Daytime bat sightings in winter


A Western Long-eared Myotis from the 2010 Whistler Biodiversity Project survey. Photo: Bob Brett

In Whistler there have been at least two daytime sightings of bats flying during winter, which got us wondering: is this normal behaviour? Cori Lausen, who has researched bats in Whistler with the Whistler Biodiversity Project, says that while seeing bats in daytime during winter may be expected in moderation, excess activity can indicate something more sinister.


Even though most bats in B.C. are both winter hibernators and nocturnal (i.e., don’t typically fly during daylight hours) there are exceptions. Although researchers don’t yet understand why some bats do so, it can be normal to make a short trip out of their winter roosts. It could be that there are active insects to feed on, or an opportunity to mate, to drink water, or to stretch their muscles before returning to hibernation. Although these mid-winter flights typically occur at night, a few can occur during the day in some areas.


This activity is noteworthy because with so little known about where bats hibernate in B.C., it can help researchers narrow it down. It’s exciting to hear that bats may be hibernating in the area! Although many bat species find caves, mines, or rock crevices to shelter in during winter, some B.C. bats prefer to roost in large trees, especially those with peeling bark to hide behind, cavities in old growth trees or decaying snags, or the holes left by woodpeckers. Some will search for crevices in cliff bands, talus slopes, and even people's homes.

Although daytime bat activity during winter is interesting, if it noticeably increases, this may indicate an infection by white-nose syndrome (WNS) or other illnesses. WNS is caused by the non-native fungus Pseudogymnoascus destructans, which appears as a white powder growing in the airways of hibernating bats. The fungus infects the animal’s bare skin and scientists believe that it’s mostly transmitted through contact with other bats. The infection can cause excess activity when bats should be hibernating. This excess activity burns precious fat reserves, which in turn leads to bats flying during winter days in search of food and water, often resulting in the bat starving or freezing to death.


White-nose fungus has decimated bat populations in parts of North America, including eastern Canada where entire roosts of hundreds have been killed. Luckily the fungus has yet to reach western Canada—though it has been well recorded as close as Washington State.

Of B.C.’s 15 species of bats, eight can be found in Whistler. Some, like the Hoary Bat (Lasiurus cinereus), migrate south for the winter, travelling as far as Central America. .B.C’s hibernating bats enter a state of torpor in which their heart rate lowers to ~10 beats per minute and body temperature drops to near freezing. They can remain in that state for months during winter, or for just a few hours during a colder spring day. This ability to conserve energy at will is what affords them flight when their heart rate can go as high as 1,000 beats per minute.


If anyone finds an injured bat, they should leave it be and contact the Naturalists or bcbats.ca. Dead bats should be carefully collected wearing gloves and placed into a thick Ziploc baggie for government submission. At this time of year, it is particularly important to report any bats found dead or downed as they come out of hibernation, as this could be the only way of discovering if WNS has arrived in our province.


Written by: Jamie Marconi


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