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

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California Leaf-Nosed Bat

      (Macrotus californicus)

California Leaf Nosed Bat - ReclamationCalifornia Leaf Nosed BatCalifornia Leaf Nosed Bat
  • DESCRIPTION
  • DISTRIBUTION
  • HABITAT
  • CONSERVATION
  • MULTIMEDIA

General Description

The California leaf-nosed bat (Macrotus californicus) is a gray-furred, medium-sized bat, which has a leaf-shaped structure on its nose. The ears are large (1.1-1.5 inches, 29-38 mm) and are joined near their base. Roosting leaf-nosed bats do not cluster in tight packs, as most other bat species. Total lifespan of California leaf-nosed bats is not known; however, one was recaptured after 15 years. California leaf-nosed bats do not migrate long distances nor do they hibernate. Instead they maintain a year-round presence by roosting in a cave or mine that maintains a high temperature (greater than 82ºF or 28ºC); many of these caves are geothermally heated.

Legal Status

The California leaf-nosed bat is not federally listed as threatened or endangered. The Bureau of Land Management (BLM) lists it as a sensitive species in Arizona, California, and Nevada. The State of California recognizes it as a mammalian species of special concern. This bat is listed as vulnerable by the Arizona Game and Fish Department and the California Department of Fish and Wildlife. The California leaf-nosed bat is a protected Nevada Species of Conservation Priority and is considered sensitive. The Western Bat Working Group lists the California leaf-nosed bat as a species of high priority. The International Union for Conservation of Nature (IUCN) red list of threatened species lists it as least concern.

Taxonomy

California leaf-nosed bats originally were classified as their own species. Later, they were classified as a subspecies (Macrotus waterhousii californicus) of a species of leaf-nosed bat found in Mexico, Guatemala, and the Caribbean. It regained species status in 1974 when it was found that M. waterhousii had a chromosomal diploid number of 2N = 46, while M. californicus had a chromosomal diploid number of 2N = 40. The shape of the skull was also found to be different, and where range overlap occurred, there was no evidence of hybridization. A renal (kidney) morphology study found that M. californicus can utilize drier habitat than M. waterhousii because of their greater ability to concentrate urine and conserve water. The narrow range overlap between these two species appears to be limited by habitat preference. California leaf-nosed bats are part of the neotropical family Phyllostomidae, which includes vampire bats and nectar feeding bats.

Reproduction

Females gather into maternity colonies in the spring and summer. These colonies usually range in size from 100 to 200 bats. Maternity colonies are either found in a different section of a mine/cave that is also used as a wintering site or one that is nearby. Males will roost separately but nearby to the maternity roost. Breeding takes place in the fall when males attract females with a courtship display that consists of wing-flapping and vocalizations. Males become territorial during these activities. After fertilization takes place, development of the embryo is delayed until the following spring. A single young is born between mid-May and early July. The species exhibits a high degree of philopatry, with females more strongly philopatric than males.

Diet

Echolocation and visual detection are used to locate prey, the latter being more highly developed than in other insectivorous bats. Leaf-nosed bats feed by capturing prey during flight and by gleaning insects from vegetation. They primarily feed on large night-flying beetles, grasshoppers, moths, and insect larvae, which they carry to a night roost to eat. These night roosts usually consist of shallow caves and short mining prospects that can be located by the accumulation of insect parts, such as wings, which are not eaten. Fruit-eating has also been reported, and a California leaf-nosed bat at Havasu National Wildlife Refuge was found feeding on a tree lizard. Foraging normally takes place during the first 3 hours after sunset, as well as the last 2 hours before sunrise. An individual bat may forage for nearly 2 hours in a given night.

Threats

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. Known bat predators include domestic cats, dogs, birds of prey, snakes, raccoons, weasels, predatory song birds, frogs, large spiders, and even other bats. While humans are not predators of leaf-nosed bats, the negative image many have about bats may be a serious threat.

Disturbance and closure of roost mines are the greatest threats to the California leaf-nosed bat. Disturbance may cause abandonment of roosts. The best way to keep a mine open for bats and safe for humans is to place a gate inside any and all entrances. Bat gates allow bats and other wildlife to freely enter and exit a mine while restricting the access of humans. Because the bats are restricted to specific roost requirements (such as temperature), their limited distribution causes them to form a small number of large colonies rather than several small ones. The loss of one colony can have a significant effect on the total population along the LCR.

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 December 8, 2017

The historical range of the California leaf-nosed bat included records from San Diego County and Riverside County, California, eastward to Tombstone, Arizona, and south into Baja California and Sonora, Mexico, with the center of its distribution appearing to be near the location of its first recorded description at Fort Yuma, California, opposite Yuma, Arizona. In 1937, leaf-nosed bats were found at a winter night roost east of Searchlight, Nevada, and in 1964 a large roost was found in a mine 4.5 miles north of Davis Dam and 0.75 miles west of Lake Mohave. At least three mines that were known roost sites were inundated by water with the formation of Lake Mead and Lake Mohave. Later the species was found along the Colorado River at the extreme northwest corner of Arizona, as well as farther east to Glenbar, Graham County, Arizona.

The current range includes southern Nevada, northwestern, central, and southwestern Arizona, and southwestern Chihuahua and Sinaloa, Mexico. Extensive surveys indicate that the California leaf-nosed bat's range in California is now limited to only the eastern portion of the state, although a bat survey in southwest San Diego County did record it at two different sites. All records in Arizona were from below 4,000 feet (1,220 m) in elevation, with most below 2,500 feet (7,625 m).

The California leaf-nosed bat has known populations all along the lower Colorado River, throughout reaches 1-6. There are 10 known maternity colonies found along the LCR with 7 of these considered major (more than 100 bats). There are also eight large winter roosts known of California leaf-nosed bats along the LCR. In addition to known colonies and roosts, California leaf-nosed bats have been detected along the LCR during acoustic and capture surveys.

Information about acoustic surveys of bats can be found at the LCR MSCP Bats Research and Monitoring web page. Information about capturing bats can be found at the LCR MSCP Bats Research and Monitoring web page.

Foraging usually takes place in dry desert washes, 3-6 miles from the roost. In the winter, this distance decreases to around one-half mile from the roost. Desert wash plant communities include: ironwood, palo verde, mesquite, catclaw, and smoketree. Evidence has also been found that leaf-nosed bats were utilizing riparian areas as well. During a study along the Muddy River in Moapa, NV, California leaf-nosed bats were detected acoustically in four distinct habitat types: riparian marsh, mesquite bosques, riparian woodlands, and riparian shrublands. Woodlands consisted of Fremont cottonwood, velvet ash, Goodding's willow, and Washington fan palms. Shrublands included stands of arrowweed and quailbush. Desert scrub habitat of the Sonoran and Mojave Deserts is dominated by creosote and bursage.

Roosting habitat is dependent on mines and caves that maintain high temperatures year-round. Because California leaf-nosed bats forage during the entire year, foraging habitat in close proximity to roosting sites may be more important during the winter months. Night roosts consist of shallow caves in natural situations, as well as manmade structures, including mining prospects, bridges, and buildings, which are also readily used near foraging habitat. The combination of day roosts, night roosts, and foraging habitat appears to be an important three-way association to support a population of California leaf-nosed bats.

 

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 California leaf-nosed bat. Click on the arrows to expand the table.

CLNB1—Conduct surveys to locate California leaf-nosed bat roost sites

Conduct investigations to identify locations of California leaf-nosed bat roost sites within 5 miles of the LCR MSCP planning area in Reaches 3–5.

CLNB2—Create covered species habitat near California leaf-nosed 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 CLNB1, give priority, when consistent with achieving LCR MSCP goals for other covered species, to selecting sites that are within 5 miles of California leaf-nosed 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.

 

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

California leaf-nosed bat captured at Cibola National Wildlife Refuge, October 2007 - Photo by Reclamation California leaf-nosed bat being released after capture at the Colorado River Indian Tribes 'Ahakhav Tribal Preserve, June 2011 - Photo by Reclamation California leaf-nosed bat caught in mist-net at the Colorado River Indian Tribes 'Ahakhav Tribal Preserve, June 2011 - Photo by Reclamation California leaf-nosed bat in hand, captured at the Colorado River Indian Tribes 'Ahakhav Tribal Preserve, August 2008 - Photo by Reclamation