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Indiana bats on a cave ceiling.

Indiana bats on a cave ceiling. Photo by USFWS

Bat Facts Calendar



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Cave-hibernating bats start the year snug in their hibernacula (the caves and mines where they spend winter).  Hibernacula are quiet, dark, and cold. Probably not your idea of the ideal place to ring in the New Year, but just right for bats.
Why do bats hibernate in caves?  Many people think bats spend the winter in caves to stay warm, but it is more accurate to say they stay in caves to stay cold - - but not too cold.  The best hibernation caves are cold, but above freezing, and temperatures remain fairly stable throughout winter.
Can you imagine not eating for six months?  Most hibernating bats do not eat all winter – that’s an extreme weight loss plan!  They depend on stored body fat to survive during hibernation. 
Bats burn stored fat to survive winter hibernation.  During hibernation they lose 1/4 to 1/2 of their body weight.  An Indiana bat entering hibernation at 8 grams could lose 2 grams over winter and emerge in spring weighing 6 grams, about the same as 3 pennies.
Bats, like humans, are mammals and maintain a high body temperature – 98.6°F for humans and similar for bats. It takes a lot of energy to maintain high body temps. During hibernation, Indiana bats may drop their body temp to 40°F - 50°F, the same temperature as the cave, saving a lot of energy.
During hibernation, bats essentially stop producing body heat and, in turn, slow their metabolism, heart rate, and breathing rate to extremely low levels. At rest the heart rate of a bat is about 300 to 400 beats per minute. During hibernation, a bat’s heart rate can drop as low at 10 beats per minute.
Surveys to estimate the size of the Indiana bat population, an endangered species, are conducted every other winter, often in January. Here are results of recent Indiana bat hibernacula surveys.
The scientific name of the Indiana bat is Myotis sodalis. Sodalis means “companion.” The Indiana bat got this name because it is a very social animal – both in summer and winter they are found in colonies.
Indiana bats hibernate in tight clusters, up to 500 bats per square foot. For comparison, consider a standard 8½ by 11 inch sheet of paper, 325 Indiana bats could hibernate in an area this size!  No wonder they are called the “social bat.” See some photos of Indiana bat clusters.
Indiana bats look a lot like some other bats, especially the little brown bat.  How do bat experts tell them apart?  One way is to look at the hair on their toes!  Indiana bats don’t have as much hair on their toes and the hairs are shorter.  Here is a photo of an Indiana bat's toes.
If bats are disturbed during hibernation, they may arouse and become active. When bats become active, they use up much more stored fat than when hibernating. They may die if their fat reserves are used up before winter is over.

During hibernation Indiana bats must arouse every few weeks.  These arousals are natural and essential for bats to survive the winter.  But extra arousals caused by disturbance can be deadly.  A single arousal may cause an Indiana bat to use as much energy as 70 days of hibernation. Too frequent arousals can use up fat reserves before winter is over.
There are thousands of caves within the range of the Indiana bat, but few are used by large numbers of bats.  Caves that have the right temperature and humidity requirements are rare.
Indiana bats, because they hibernate in large numbers in only a few caves, are extremely vulnerable to disturbance. There are currently seven caves and one mine that have 20,000 or more hibernating Indiana bats.  Collectively these hibernacula support 70% of the population.
Large, complex caves that attract Indiana bats are also attractive to people. Many of the best bat caves have a long history of visitation by people. As early as the 1820s some caves with large numbers of bats were commercially developed for caving. Commercialization of caves became lucrative and over the next 100 years led to large declines in Indiana bat numbers.
When caves were commercialized in the 1800s and early 1900s, we did not know that winter disturbance harmed hibernating bats.  Now we know that the Indiana bat population likely once numbered in the millions and began to decline steeply because of cave commercialization.
Disturbing hibernating bats was not the only harm from cave commercialization. Owners added doors and gates to control access.  Sometimes, these structures blocked entrances so bats could not get in. Sometimes they altered airflow which, in turn, changed the cave’s air temperature, making it unsuitable for hibernating bats. 
Indiana’s Wyandotte Cave is a prime example of how commercialization changes a cave.  Wyandotte may have supported millions of hibernating Indiana bats.  But over a long history of physical alterations caused by human use, including construction of doors and gates, numbers of Indiana bats hibernating in the cave declined to 1,000 by the mid-1950’s.
The Indiana DNR bought Wyandotte Cave in 1966 and restored it for bats, including removing a stone wall and door that controlled human access. Good stewardship by the Indiana DNR allowed the Indiana bat population to recover.  In 2011, over 60,000 Indiana bats hibernated here, the largest known population.
Poorly designed cave gates can be bad for bats, but well-designed gates can be a help.  “Bat friendly” cave gates allow bats to fly freely in and out and do not alter airflow. At the same time they prevent people from disturbing bats during hibernation.   Bat-friendly gates!
The biggest threat to the Indiana bat is white-nose syndrome (WNS).  WNS is a disease infecting hibernating bats, including Indiana bats.  WNS has killed more than 5.7 million bats in eastern North America. In some hibernacula, 90 to 100 percent of bats have died.
White Nose Syndrome (WNS) has spread rapidly since it was first discovered during the winter of 2006-2007.  At the end of the 2014-2015 hibernating season, the presence of WNS or Pd were confirmed in 28 states and 5 Canadian provinces.   Map of a current WNS occurrences
White Nose Syndrome (WNS) is named for the white fungus that appears on the muzzle and other body parts of hibernating bats.  Not all bats with WNS have visible fungus.  Photos of bats with WNS symptoms
Bats with White Nose Syndrome (WNS) often behave uncharacteristically during cold winter months, like flying outside in daylight and clustering near the cave entrances.  Here is a video with more information on how WNS affects bats and what is being done.
What should you do if you find dead or dying bats, or if you observe bats with signs of White Nose Syndrome? Contact your state wildlife agency (many provide an online electronic reporting system), email the U.S. Fish and Wildlife Service at WhiteNoseBats@fws.gov, or contact your nearest Service field office to report your observations.  See additional information on what to do.
A newly discovered fungus, Pseudogymnoascus destructans (Pd), , has been shown to cause White Nose Syndrome (WNS). Scientists are studying how the fungus infects and spreads; searching for a way to control it. The U.S. Fish and Wildlife Service and partners prepared a National Plan to combat WNS.
The Indiana bat is the only endangered species that has died from White Nose Syndrome (WNS); an estimated 40,000 Indiana bats have died from the disease. The northern long-eared bat has been listed as threatened because of mortality due to WNS.
What species of bats has White Nose Syndrome (WNS) affected? In addition to the Indiana bat (an endangered species), the tri-colored, little brown, northern long-eared, big brown, and eastern small-footed bats have died from WNS.  Some species, including the endangered gray bat, have been found with the fungus that causes WNS but we have not yet confirmed mortality in this species. 
In New York, the state first affected by White Nose Syndrome (WNS), 72% of Indiana bats have died.  WNS has spread from New York to Indiana and Kentucky, the states with the largest hibernating populations of Indiana bats. Most hibernacula will be surveyed this winter which will give us a better understanding of how WNS affects our largest populations. 
When first listed as endangered in 1967, the Indiana bat population was estimated at nearly 1 million. Numbers then declined steadily and by 2001 the population was estimated at just over 300,000. However, the population then increased and by 2007 was estimated at over 450,000. The U.S. Fish and Wildlife Service was optimistic that Indiana bat could be removed from the endangered species list. Then, White Nose Syndrome struck.
Surveys for Indiana bats are being conducted this winter (2014 – 2015).  During the last survey (conducted in 2013) Indiana bats were found hibernating in 16 states.  States with the largest populations were Indiana (42% of the rangewide total), Missouri (26%) and Kentucky (12%). Here are survey results.

Last updated: December 12, 2016