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All Aboard for Hibernation Station!

If you’ve heard of bears, you’ve probably heard of hibernation.


Hibernation is a type of dormancy. Dormancy is defined as the state of having normal physical functions suspended or slowed down for a period of time.


Hibernation is specifically caused by seasonal changes, often in weather and food availability. In most cases, it occurs over the winter, when the temperature drops and food is scarce. It can last for days or months, with some bear species hibernating for up to six months a year. There are two types of hibernation: obligate and facultative. Obligate hibernators, like echidnas, platypuses, and European hedgehogs, hibernate annually, regardless of temperatures and food availability. Facultative hibernators, like the black-tailed prairie dog, only hibernate when cold-stressed or food-stressed.



Along with seasonality, hibernation is identified by low body temperature, slowed breathing and heart rate, and low metabolic rate. Some body temperatures can drop as much as 32° Fahrenheit. Some animals, like bears, gorge on food during the summer months and gain a lot of fat storage to last through the winter. Others, like ground squirrels, will store food and occasionally wake up to eat. Certain animals will give birth during hibernation, while they’re resting. Every animal hibernates a little bit differently, with unique hangouts, eating habits, and bodily changes.



One animal that hibernates is bats. Not all bats hibernate; for example, Florida is warm enough that all bats living here are active year around. Some bats migrate rather than hibernate, traveling to warmer climates during the colder months. And some bats do both!


A great example of a hibernating bat is the Ussuri tube-nosed bat. Native to Russia, Japan, and North and South Korea, they are the only known bat species to hibernate in snow. These bats will tunnel into snowbanks, where they are protected from predators. These snowbanks may also provide a stable thermal environment and prevent water loss. The only other mammal that hibernates in snowbanks is the polar bear!


Photo by Yushi & Keiko Osawa, sourced from Bat Conservation International.


When bats hibernate, they choose to live in a place called a hibernacula. The hibernacula can be caves, mines, rock crevices, human made structures, and any place that maintains the right temperature and humidity. The bats are incredibly attuned to the environmental changes and gauge the changes in outside temperature through airflow at the entrance. Hibernaculums tend to be large, so that colonies of bats can roost together, and even mix species.


Wikimedia Commons image by Tim Krynak, USFWS.


When a bat enters hibernation, their heart rate drops from 200-300 beats per minute to 10 bmp. They can go minutes between breaths. Their body temperatures can drop 43-86°F, to close to freezing temperatures. All this effort reduces energy costs anywhere from 50-98%!


Some bats will hibernate for up to six to eight months, until the temperatures warm again and insects are active. Others will enter a daily torpor, and rest for a couple of hours to save energy. This daily torpor is similar to hibernation, with the major difference being length of time: a couple of hours to a day versus weeks and months at a time.


Photo by Craig Stihler/WVDNR


Daily torpor is used not only by cold dwelling species, but also the larger bats that live in high temperature environments, to cool down, save energy, and avoid predators. During their active period, these animals maintain normal body temperature and activity levels, but during their daily torpor, their metabolic rate and body temperature drop. When it gets colder here in Florida, our native bats will enter torpor. This keeps them warm and maintains their energy on the days where less insects are out and about.


Drops in body temperature have been shown to slow the reproduction rate of ectoparasites on bats in temperate environments.


Picture taken by Animal Keeper Anna Archer


One of the deadliest things affecting bats during hibernation is White Nose Syndrome. White Nose Syndrome (WNS) is a disease caused by a fungus that grows best in cold, dark, and damp places. The fungus, Pseudogymnoascus destructans or Pd, attacks the bare skin of bats, including their face, ears, and wings. Pd causes bats to be active when they usually wouldn’t be, meaning that they burn through their fat storage for winter. This leaves them weak or dying during a time where food is not available. Bats with WNS will often be seen doing uncharacteristic behaviors, like flying during the day in the winter.


Photo from Government of Alberta/Flickr, CC BY-ND


WNS was first identified in North America in 2007 and was expected to exist here from at least 2006. The Pd fungus has also been found in Europe and Asia, but bats in these areas have developed an immunity to WNS. It’s unknown how exactly the fungus got to America and American bats, but it is known that the spores of the fungus can exist on clothes for a long time. It is suspected that Pd was brought to America by spelunkers with contaminated clothes.


Map sourced from https://www.whitenosesyndrome.org/


Millions of bats have been affected by WNS. In certain areas, WNS has killed 90-100% of bats. The species most affected have been the Northern Long-eared bat, Little Brown bat, and Tricolored bat. Other species, like the Virginia big-eared bat, have been seen with Pd, but don’t usually show signs of sickness.


Photo from Ryan von Linden, NY Department of Environmental Conservation


Humans are the primary carriers of Pd. It is likely that cave explorers, spelunkers, and even state park visitors move the fungus from cave to cave. To mitigate the damage, certain caves require intense decontamination of clothing and equipment, entire new sets of clothes and equipment before entering, have closed to all visitors entirely, or have closed all together.


Picture sourced from http://travelguideromania.com/exploring-horizontal-caves-useful-tips-caving/


The best ways to keep bats safe from WNS are education, awareness, and following the advice and directions of experts and researchers as they learn. Learning about bats, their habitats, and their importance to their environment helps people to understand why these animals need to be protected from humans and diseases like WNS. Unfortunately, bats are highly misunderstood and the dangers of WNS are not fully acknowledged for the potential damage to the surrounding environment.


For more information about bats, White Nose Syndrome, and how people around the country are trying to help protect affected bats, check out https://www.whitenosesyndrome.org/


To all our batty friends out there, stay warm, stay sleepy, and stay fungus free!


Photos sourced from https://carnivora.net/-t2012.html

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