Gray Myotis: Myotis Grisescens

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Image of a hibernating gray bat

Physical Characteristics Of The Gray Myotis

The gray myotis/gray bat is the largest of the myotis (mouse-eared) bats, including the little brown myotis, the Indiana myotis, and the long-eared myotis of the North.

It is challenging to distinguish gray myotis from their myotis cousins. Gray myotises have grayer fur; most of the year, it is a uniform brownish-gray, turning in summer a light rusty brown. Tips of each strand contrast with the base; other myotises have bi- or tri-colored fur.

The ear and wing membranes of the Gray Myotis are gray to black. Wings attached to the ankle and not at the toes’ base are its key identifying features. On the inside curve of each claw, the gray myotis also has a distinct notch. ¹

Learn More: Cave Bats Of North America

Size Of The Average Gray Myotis

Length: 3 inches
Wingspan: 10-12 inches
Weight: 1/3 ounce

Gray Myotis Behavior

Gray bats are real cave bats, meaning they use caves for hibernation and summer roosts, but they don’t always return to the same cave every season. Hibernation requires an icy cave, limiting the number of suitable caves, resulting in only eight or nine caves for hibernation being used by 95% of all gray bats.

Due to the need for very warm caves near water, suitable summer cave roosts are also limited. These requirements for habitat mean that only 5 percent of the caves within their geographical range are appropriate. This is reflected in their patchy distribution and contributes significantly to listing these species within the Endangered Species Division of the US Fish and Wildlife Service.

Reproduction Of The Gray Myotis

Picture of a captured gray myotis bat

Males and nonreproductive females form reproductive female gray myotis form maternity colonies in the summer and bachelor colonies. Baby bats are born between early May and late June, depending on when females arrive at maternity roosts.

Single hairless young are born with their eyes closed and a complete complement of deciduous teeth; the birth weight is about 3 grams. Three to four weeks after birth, young begin to fly, but the growth rate depends on the roost temperature; in larger maternity colonies, the rate of growth is greatest.

The life span for gray myotis is about 14-15 years. ²

Gray Myotis Top 5 Predators

Snakes
Owls
Opossums
Raccoons
Crayfish (Feed On Dead Bats That Have Fallen From The Roost)

Habitats Of The Gray Myotis

Gray myotis bats are particular about what caves or cave-like habitats they prefer to live in. The roost site must have a mean temperature of 42 to 52 degrees F for hibernation. Most of the caves used for hibernation by gray bats have deep vertical passages with large rooms that function as traps for cold air.

Summer caves must be warm, with temperatures between 57 and 77 degrees F, or have small rooms/ domes that can trap roosting bats’ body heat. Normally, summer caves are located near rivers or lakes where the bats feed. It is known that gray bats fly as far as 12 miles from their colony to feed. ³

Gray Myotis Range In The U.S.

In the limestone areas of the southeastern United States, the gray bat occupies a limited geographic range. In Alabama, northern Arkansas, Kentucky, Missouri, and Tennessee, they are mainly found.

In northwestern Florida, western Georgia, southeastern Kansas, southern Indiana, southern and southwestern Illinois, northeastern Oklahoma, northeastern Mississippi, western Virginia, and western North Carolina, the gray bat is less commonly found. ⁴

Diet Of The Gray Myotis

Photo of gray bats roosting in cave

Myotis Grisescens forages over streams and reservoirs where night-flying aquatic insects are eaten. Gray bats rely on echolocation, like all microchiropterans, to locate their food.

The majority of foraging occurs within 5 meters of the water’s surface on which they feed.

Until recently, studies focusing on the diet of gray bats have not been conducted. Therefore, the data on this topic is preliminary. It’s still under debate whether gray bats are opportunistic or selective feeders. Recent studies indicate that this species feeds selectively, but more research is required.

It was originally believed that gray bats primarily fed on mayflies. Gray myotis bats have been observed feeding on large swarms of mayflies, but fecal analysis hadn’t shown evidence of the mayflies. Mayflies may be completely digested, so they wouldn’t appear in fecal research. ⁵

Prey Prefered By The Gray Myotis

Analysis of gray bat feces has shown that this bat species most often selects moths, flies, and beetles as prey. Other insects in the gray bat consist of:

Leafhoppers
Wasps
Spiders
Scorpionflies
Stoneflies

Threats To The Gray Myotis

Since gray bats are found year-round in caves, they are very susceptible to human disturbance. As with any cave bat, their populations have been negatively affected by modifications of caves and cave entrances.

Gray bat populations have also suffered losses caused by human-made impoundments from natural flooding and flooding. Gray bat populations may also be affected by pollution and siltation of streams, causing a reduction in aquatic insects and the overuse of pesticides.

Moreover, gray bats are prone to white-nose syndrome, a devastating disease that has caused unprecedented mortality in some of our hibernating bat species, particularly in the northeastern United States. ⁶

Sources:

Missouri Department Of Conservation. “Gray Myotis (Gray Bat).” MDC Discover Nature, nature.mdc.mo.gov/discover-nature/field-guide/gray-myotis-gray-bat. Accessed 5 Jan. 2021.
Best, Troy. “Gray Myotis.” Outdoor Alabama, www.outdooralabama.com/bats/gray-myotis. Accessed 5 Jan. 2021.
KBWG. “Gray Bat.” Kentucky Bat Working Group, biology.eku.edu/bats/graybat.htm. Accessed 5 Jan. 2021.
U.S. Fish and Wildlife Service. “Gray Bat (Myotis Grisescens).” U.S. Fish And Wildlife Service, 17 May 2019, www.fws.gov/midwest/endangered/mammals/grbat_fc.html.
Harriman, V. 2003. “Myotis grisescens” (On-line), Animal Diversity Web. Accessed January 05, 2021 at https://animaldiversity.org/accounts/Myotis_grisescens/
“Kentucky Department of Fish & Wildlife Gray Bat.” Kentucky Department of Fish and Wildlife, fw.ky.gov/Wildlife/Pages/Gray-Bat.aspx. Accessed 5 Jan. 2021.