White-nose syndrome has reached a cave near Fort Smith in Canada’s Northwest Territories, the northernmost-known hibernaculum for bats in North America. Biologists found bats carrying the fungus in May, and laboratory tests later confirmed the disease.
The 11-chambered cave shelters an estimated 3,000 bats and is home to little brown bats, big brown bats and northern long-eared myotis. Researchers did not observe the mass die-offs reported farther south, but they do not yet know whether the disease is newly established or spreading more slowly in the colder cave.
What the disease does to bats
White-nose syndrome is caused by the fungus Pseudogymnoascus destructans, or Pd. During hibernation, it attacks bats’ faces, wings and arms, prompting them to wake and groom themselves. That uses the fat and energy reserves they need to survive winter and can lead to dehydration or starvation.
The disease has killed more than 6.7 million bats in North America. In caves where it has spread, populations of little brown bats have fallen by 90% and northern long-eared myotis by 99%. Some little brown bat populations are slowly recovering, while the smaller northern long-eared myotis is considered particularly vulnerable because it has limited fat reserves.
How the fungus reached the northern refuge
White-nose syndrome was discovered in a cave at Fort McKay, Alberta, in 2025, nearly 200 miles south of Fort Smith. Biologists had expected more time to document healthy populations before the disease arrived, but found fungus on bats’ forearms and wings at the northern site in May.
Researchers also observed bats flying outside the cave in daylight, behaviour that can indicate illness or attempted recovery. One badly dehydrated bat found at a nearby lake could not fly; its wings were described as brittle, and the researchers believe it probably died later.
Why researchers have cautious hope
The fungus grows most readily at about 10C, while some chambers in the northern caves fall below freezing during winter. Researchers say Pd can still grow in those conditions, but potentially more slowly, which could produce a different outcome from the mass mortality seen in warmer caves farther south.
Scientists are also testing an experimental probiotic cocktail developed at Ontario’s McMaster University from microbes found on bats’ wings. Applied to summer roosts, the beneficial microbes are intended to spread among bats and slow Pd growth. Early field trials in British Columbia and Washington found that infected bats with the highest levels of probiotic microbes had the least Pd.
Wildfires add another pressure: fires in 2023 destroyed trees around the Fort Smith caves, reducing habitat and forcing bats to travel farther for food, summer roosts and mates. Researchers will return next spring to assess how the bats have fared and consider whether intervention is warranted.
No comments yet. Start the discussion.