GRAY BAT - Myotis grisescens
![[photo of gray bat]](images/graybat1.gif)
Large colonies of gray bats spend both the summer and winter in caves. Historical declines in gray bat populations were a result of human disturbance to maternity colonies and hibernation caves, loss of habitat, pesticides, and water pollution. Current populations are stable or increasing, and this species appears to be recovering. The gray bat is listed ENDANGERED by the Missouri Department of Conservation and ENDANGERED by the U.S. Fish and Wildlife Service.
Identification
The gray bat is the largest of all Myotis bats in Missouri, which includes the little brown bat, the Indiana bat, and the Keen's bat. The gray bat averages about 3 inches long and has a wingspan of 10 to 12 inches. It weighs about 1/3 ounce (a little more than a quarter). Gray bats have a uniform brownish-gray fur most of the year, but during the summer the fur turns a light rusty brown. The ears and wing membranes are gray to black.
Gray bats are difficult to distinguish from little brown bats and Indiana bats. The key identifying feature of the gray bat is that its wing is attached to the ankle and not at the base of the toes, as in all other Missouri Myotis bats. In addition, other Myotis bats have fur that is bi- or tri-colored, with the tips of each strand contrasting to the base. Gray bats have fur that is a single, uniform color. The gray bat also has a distinct notch in the tip of each claw.
For a technical description of this animal, refer to:Schwartz, C.W. and E.R. Schwartz. 1986. The Wild Mammals Of Missouri. University of Missouri Press. Columbia, Missouri. 356 pp.
Life History
![[line drawing of gray bat claws]](images/graybat2.gif)
Adult female gray bats enter hibernation caves in September and October and are soon followed by males and juvenile females. Gray bats hibernate in large, loose clusters across the ceiling and walls. Female bats emerge from hibernation in early March to mid-April, while males do not leave until mid-April or May. Gray bats also use other caves as rest stops as they migrate to their summer roosting caves. Winter and summer caves may range from a few miles to 200 miles apart.
Pregnant females roost in maternity colonies in caves separate from males and young females from late May to June. Each female gives birth to a single young in June. Young bats are able to fly four weeks later. Mothers and young rejoin the bachelor colonies in July and August. Gray bats exhibit great loyalty to their roosting and hibernating sites and will return to the same locations year after year.
Gray bats are active at night, foraging over water or along shorelines. They are insectivorous and eat a variety of flying aquatic and terrestrial insects. They may fly up to 12 miles from the roosting cave to the feeding area.
Habitat and Distribution
![[Missouri map of gray bat distribution]](images/momap.gif)
Gray bats use caves the entire year. Winter hibernation caves are typically vertical (pit) caves with cool, stable temperatures ranging from 42 to 52 degrees Fahrenheit. Summer caves are warmer (58 to 77 degrees Fahrenheit) with domed ceilings. The caves are usually found within two miles of rivers, streams, or lakes. Gray bats do not hibernate or roost in houses or man-made structures. Gray bats may require a corridor of forest vegetation between roosting caves and foraging areas. The forest cover provides cover from perdition during flight.
About 95% of all gray bats hibernate in eight caves, three of which are in Missouri. These caves are located in Shannon and Laclede counties. Missouri contains about 20% of the total population of gray bats. Most of the known gray bat caves are south of the Missouri River, particularly in the Ozarks, although a few exist north of the river.
Cause of Historic Decline
Unlike the Indiana bat, the gray bat remains in the Ozarks throughout the year and does not migrate to northern Missouri during the summer. Gray bat populations declined for many of the same reasons that have affected other bat species. Human disturbance to summer and winter caves, commercialization of caves, and pesticide contamination have contributed to the historical decline of the gray bat. In addition, because the gray bat utilizes caves near major rivers, reservoir construction flooded some important caves. Currently gray bats appear to be doing well, and populations are even increasing.
Current Threats to Gray Bats
- Human disturbance During the winter, gray bats hibernate and do not feed. Fat stored prior to hibernation is only enough to sustain the bat for about six months. Disturbing bats as they sleep causes them to use 20-30 days of stored fat. Since a bat's supply of fat is limited, excessive disturbance can greatly increase mortality. Disturbing bats in maternity caves during the summer can cause panicked flight. Females may drop or abandon their young, or desert the cave for a less suitable site.
- Cave modification Subtle changes in a cave's environment can adversely affect resident bats, who require specific temperature and humidity conditions. Building improperly designed gates and fences across cave openings can alter air flow, prevent access, and alter the temperature, humidity, and amount of light in the cave.
- Pesticides and pollution Gray bats depend on insects for food. Pesticide use may reduce the insect population in an area and affect local bat populations. Long-lived pesticides accumulate in gray bats when they eat contaminated insects. Changes in water quality resulting from stream channelization and bank modification, as well as pesticide contamination, can affect aquatic insect populations. Increased siltation, temperature changes, and decreased oxygen in the water may destroy or alter insect populations.
- Destruction of riparian areas During the summer, gray bats use wooded riparian corridors to move between their summer roosting caves and foraging areas. Timber cutting along stream banks not only destabilizes streams but may increase predation on bats.
Protection and Management: Steps Toward Recovery
Landowners can take the following measures to ensure the protection and survival of the gray bat.
- Do not disturb roosting or hibernating bats. Gray bats are easily disturbed in both their summer and winter caves. Avoid caves known to have hibernating or roosting bats. Respect signs, gates, and fences that warn visitors away from endangered bat caves. Do not build fires in or near a cave's entrance.
- Do not alter or modify caves Maintain a minimum of 20 acres of forested area around the entrance of a cave. Avoid removing or altering vegetation from a cave's entrance. If a bat cave is located on your property and you wish to construct a gate, please contact the Missouri Department of Conservation for technical assistance. Proper gate construction is essential in maintaining a cave's constant environment and to allow access to the cave by the bats.
- Reduce the use of pesticides Gray bats consume large amounts of insects and are potentially at risk to pesticide contamination. Reduce or avoid using pesticides around stream and riparian areas. Avoid pollution which may reduce insect populations and kill other aquatic animals.
- Maintain or establish wooded corridors along riparian habitats Gray bats need a forested corridor between roosting caves and foraging areas. The corridor of vegetation should be a minimum of 100 feet wide with a closed canopy. Young trees or seedlings can be planted along the corridor, and trees already present should be left standing or managed in a way that maintains a continuous closed canopy. Additionally, avoid removing vegetation from habitats along riparian habitats.
Missouri and federal law prohibits the importation, transportation, sale, purchase, taking, or possession of animals on the State or Federal lists. Damage of hibernation and roosting caves while bats are present is also prohibited.
For more information on gray bats, or to report sightings of this species, contact:
Endangered Species Coordinator or Wildlife Ecologist Missouri Department of Conservation Natural History Division P.O. Box 180 Jefferson City, MO 65102 573/ 751-4115
2/97
