild bird deaths across the province and is advising people not to handle or take sick or dead birds.
The Department of Natural Resources tested 726 individual birds, and 54 were confirmed to be carrying the H5N1 strain of the virus, which can infect humans.
Health Canada says the risk of avian influenza remains low for most Canadians.
Since 1997, 900 human cases of the virus have been reported worldwide. The first human case of H5N1 infection resulting from transmission within Canada was announced in November 2024.
Most cases have resulted from close and prolonged contact with infected animals, such as people working in poultry production.
Wallace said scientists believe chickens or turkeys that contract avian flu often die because of differences in their immune systems compared to waterfowl such as geese.
Large groups of birds found dead in the province were located near open water bodies. The Canadian Wildlife Service said the highest number of reported cases occurred in the past few weeks due to warmer temperatures in October and November.
“Birds like Canada geese stay here until there's no food left in the agricultural fields or until they're forced to leave because they don't have open water,” said Frank Baldwin, a wildlife biologist with the agency.
“So they stayed very late this year, and it's likely the concentration of these birds really caused the virus to spread very quickly through what was left of the population.”
He added that Canada geese, which were late migrating, faced cold temperatures and a lack of food, which likely led to the mass die-offs seen recently.
Wallace said other factors, such as the age of the birds, mutation of the virus or whether the affected bird was also infected with another bacterial or viral infection, could also have contributed to the mass mortality.
She expects necropsies will be performed on some of the dead birds to answer some of these questions.
“It's a bit of a mystery at the moment, but we'll get to the bottom of at least some of it.”
This report by The Canadian Press was first published Dec. 10, 2025.
— With files from Daniela Germano in Edmonton.
