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

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Western Yellow Bat

      (Lasiurus xanthinus)

Western Yellow BatWestern Yellow BatWestern Yellow Bat
  • DESCRIPTION
  • DISTRIBUTION
  • HABITAT
  • CONSERVATION
  • MULTIMEDIA

General Description

The western yellow bat (Lasiurus xanthinus) is a medium to large-sized bat, whose fur is yellowish-buff to light brownish, with fur tipped with gray or white. This species weighs an average of 0.32-0.8 oz (9.2 to 22.5 g), and wingspan ranges from 13-14 inches (33.5 to 35.5 cm). Ears are shorter than many other species, but their length is larger than their width. The anterior half of skin between the legs is well-furred, while the posterior half is bare or almost bare. Yellow bats are known to be sexually dimorphic in size, with females being slightly larger.

Legal Status

The western yellow bat is not federally listed as threatened or endangered. It is included in a draft list of Arizona Wildlife of Special Concern by the Arizona Game and Fish Department. According to the State of Nevada Comprehensive Wildlife Conservation Strategy, the western yellow bat is a Nevada Species of Conservation Priority. California Department of Fish and Wildlife have proposed it as a species of special concern. The International Union for Conservation of Nature lists the western yellow bat as least concern. The Western Bat Working Group lists the western yellow bat as a species of “Red or High” priority, the highest priority available.

Taxonomy

The western yellow bat was previously recognized as a subspecies of the southern yellow bat (Lasiurus ega xanthinus). They were separated into two distinct species between 1988 and 1995. Some continued to recognize L. e. xanthinus through 1995. The western yellow bat differs from the southern yellow bat by having a brighter yellow pelage, especially on the tail membrane; however, this characteristic is difficult to detect so it is best to distinguish the two by range.

Reproduction

Females usually give birth to two young in early June-July, and pregnant females have been found as early as late April. Breeding biology is not well understood. Breeding time is unknown; however, it is thought that females store sperm and both males and females probably can breed within their first year.

Diet

Western yellow bats feed on a variety of insects including ants, wasps, bees, flies, mosquitoes, butterflies, moths, beetles, grasshoppers, crickets, and others. They are known to leave day roosts and begin foraging at dusk. Yellow bats have been captured over water holes but it is unknown if they were foraging or drinking.

Threats

Known predators of the western yellow bat include domestic cats and dogs and barn owls. Predators of other foliage roosting bats include birds of prey, roadrunners, and opossums. Woodpeckers and raccoons have been observed disturbing other tree-roosting species at their roosting sites. The use of pesticide threatens both bats and their insect prey. The major threat to most bat species is the loss of habitat, including open water, which degrades roosting and foraging areas. The cosmetic trimming of palm trees is probably one of the primary threats to yellow bats. Human threats include barbwire fences and vehicles, as well as the negative image many have about bats.

More Information

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

Updated December 8, 2017

The first known occurrence of the western yellow bat in the United States was found in Palm Springs, California, in November 1945. No other individuals were observed in the United States until January and February 1960, when two yellow bats were found roosting in dead palm fronds while trees were being trimmed at the University of Arizona in Tucson. In 1963, yellow bats were captured in Guadalupe Canyon, New Mexico, along a riparian corridor. In 1966, it was published that yellow bats had been found in Scottsdale, Phoenix, and Yuma, Arizona. The yellow bat’s historic range appears to be southern New Mexico, west through central Arizona and southern California, and southward into central and western Mexico, including Baja California.

General range maps for the western yellow bat include the southern portion of California, the southern half of Arizona, and the southwestern corner of New Mexico. The range continues south into Baja, California, and west and central Mexico. The species has recently been found as far north as Moapa Valley in southern Nevada. Currently, it is believed that the western yellow bat has expanded its range across the southwestern United States northward with the introduction of the Washington fan palm. It has also been confirmed farther east, in Big Bend National Park in Texas.

The first known occurrence along the lower Colorado River (LCR) was in Yuma, Arizona, in 1963.  In Arizona, they are found at elevations from 550-6000 feet (168 to 1,830 meters). Western yellow bats have been detected along the LCR during acoustic and capture surveys.

Information about acoustic surveys and capturing bats can be found at the LCR MSCP Bats research and monitoring web page.

 

Western yellow bats prefer riparian woodland habitat, especially where palm trees are found nearby. A study (found here) along the LCR compared bat acoustic activity within four riparian habitat types: cottonwood-willow, mesquite, Tamarisk, and marsh. Of these four habitat types, western yellow bat occupancy was significantly higher in cottonwood-willow compared to the others. Western yellow bats are known to roost in the dead palm frond skirts of fan palms. In Guadalupe Canyon, New Mexico, broadleaf deciduous riparian trees, such as Fremont cottonwood, sycamore, and hackberry, were used as roosting sites. In the Big Bend region of Texas, a western yellow bat was found using the giant dagger yucca as a roosting site, in a similar manner as those using palm trees. Roosting height can range from 7.2 feet (2.2 m) from the ground to the tallest palm or deciduous trees in the area. Palm trees may be preferred because dead fronds closely match their fur coloration, although they will utilize any tree that gives them enough cover to be hidden while roosting. 

 

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 western yellow bat. Click on the arrows to expand the table.

WYBA1—Conduct surveys to determine species distribution of the western yellow bat

Conduct investigations to identify the distribution of the western yellow bat in Reaches 3–5.

WYBA2—Avoid removal of western yellow bat roosts trees

To the extent practicable, avoid removal of palm trees that could serve as roosts for the western yellow bat when creating covered species habitats.

WYBA3—Create 765 acres of western yellow bat roosting and foraging habitat

Of the 7,260 acres of cottonwood-willow and honey mesquite to be created as covered species habitat, at least 765 acres will be designed and created to provide western yellow bat roosting  or foraging habitat. Created roosting or foraging habitat will be designed and managed to support cottonwood-willow types I and II and honey mesquite type III. The LCR MSCP process for selecting sites to establish cottonwood-willow and honey mesquite as habitat for other covered species habitat will, based on the information collected under conservation measure WYBA1, give priority, when consistent with achieving LCR MSCP goals for other covered species, to selecting sites that are occupied by the western yellow bat 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 will provide roosting or foraging habitat and 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.

AMM1—To the extent practicable, avoid and minimize impacts of implementing the LCR MSCP on existing covered species habitats

To the extent practicable, establishment and management of LCR MSCP–created habitats will avoid removal of existing cottonwood-willow stands, honey mesquite bosques, marsh, and backwaters to avoid and minimize impacts on habitat they provide for covered species. Temporary disturbance of covered species habitats, however, may be associated with habitat creation and subsequent maintenance activities (e.g., controlled burning in marshes and removal of trees to maintain succession objectives). LCR MSCP conservation measures that could result in such temporary disturbances will, to the extent practicable, be designed and implemented to avoid or minimize the potential for disturbance. In addition to implementing AMM3 and AMM4 below, these measures could include conducting preconstruction surveys to determine if covered species are present and, if present, implementing habitat establishment and management activities during periods when the species would be least sensitive to those activities; or redesigning the activities to avoid the need to disturb sensitive habitat use areas; staging construction activities away from sensitive habitat use areas; and implementing BMPs to control erosion when implementing ground disturbing activities.

AMM5—Avoid impacts of operation, maintenance, and replacement of hydroelectric generation and transmission facilities on covered species in the LCR MSCP planning area

To the extent practicable, before implementing activities associated with OM&R of hydroelectric generation and transmission facilities, measures will be identified and implemented that are necessary to avoid take of covered species where such activities could otherwise result in take. These measures could include conducting surveys to determine if covered species are present and, if so, deferring the implementation of activities to avoid disturbance during the breeding season; redesigning the activities to avoid the need to disturb covered species habitat use areas; staging of equipment outside of covered species habitats; delineating the limits of vegetation control activities to ensure that only the vegetation that needs to be removed to maintain infrastructure is removed; stockpiling and disposing of removed vegetation in a manner that minimizes the risk of fire; and implementing BMPs to control erosion when implementing ground disturbing activities.

AMM6—Avoid or minimize impacts on covered species habitats during dredging, bank stabilization activities and other river management activities

To the extent practicable, before initiating activities involved with river maintenance projects, measures will be identified and implemented that avoid or minimize take of covered species where such activities could otherwise result in take. Such measures could include alternative methods to achieve project goals, timing of activities, pre-activity surveys, and minimizing the area of effect, including offsite direct and indirect effects (e.g., avoiding or minimizing the need to place dredge spoil and discharge lines in covered species habitats; placing dredge spoils in a manner that will not affect covered species habitats).


Research and Monitoring Activities

LCR MSCP conduct 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.

 

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

Yellow bat roosting in cottonwood after being released at the Colorado River Indian Tribes 'Ahakhav Tribal Preserve, July 2008  - Photo by Reclamation Yellow bat captured at the Colorado River Indian Tribes 'Ahakhav Tribal Preserve, July 2008 - Photo by Reclamation Yellow bat captured at the Colorado River Indian Tribes 'Ahakhav Tribal Preserve, September, 2007 - Photo by Reclamation