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Lower Colorado River Multi-Species Conservation Program Balancing Resource Use and Conservation

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Townsend's Big-Eared Bat

      (Corynorhinus townsendii)

Townsend's Big-Eared BatTownsend's Big-Eared BatTownsend's Big-Eared Bat
  • DESCRIPTION
  • DISTRIBUTION
  • HABITAT
  • CONSERVATION
  • MULTIMEDIA

General Description

The Townsend’s big-eared bat (Corynorhinus townsendii) is a medium-sized bat with a wingspan of 11.8-13.4 inches (30-34 cm), and a weight of 0.28 to 0.5 oz (8-14 g). Fur ranges from slate gray to pale with cinnamon brown to blackish brown tips. Ears are very large (1.2-1.9 inches or 30-39 mm) and are joined across the forehead. The most significant characteristics are two large glandular lumps on each side of the nose, which help distinguish it from the four other large-eared bat species that may be found along the LCR: the spotted bat, the California leaf-nosed bat, the Allen’s big-eared bat, and the Pallid bat.

Legal Status

Two eastern subspecies of Townsend’s big-eared bat have been listed by the U.S. Fish and Wildlife Service as endangered under the Endangered Species Act. The Bureau of Land Management, in California, has placed Townsend’s big-eared bat on their animal sensitive species list. State designations include mammalian species of special concern in California and a species of conservation priority by Nevada Department of Wildlife. The Western Bat Working Group lists it as a species of “Red or High” priority, the highest priority the group gives. The International Union for Conservation of Nature (IUCN) red list of threatened species lists the species as vulnerable, it’s third-highest rating.

Taxonomy

The name for the Townsend’s big-eared bat (Corynorhinus townsendii) has changed often since it was first described.  Both the genera and species name has undergone many changes. Currently there are 5 recognized subspecies of C. townsendii in the United States, 2 (C. t. townsendii and C. t. pallescens) in the western U.S., and 2 (C. t. ingens and C. t. virginianus) in the eastern U.S., and 1 (C. t. australis) with a primarily Mexican distribution, that overlaps with C. t. pallescens in western Texas.

Reproduction

Breeding occurs in the hibernacula from October to February, although some individuals may mate prior to arriving. Males will perform a courtship ritual. Females may breed as early as 4 months of age. Males are not reproductively active until their second year. Females may mate with several males during the winter, and will store sperm until the spring when ovulation and fertilization occur. Maternity colonies form from March through April or later, depending on the elevation, and can range in size from 12 to 200 females in the western United States. Roost temperature appears to be a factor in site selection for maternity colonies. Between May and July a single young is born, and fully weaned at 6 weeks.

Diet

Townsend’s big-eared bats are considered moth specialists. Other insects found to be preyed upon include beetles, flies, bees, and wasps. Generally, they take their prey in the air, although evidence of foliage gleaning has been noted. There have been two peaks of foraging activity observed, one right after leaving the roost, and a second that occurs close to sunrise the following morning. Females in a maternity roost were recorded having three feeding periods throughout the night; they return to the roost after each feeding. As offspring matured, females decrease how often they returned to the roost; once the young mature, the females do not return until sunrise. Night or feeding roosts are also used by big-eared bats. Night roosts are usually found much closer to feeding areas because these roosts main use is for a place to feed on large prey items that cannot be eaten in mid-flight. Feeding roosts of most species are identified by a culmination of insect body parts (mainly moth wings for Townsend’s big-eared bats) on the floor of the roost.

Threats

Predation is a threat to most bats, including Townsend’s big-eared bats. Specific predators of Townsend’s big-eared bats include black rat snakes, spotted skunks, house cats, ringtails, rats, domestic cats, dogs, birds of prey, snakes, raccoons, weasels, predatory song birds, frogs, large spiders, and even other bats. Bats, in general, are preyed upon by a number of different animals, although most of these are not bat specialists and bats are usually a rare occurrence in their total diet. While humans are not predators of bats, the negative image many have about bats may be a serious threat.

Human-caused disturbances occur in a variety of different ways. The loss of roosting habitat for this sedentary species may be one of the most serious threats to not only Townsend’s big-eared bats, but other species as well. Townsend’s big-eared bats lose roosting habitat by either the destruction of the roost or by abandonment after a disturbance. Disturbance to maternity roosting sites has been found to be a serious danger to Townsend’s big-eared bat populations. Disturbance to hibernacula may also be a danger because it causes an increase in activity, which may cause bats to expend too much energy, causing them to starve to death.

More Information

Additional information on this species, as well as source documentation, can be found in the species accounts located at this link (PDF). Technical Reports on this species can be found here.

Updated November 26, 2012

Historically, the western subspecies of Townsend’s big-eared bat had a wide distribution, and originally were separated by morphologic characters.  One range of one subspecies included the western portions of California, Oregon, Washington, and British Columbia. The range of another included the eastern portions of those Pacific coast states and the province, as well as all of Idaho, Nevada, Arizona, New Mexico, Utah, and Wyoming, more than half of Montana, most of Colorado, western South Dakota, part of the Great Plains, and northwestern Mexico (not including the Baja Peninsula).

Click on the map below to see the distribution range of the Townsend's big-eared bat using the interactive GIS map.

Click here to see the distribution range of the Townsend's Big-eared bat

The current range of the species continues to include all areas where Townsend’s big-eared bats were historically found, although there have been major population declines in many areas, including the loss of many historic roosting sites along the LCR. 

The only current site to have a known colony (less than 50 in 2003) along the LCR is a mine located in the Riverside Mountains. There are two known roosting sites inside the Lake Mead National Recreation Area (NRA). Townsend’s big-eared bats have been recorded acoustically from March through October at Las Vegas Wash, which empties runoff from the Las Vegas Valley into Lake Mead. There may be a population in the area, although no roosts are known at this time. Two maternity roosts were found along the Bill Williams River, a major tributary that empties into Lake Havasu, north of Parker, Arizona. Townsend’s big-eared bats have also been observed in Moapa Valley, Nevada, near the Muddy River, which empties into the Overton Arm of Lake Mead.

 

Foraging habitat varies widely between area and subspecies. One subspecies was found to forage more in open fields, pastures, and cliffs, rather than in nearby forested areas, while another was found to use edge habitat or habitat in close proximity to vertical structures such as trees and cliffs more often than open field or woodland habitat. One telemetry study found that Townsend’s big-eared bats concentrated foraging activity along the edges of riparian vegetation and generally were found in the vicinity of vegetation when traveling to foraging areas from the roost sites. There appears to be an association between foraging sites and the location of mines and caves that big-eared bats use as roosts.

Townsend’s big-eared bat is primarily a cave-dwelling species that also roosts in old mines. This bat does not generally associate with other species in its roosts, particularly at maternity and hibernating sites. Unlike maternity colonies, bachelor (and non-reproductive female) roosting sites usually contain one to several individuals. Along the LCR, males may be territorial and roost alone unless the site is very large. Bachelor roost selection is not as complex as it is for maternity colonies.

 

LCR MSCP Conservation Measures

The Habitat Conservation Plan provides conservation measures specific to each species. Listed below are the species specific conservation measures for the Townsend big-eared bat. Click on the arrows to expand the table.

PTBB1—Conduct surveys to locate pale Townsend's big-eared bat roost sites

Conduct investigations to identify locations of pale Townsend's big-eared bat roost sites within 10 miles of the LCR MSCP planning area in Reaches 3–5.
PTBB2—Create covered species habitat near pale Townsend's big-eared bat roost sites

The LCR MSCP process for selecting sites to establish cottonwood-willow and honey mesquite as habitat for other covered species will, based on the information collected under conservation measure PTBB1, give priority, when consistent with achieving LCR MSCP goals for other covered species, to selecting sites that are within 10 miles of pale Townsend's big-eared bat roosts in Reaches 3–5. As described in Section 5.4.3 in the HCP, created cottonwood-willow and honey mesquite land cover will be designed to establish stands that will support a substantially greater density and diversity of plant species that are likely to support a greater abundance of insect prey species than is currently produced in the affected land cover types.
MRM1—Conduct surveys and research to better identify covered and evaluation species habitat requirements

Conduct surveys and research, as appropriate, to collect information necessary to better define the species habitat requirements and to design and manage fully functioning created covered and evaluation species habitats. This conservation measure applies to those species for which comparable measures are not subsumed under species-specific conservation measures (Section 5.7 in the HCP). They are not applicable to species for which habitat would not be created under the LCR MSCP Conservation Plan, such as the desert tortoise, relict leopard frog, humpback chub, and threecorner milkvetch.
MRM2—Monitor and adaptively manage created covered and evaluation species habitats

Created species habitats will be managed to maintain their functions as species habitat over the term of the LCR MSCP. Created habitat will be monitored and adaptively managed over time to determine the types and frequency of management activities that may be required to maintain created cottonwood-willow, honey mesquite, marsh, and backwater land cover as habitat for covered species. This conservation measure applies to those species for which comparable measures are not subsumed under species-specific conservation measures (Section 5.7 in the HCP). They are not applicable to species for which habitat would not be created under the LCR MSCP Conservation Plan, such as the desert tortoise, relict leopard frog, humpback chub, and threecorner milkvetch.
CMM1—Reduce risk of loss of created habitat to wildfire

Management of LCR MSCP conservation areas will include contributing to and integrating with local, state, and Federal agency fire management plans. Conservation areas will be designed to contain wildfire and facilitate rapid response to suppress fires (e.g., fire management plans will be an element of each conservation area management plan).
CMM2—Replace created habitat affected by wildfire

In the event of created-habitat degradation or loss as a result of wildfire, land management and habitat creation measures to support the reestablishment of native vegetation will be identified and implemented.

Research and Monitoring Activities

The LCR MSCP conducts a variety of research and monitoring activities along the LCR encompassing both MSCP and non-MSCP species. For a complete list of all activities, please see the Research and Monitoring Activities web page.

The following list includes different research and monitoring activities for bats. Click on the link for more information.

 

This gallery includes photos of this species. If you require larger photos, please contact our webmaster Michelle Reilly at mreilly@usbr.gov.