Threats to Bats

Bats reproduce very slowly—females usually only give birth to one pup per year—and as a result, it is extremely difficult for them to recover from substantial population declines. Several major threats are causing significant losses to bat populations worldwide.

Habitat Loss

Forests everywhere are disappearing at an alarming rate, usually as a result of timber harvesting, urbanization, or clearing for agriculture. Many bat species use forests to roost or to forage for food, and so as these woodlands disappear, so too do the roosting sites and food supplies of these species. Other species roost in caves and are driven out by cavers, miners, or even tourists looking to snap a photo. It is vital that bats are not disturbed when roosting, so be sure to stay out of caves and plan building maintenance work when bats are absent from buildings (fall, spring, and winter) whenever possible.

A Little Brown Myotis in flight. Photo (C) Sherri & Brock Fenton

A Little Brown Myotis in flight. Photo (C) Sherri & Brock Fenton

This map shows the occurrence of white-nose syndrome or the causative fungus

This map shows the occurrence of white-nose syndrome or the causative fungus.

White-nose Syndrome

White-nose Syndrome (WNS), caused by a fungus called Pseudogymnoascus destructans (Pd), was first discovered in North America in late 2006. Believed to have been brought to North America from Europe by cavers, it has since spread rapidly from its landing site in New York State to 32 additional US states and seven Canadian provinces. The fungus spreads in cool, humid conditions and grows on the muzzle, ears, and wings of hibernating bats, causing them to wake up early and use up their nutritional stores before winter has ended. As a result, infected bats nearly always die of starvation or dehydration. In infected hibernacula (caves where bats hibernate), the mortality rate can be as high as 80%–100%!

In total it is estimated that WNS has killed approximately 10 million bats since 2006. The fungus was found in Ontario caves in 2009, and continues to spread west. The four species of bats that are endangered in Ontario all hibernate in caves and have been affected by the disease. Any bats that are lucky enough to survive hibernation in an infected hibernaculum do not show any sign of built up immunity in later years, and there is currently no treatment for WNS available. Researchers are in the process of testing several potential treatments, including the possibility of treating infected bats with ultraviolet light, as the Pd fungus has shown particular sensitivity to it. Until a treatment becomes available, preventing the spread of the fungus is critical.

The Little Brown Myotis, once Canada’s most common bat species, has been most affected by the spread of WNS and is now classified as ‘Endangered’ in both Canada and Ontario.

Wind Turbines

Since the late 1990s, bat carcasses have been found underneath wind turbines, and research has shown that these deaths most frequently come about via collisions with turbines or more commonly via barotrauma caused by the low air pressure around the turbine blades. The Hoary Bat, Little Brown Myotis, and Northern Long-eared Myotis are three of the species known to be harmed by wind turbines. Turbine-related deaths seem to increase during periods of migration or gathering for mating or foraging. There are many theories about why bats, who can see the turbines better than birds because of their ability to echolocate, are nonetheless attracted to the turbines. Studies are currently underway to determine the magnitude of the effect that wind turbines have on bat populations, but in the meantime, wind turbine companies, wildlife organizations, and governmental agencies are working to find ways to prevent turbine-related bat deaths. Some examples include increasing the turbine cut-out speed, utilizing GPS or radar tracking to locate approaching bats, or implementing a turbine “boom box” that emits a continuous, high frequency sound that disorients bats, deterring them from the area.

Wind turbines on a farm in Onatrio during sunset.

Wind turbines on a farm in Onatrio during sunset., Photo by Jason Ng on Unsplash

Pesticide Use

Pesticides have been shown to have negative effects on many insectivorous animals, and bats are no exception. Pesticides are sprayed on plants or insects, and then bats eat these insects, storing them in their fat stores until winter. During hibernation or migration, bats must utilize their saved fat stores. By this time, however, large amounts of pesticide can have accumulated in their stores, leading to pesticide poisoning. In winter, this can mean excessive burning of fat stores and immunosuppression, making poisoned bats more susceptible to infection with the fungus responsible for White-Nose Syndrome. Even if a bat is able to survive winter poisoning symptoms, they are often plagued with reproductive problems such as spring stillbirths.

For more information about threats to bats and specific response statements and recovery strategies for Ontario’s endangered bats, visit:

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