Myotis sodalis
Indiana bat

Myotis sodalis, also known as the Indiana bat, is found only in North America. Their range spans from Iowa, Missouri, and northern Arkansas east to western Virginia and North Carolina, and north into New York, Vermont, New Hampshire, and Massachusetts. These areas include both their winter hibernation sites and summer ranges. Indiana bats hibernate in the northern reaches of their range in caves during the winter. In the summer and autumn months Myotis sodalis migrate to summer roosting sites. (Kurta, et al., 2002; Thomson, 1982)

Indiana bats hibernate predominantly in limestone caves, though some hibernate under the bark of dead trees. Cave temperatures range from 3.0 to 7.2 degrees Celsius; warmer temperatures are at the start of the hibernating season in October to November and cooler temperatures during March to April. They roost at elevations from 0 to 1,746 m above sea level (average 1047 m). During the summer, Indiana bats roost under the bark of large trees, under bridges, and sometimes in buildings. Trees in which Indiana bats are known to roost include bitternut hickory (Carya cordiformis), oaks (Quercus), elms (Ulmus), pines (Pinus), American sycamore (Platanus occidentalis), and eastern cottonwood (Populus deltoides). (Barclay and Kurta, 2007; Brack, et al., 2002; Butchkoski and Hassinger, 2002; Gardner and Cook, 2002; Tuttle and Kennedy, 2002)

Indiana bats are small, weighing approximately 7 g with a forearm range of 35 to 41 mm. They are dark grey or brown in color and their fur is considered soft. They are distinguished from other, similar, co-occuring members of M. myotis by their distinctly keeled calcar, a small cartilage projection from the foot, giving added stability to the wing. Indiana bat fur is soft in comparison to that of the very similar and closely-related little brown bat, Myotis lucifugus, which has fur that tends to be more shiny. Male and female Indiana bats are very similar with the female tending to be a little larger than the male. (Barbour and Davis, 1969; Whitaker and Hamilton, 1998)

Indiana bats are polygynous, with one male mating with multiple females. Males wait at the entrance to winter hibernacula for the opportunity to copulate with un-mated females. This occurs during the "fall swarming" period in October or November. There have been some accounts of Indiana bats copulating in late winter or early spring but this is rare. (Whitaker and Hamilton, 1998)

Myotis sodalis copulate in the fall, generally in late October. This is the time right before they enter into hibernation. Pregnancy does not begin at this time, as the females can store sperm over winter. This delayed fertilization allows the young to be born in summer (up to 68 days post fertilization). Females give birth to only one pup (on rare occasions twins) per year. Most pups are born between late June and early July with weaning at about 31 days (range 25 to 37 days). The first born of the season may be volant as early as mid-July. (Barbour and Davis, 1969; Barnard, 2009; Fenton, 1985; Whitaker and Hamilton, 1998)

Females provide care for pups after birth at summer roosting sites. Often maternity colonies are formed and male presence is rare. Females are responsible for providing nourishment for their pups through lactation. Time to weaning is about 31 days and pups are fully independent from their mothers in 2 to 3 months. (Whitaker and Hamilton, 1998)

Myotis sodalis individuals have been documented to live 20 years in the wild, but have an expected lifespan of 15 years in the wild. (Miller and Allen, 1928)

Indiana bats are social, which may account for their alternate common name, "social myotis." There have been no documented cases of social hierarchies within the species. Males and females hibernate together, but adults separate in the summer months. Maternity colonies contain juvenile males and only rarely adult males. They migrate seasonally; to travel from winter hibernacula to summer roosts Indiana bats travel distances up to thousands of kilometers. For example, a banded female caught by mist netting over a river in southern Iowa that had come from a hibernaculum in Missouri.

They have a wide nocturnal foraging area during the summer months. Perhaps this is why the area of suitable summer habitat does not correspond to population densities for this bat. For example, in a forest of up to 5 million hectares, population estimates were small as 10,000 bats. Another area of forest covering 1.7 million hectares was estimated to have 112,500 Indiana bats. (Gardner and Cook, 2002; Pierson, 1998; Whitaker and Hamilton, 1998)

Home range size of Indiana bats varies by individual as well as time of year. They are an average of 625 ha during the fall, and 255 +/- 89 ha in the spring. These home ranges are not defended. Perhaps the only territory defended is a space within a maternity colony or a hibernaculum, where bats might interact with individuals within 5 square meters of themselves. (Romme, et al., 2002; Whitaker and Hamilton, 1998)

Indiana bats, like other insectivorous bat species, use echolocation to maneuver through their various habitat types. They have well-developed eyesight which they use to aid with their travels from their winter hibernacula to their summer roosting sites. We can assume that Myotis sodalis individuals do communicate with each other using sound, but there have been no studies to further investigate this. Like other mammals, it is likely that these bats use chemical cues to communicate reproductive state. (Linzey, 2001)

Myotis sodalis individuals consume a diet of insects. A study found that Indiana bats eat insects from five main taxa: Coleoptera (beetles), Diptera (flies), Hymenoptera (bees, wasps), Lepidoptera (butterflies and moths), and Trichoptera (caddisflies). There are also differences in what females eat based on whether they are pregnant or lactating or neither. Lactating females eat greater amounts of coleopterans and trichoperans compared to non-lactating female bats. There are slight differences in diet based on location; southern colonies feed more on terrestrial insect species, whereas more northern bats fed on insects around wetlands. (Linzey, 2001; Murray and Kurta, 2002)

Predators of Indiana bats include carnivorous animals such as snakes, owls, raccoons (Procyon lotor), and other medium-sized mammals. The main adaptations Indiana bats have against predation is that they roost in caves and inaccessible tree crevices, putting them out of reach of many predators. They are also active at night and agile in flight. Myotis sodalis individuals hibernate in large clusters which help ensure survival (and warmth) between October and April. Their cryptic coloration also helps to protect them from predation.

Humans have been known to kill these bats, although they are not eaten. For example, at Carter Caves State park in Kentucky, two men clubbed 105 Indiana bats to death. Humans also unintentionally kill bats by destroying or cutting down summer roost trees or disturbing hibernation sites. (Hart, 2010; Mohr, 1976; Whitaker and Brack, 2002; Whitaker and Hamilton, 1998)

Indiana bats help control insect populations and are prey for bat predators. Indiana bats act as hosts for species of mites (Steatonyssus occidentalis and Macronyssus crosbyi) but there have been no documented intestinal parasites. Indiana bats have a direct impact on their cave environment by adding nutrients to the cave with their guano and decomposing bodies. (LaRoe, et al., 1995; Whitaker and Mumford, 1971; Whitaker, 1973)

Indiana bats may impact humans by helping to control pest insect populations. (Whitaker and Hamilton, 1998)

Indiana bats can become a nuisance in some places where their summer roots have been destroyed due to increasing human populations. Bats will then find their way into homes and attics to roost. Like most mammals in the United States, Indiana bats also may be carriers of rabies. However, documented incidence of rabies infection in Indiana bats is low. It is also very unlikely that humans will come into close contact with Indiana bats for the disease to be transmitted. If you come into contact with a bat or other wild mammals, you should see a doctor to receive immunizations that will protect you from this potentially fatal disease. (Butchkoski and Hassinger, 2002)

Indiana bats are a federally-endangered species and recovery plans are in place to monitor the health of this species throughout its range. For example, any organization intending to significantly alter a habitat within the range of this species is required by law to conduct surveys. If an Indiana bat roost is located within the area to be altered, plans must accommodate this individual (or group of individuals).

Temperate North American bats, including Indiana bats, are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. Currently, there is no known cure for white nose syndrome.

Humans also impact Indiana bats by entering their hibernacula for recreational caving. This can disturb bats while they are hibernating and cause them to wake up when there is no food available for them. Many Indiana bat hibernacula have been closed off to humans and a bat-friendly gate placed at the entrance to limit human intrusion. ("Indiana Bat (Myotis sodalis) Draft Recovery Plan: First Revision", 2007; Gargas, et al., 2009)