Gray Bat
Myotis grisescens
Summary 2
The gray bat (Myotis grisescens) once flourished in caves all over the southeastern United States, but due to human disturbance, gray bat populations declined severely during the early and mid portion of the 20th century. At one cave alone, the Georgetown Cave in northwestern Alabama, populations declined from 150,000 gray bats to 10,000 by 1969. In 1976, M. grisescens was placed on the U.S. Fish and Wildlife Service’s endangered species list and put under the protection...
Conservation status 3
M. grisescens is considered endangered by both the United States Fish and Wildlife service, according to the Endangered Species Act, and the IUCN Red List. Although CITES does not list this species of bat on Appendix I, II, or III, it is difficult to see why.
Gray bats began encountering problems in prehistorical times when tribes of Native Americans began camping and living in the entrances of caves. The smoke from their fires likely suffocated the bats. It is also thought that they were placed in stews by Native Americans.
Guano was extracted from nearly every substantial gray bat cave in the south during the Civil War. This guano was used for gunpowder, not for fertilizer, as is commonly thought. It is thought that gray bat colonies suffered some of their largest losses during the Civil War. Studies of guano deposits in formerly occupied caves shows that gray bats (a highly resilient species) were able to prosper once again in spite of these losses.
Currently, the biggest threat to gray bat populations appears to be human disturbance at hibernation and maternity colonies. The bats in the maternity colonies do not tolerate disturbance, especially when flightless newborn young are present. Thousands of baby bats may be dropped to their deaths or abandoned by panicked parents. A colony will even completely abandon a cave in the presence of excessive disturbance. This is particularly bad because so few caves are habitable for gray bats. Starvation in the winter can also be a problem. When bats are aroused during hibernation, their important fat reserves are used up more quickly. If the disturbance is intense or frequent enough the bats may starve to death.
Despite once being one of the most abundant mammals of the southeastern United States, M. grisescens has been listed as an endangered species since 1976. In 1970 the population was estimated at 2.25 million bats after a census of 120 caves. However, a census in 1976 of 22 of the 120 caves found that these colonies had declined by an average of 54 percent each.
Other factors that influence the decline of Gray Bat populations are: vandalism, cave commercialization, toxins (like organochlorine pesticides, PCB’s, and lead), natural causes like cave-ins and flooding (killing bats and destroying important habitat), loss of caves by inundation by man-made impoundments, and reduction of insect prey over streams that have been degragaded by excessive pollution and siltation. (Arkansas Game and Fish Commission, 199; Clawson and Clark, 1989)
Improper gating at cave entrances also presents a problem. Gates must allow the airflow, temperature, humidity, and amount of light entering the cave to be the same as it was prior to the gate installment. Although steel bar gates do provide excellent protection from humans, these gates may be detrimental to bats by giving predators a place to perch and wait for bats to emerge. It has also been found that bats prefer to use un-gated entrances. The alternative, if possible, would be to put up a chain link fence topped with barbedwire around the cave. This would prevent humans from entering the bats' caves, and allow the bats to fly OVER the gate, rather than through it. This would also protect them from predators perched on the gates.
Due to protective increases at high priority colony sites, declines in M. grisescens populations have been halted in some locations, and others exhibit an increase in population. Currently there are about 1.5 million gray bats in existence. Important conservation measures that have been taken to aid in the stabilization of the population, especially the acquisition of caves by the U.S. Fish and Wildlife Service. This organization is currently in control of Blowing Wind Cave in northern Alabama. This is the most important summer cave for gray bats known. Fern Cave is the largest hibernaculum for gray bats and is also under the protection of the U.S. Fish and Wildlife Service.
Additional conservation measures are needed to help M. grisescens. The purchase and protection through proper gating and restricted use of other gray bat caves is very important. Education of spelunkers and other cave visitors who may unintentionally disturb the bats is key, as well as the continuation of federal efforts to reduce pesticide use (or at least limit their lifetime in the environment).
Temperate North American 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%. While there are currently no reports of Myotis grisescens mortalities as a result of white-nose syndrome, the disease continues to expand its range in North America.
US Federal List: endangered
CITES: no special status
IUCN Red List of Threatened Species: near threatened
Conservation status 4
Current Listing Status Summary
Status: Endangered
Date Listed: 04/28/1976
Lead Region: Great Lakes-Big Rivers Region (Region 3)
Where Listed: Entire
Population detail:
Population location: Entire
Listing status: E
For most current information and documents related to the conservation status and management of Myotis grisescens , see its USFWS Species Profile
Description 5
"Some 1.6 million gray myotis - almost the entire North American population - spend the winter together in the same nine caves, deep in hibernation. Some of them migrate long distances to reach these caves. Although 1.6 million sounds like a lot of bats, the total population has probably fallen by about 50 percent since 1965, and the species was listed as endangered in 1976. The bats depend on caves not only to hibernate, but also for summer maternity roosts. Hibernating bats can die if they are awakened when no food is available. Females need warm caves for maternity colonies, often choosing caves that have streams running through them, because the streams prevent some predators from entering the cave. The caves are always near a major river or lake, where they can forage for insects over water. Caves that are opened for tourism, vandalized, or flooded, are lost to the bats and so are caves that are sealed up, unless bat-friendly gates are installed. Awareness of the bats' needs seems to be helping halt the decline of gray myotis and some other cave-dependent species."
Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account
Habitat 6
Gray bats are restricted entirely to areas with caves or cave-like habitats. These caves are in limestone karst areas of the southeastern United States. Gray bats do not inhabit barns or other similar structures. This leads to extremely restricted nesting opportunities. Due to their requirement of unique cave types, Gray bats can only use 0.1% of available caves in the winter and 2.4% in the summer.
Ninety-five percent of the total Gray bat population hibernates in only eight or nine caves. Two are located in Tennessee, three in Missouri, one in Kentucky, one in Alabama, and one in Arkansas. The Arkansas hibernation cave houses about 250,000 Gray bats. The winter caves utilized by Gray bats have deep, vertical passages with large rooms that function as cold air traps. The temperature of these caves ranges between 6 and 11 degrees Celsius (42 and 52 degrees Fahrenheit).
As they are for the winter sites, gray bats are highly selective for caves providing specific temperature and roost conditions in the summer. These caves are warm, ranging between 14 and 25 degrees Celsius (57 and 77 degrees Fahrenheit). As an alternative to finding a cave within this temperature range, they can roost in caves with small rooms or dorms that trap the body heat of the roosting bats. Summer colonies of gray bats occupy a home range that often contains several roosting caves scattered along as much as 81 kilometers of river or lake shore. Banding studies have indicated that gray bats prefer summer caves that have a feeding area (river or other reservoir of water) not over 2 kilometers away. Despite this, they have been known to fly as far as 19 kilometers from the colony to feed.
Habitat Regions: temperate ; terrestrial
Other Habitat Features: riparian
Migration 7
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
Wintering caves often are hundreds of kilometers from summer range; Tuttle (1976) reported one-way migration distances of 17-525 kilometers. In some areas the same caves are used in winter and summer; in other areas (e.g., Missouri, Arkansas) many caves used in summer are vacant in winter. Most Florida breeders migrate north to hibernate in cooler caves of northern Alabama and central Tennessee; migration occurs mostly in September-October, some as late as November or December (Layne 1978), females preceding males. Females depart wintering caves in late March and early April, males in late April and May. Evidence suggests that bats migrate in small flocks (Barbour and Davis 1969). Small caves may be used as rest stops (Smith and Parmalee 1954).
Reproduction 8
Information on the mating system of these animals is sparse. They are reportedly polygynous.
Mating System: polygynous
Breeding in this species occurs shortly after the bats enter their hiberation caves. After entering the winter cave, the female gray bat is inseminated. Females exhibit delayed fertilization. After copulating, a female holds the sperm through hibernation. Fertilization of ova occurs when the female emerges from hibernation.
Females do not reach sexual maturity until they are two years old. For their size, bats are among the world’s slowest reproducing mammal.
Females give birth to a single offspring in June, after migration to the summer caves has taken place. The period between birth and weaning is two months. During these two months there is segregation between members of the colony. The adult females and their newborns roost in maternity caves. The adult males and yearlings of both sexes roost in bachelor caves.
By August, all the juveniles are flying (most are capable of flight 20-25 days after birth) and general mixing and dispersal of the colony occurs over the summer range.
The growth rates of young vary with the temperature at the maternity roosts. It has been discovered that young in warmer roost situations grow more rapidly.
Breeding interval: These animals breed once per year.
Breeding season: Breeding occurs in the fall, when the bats enter their winter caves.
Range number of offspring: 1 to 1.
Average weaning age: 60 days.
Average age at sexual or reproductive maturity (female): 2 years.
Average age at sexual or reproductive maturity (male): 2 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous ; sperm-storing ; delayed fertilization
Average birth mass: 2.9 g.
Average number of offspring: 1.
Average age at sexual or reproductive maturity (male)
Sex: male: 456 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 456 days.
As in all mammals, the mother provides milk to her growing young. Neonate gray bats are altricial. The mother attends to her young in a nursery cave. This is especially interesting, because the mother can locate her own offspring among the hundreds of baby bats which may be in the cave.
Parental Investment: altricial ; pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)
Range description 9
The range extends from southeastern Kansas and central Oklahoma east to western Virginia and western North Carolina, and from Missouri, Illinois, and Indiana south to southern Alabama and northwestern Florida (Decher and Choate 1995); occurs primarily in the cave region of Missouri, Arkansas, Kentucky, Tennessee, and Alabama. Summer and winter ranges are essentially the same.
Sources and Credits
- (c) U.S. Fish and Wildlife Service Headquarters, some rights reserved (CC BY), http://www.flickr.com/photos/50838842@N06/5687233983
- Adapted by rkkessler from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Myotis_grisescens
- (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31408423
- (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/26254093
- Adapted by rkkessler from a work by (c) Smithsonian Institution, some rights reserved (CC BY), http://eol.org/data_objects/16146915
- Adapted by rkkessler from a work by (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31408412
- Adapted by rkkessler from a work by (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/28816600
- Adapted by rkkessler from a work by (c) The Regents of the University of Michigan and its licensors, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/31408415
- Adapted by rkkessler from a work by (c) International Union for Conservation of Nature and Natural Resources, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/34587302
