It has now been almost 10 years since white-nose syndrome, a devastating fungal disease of hibernating bats, was first found in Canada.

There are 19 species of bats in Canada, but not all of them are affected by WNS. Some bat species migrate south for the winter instead of hibernating, while others live in areas of Canada where WNS has not yet been found, such as Alberta, Saskatchewan and British Columbia. Sadly, WNS continues to spread west and is now found in Manitoba, as well as in all provinces east of Manitoba.

The Three Bat Species Affected

Three bat species in Canada have been severely affected by WNS:

  • Little Brown Bat
  • Northern Long-eared Bat
  • Tri-colored Bat

Researchers approximate that roughly six million bats in North America have died as a result of this disease. In areas of the Atlantic provinces, bat populations have declined by 99 per cent when affected by WNS, with similar trends in affected sites in Ontario and Quebec.

Other bat species develop the disease but for unknown reasons have been less severely impacted, including the Big Brown Bat and Small-footed Bat. But there is hope for impacted species: despite large-scale mortality, Little Brown Bats are persisting in Canada and even reproducing!

Despite large-scale mortality, Little Brown Bats are persisting in Canada and even reproducing. @Karen Vanderwolf

We caught this Little Brown Bat and her pup (shown nursing, above) in early July at a maternity colony in New Brunswick. This pup cannot yet fly, but its mother can fly while carrying a pup that is almost as heavy as she is!

At birth, a Little Brown Bat pup weighs about 30 per cent of its mother’s body weight. This maternity colony was found in a bat house, but maternity colonies can also be found in attics; the female Big Brown Bat pictured below was found in an attic in Ontario.

Maternity colonies can also be found in attics; this female Big Brown Bat was found in an attic in Ontario. @Karen Vanderwolf

Finally, Some Good News!

I surveyed bat colonies during the maternity season (late May, June and early July) in Ontario, Prince Edward Island and New Brunswick. I did this with help from Jordi Segers (Canadian Wildlife Health Cooperative National office) and Tessa McBurney (Canadian Wildlife Health Cooperative Atlantic office), among others. All the bats we caught appeared healthy. Most of the females were reproducing, even though WNS has been present for years in these provinces. The Canadian Wildlife Federation’s tagging and tracking study in the Ottawa area found similar results.

Researching Bats

To collect the data we need to research bats, we first have to catch them. We use two types of traps to catch bats for the purpose of taking measurements and samples for research.

Mist Nets

The mist nets are the same ones used to catch birds. Pictured below are Big Brown Bats caught in a mist net in New Brunswick in June 2019.

Big Brown Bats caught in a mist net in New Brunswick in June 2019. @Karen Vanderwolf

Harp Traps

Below is an example of a harp trap that has been set up in front of an abandoned mine in New Brunswick during swarming season (August and September). Bats fly into the fishing line – which is strung in the frame like a harp – and then fall into the bag below. Swarming season is mating season for bats; they gather at potential hibernacula (overwintering sites), such as caves and mines.

Harp trap set up in front of an abandoned mine. @Karen Vanderwolf

During swarming surveys in Ontario, we were lucky enough to catch this beautiful male Red Bat in one of our harp traps! Red Bats are sexually dimorphic. This means the males and females don’t look the same – the females are not as brightly colored as the males. Red Bats are migratory and are not affected by WNS, however many migratory bats are killed by wind turbines during their migration south.


Sadly, the number of bats we caught during swarming season in New Brunswick was much less compared to our work pre-WNS. Although bats are reproducing, it will likely take a long time for the population to recover from the large-scale mortality caused by WNS.

What Can You Do?

Provide a roosting site for a female bat and her pup! CWF is here to guide you through every step. Begin by downloading these free DIY instructions. Building a bat house is always beneficial, but especially during the crucial months of April through June will provide a roosting site for a female bat to have her pup. Bats only have one pup per year, so providing them safe haven is vital to their survival. Bats also make great neighbours; they help control insects through spring and summer.

A Little Brown Bat maternity colony was living in this bat box. @Karen Vanderwolf

Learn more about Canada’s bats and how you can help them at