The Indiana Bat

GAI bat biologists conduct surveys for rare, threatened, and endangered bat species and successfully help clients to avoid, minimize, or mitigate habitat impacts to satisfy state and federal agency requirements that protect these and other wildlife living within the vicinity of proposed projects. The Indiana bat (Myotis sodalis) is one such species, with a wide distribution across the Eastern and Midwestern United States.

Indiana Bat Facts

First found in southern Indiana’s Wyandotte Cave in 1904 and described to science in 1928, the Indiana bat was federally listed as endangered in 1967 under the Endangered Species Act (ESA). A species that is federally-endangered faces possible extinction within the foreseeable future throughout all or most its range.

Population records for the Indiana bat indicate a dramatic decline of about 50% in the last few decades. This is likely attributed to many factors, including habitat destruction. Also, because of their behavior of hibernating in large communal groups, Indiana bats are particularly susceptible to disturbance, vandalism, or adverse modification of hibernacula. The most recent threat to surface is a fungal disease called White-Nose Syndrome (WNS). First detected in New York in 2006, this disease has slowly but steadily spread south and west across the Eastern United States and Canada (in 22 states and 5 Canadian provinces) and has killed millions of bats, including Indiana bats.

The scientific name of Myotis (“mouse ear”) sodalis (Latin for “companion”) helps describe the physical and behavioral characteristics of this social, albeit often misunderstood, species. It is only “social” among its own kind, that is—for it has a habit of clustering in large groups (as many as 500 bats/sq. ft.) in caves and abandoned mines (hibernacula) during cold winter months.

Compared to other bats in the eastern United States, the Indiana bat is on the smaller end of the size spectrum, measuring in at 1.5 to two inches long and weighing only about ¼ ounce (about the weight of a house key or a few pennies). Studies indicate that Indiana bats live five to 10 years on the average, but some as long as 14 years.

Habits and Habitats

After several months of hibernation, the Indiana bat begins its annual spring migration to wooded or semi-wooded habitats. Male bats prefer to be alone or in very small groups; however, during summer months, pregnant Indiana bat females gather in maternity colonies of up to 100 individuals to roost and bear their young (called “pups”) under loose tree bark or in tree crevices, preferring dead trees in full sun for their warmth. Females only bear one offspring a year. At about one month old, each young bat is introduced to flight by soaring and swooping in tandem with its mother.

During autumn, Indiana bats congregate in caves (called swarming) to mate and to finish their summer/fall mission to accumulate life-saving fat reserves (energy) in preparation for winter hibernation. Although mating takes place during swarming, sperm is stored by females during hibernation until spring, when they will become pregnant and prepare for migrating to summer roost areas.

Having stored fat (their only energy source during hibernation), Indiana bats must wait out the winter in cool (ideally under 50° F) humid caves or mines that stay above freezing. Hibernacula with stable low temperatures to allow a reduction in metabolic rate and conservation of fat reserves are ideal; however, hibernacula with these ideal conditions are not equally distributed across the landscape. Therefore, individuals often travel hundreds of miles to hibernate collectively in groups that can range from a few to 50,000 bats.

Rare, Threatened, and Endangered Bat Studies

GAI conducts and coordinates studies for rare, threatened, and endangered species…especially bats. Across the Eastern United States, the federally endangered Indiana bat is one of the most frequently encountered species to arise during U.S. Fish and Wildlife Service (USFWS) reviews of proposed projects. Federally-listed species, such as the Indiana bat, are protected by the ESA from incurring unnecessary “take” (aka being killed, harmed, harassed, or otherwise negatively affected); therefore, projects that could contain habitat for the species must consider any potential effects that could arise. In support of proposed projects, GAI’s team of biologists perform environmental reviews, GIS habitat evaluations, spatial analyses, field habitat assessments, presence/absence surveys, reporting, mitigation planning, and agency coordination/consultation.

Our biologists conduct surveys and studies not only for the Indiana bat, but other bat species listed as threatened or endangered by USFWS and also by certain states. Although typically covered under the overall umbrella of Indiana bat surveys, GAI biologists must also consider other federally endangered bat species such as the gray bat (Myotis grisescens) and Virginia big-eared bat (Corynorhinus townsendii virginianus), which typically roost in caves year-round. Due to the devastating effects of WNS, the USFWS is also currently evaluating species such as the eastern small-footed bat (Myotis leibii), northern long-eared bat (Myotis septentrionalis), and little brown bat (Myotis lucifugus) for the possibility of federal listing under the ESA.

GAI biologists have extensive experience performing and coordinating studies for rare, threatened, and endangered bat species. Our qualified Indiana bat surveyors, Adam Mann and Jason Duffey, have a combined total of 20 years of bat experience and have managed, conducted, or volunteered on bat projects in most states across the range of the Indiana bat.

GAI’s bat experience includes the following studies, some or all of which could be involved in projects that could potentially contain suitable habitat for Indiana bats or other bat species:

  • Habitat assessments
  • Potential roost tree searches
  • Hibernacula/portal searches
  • Hibernacula/portal trapping
  • Mist netting presence/absence surveys
  • Acoustic presence/absence surveys
  • Radio-telemetry studies
  • Roost tree emergence surveys
  • Habitat mitigation
  • Indiana Bat Conservation Plans (IBCPs)
  • Protection and Enhancement Plans (PEPs)



Indiana Department of Natural Resources. Indiana Bats. Digital file accessed 2/5/2013.

U.S. Fish & Wildlife Service, Endangered Species. Digital file accessed 2/7/2013 (last updated 1/3/2013).

U.S. Fish & Wildlife Service News Release, May 17, 2012. Digital file accessed 2/20/2013.


Text Box: The U.S. Environmental Protection Agency has cited water runoff into our lakes, streams, ponds, and wetlands as a major source of pollution, accounting for 70% of all water pollution.
Share this post:

Learn More.