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Montana Field Guide

Montana Field Guides

Pallid Bat - Antrozous pallidus

Species of Concern
Native Species

Global Rank: G4
State Rank: S3
(see State Rank Reason below)


Agency Status
USFWS:
USFS:
BLM: SENSITIVE
FWP SWAP: SGCN3



External Links





State Rank Reason (see State Rank above)
Species is uncommon within a limited area of southern Montana. No threats are identified but the species may be vulnerable to declines.
Pallid Bat (Antrozous pallidus) Conservation Status Summary
State Rank: S3
Review Date = 01/19/2024
How we calculate Conservation Status
Rarity: VeryUncommonVeryCommon Threats: HighlyThreatenedUnthreatened Trends: RapidlyDecliningDecliningStableIncreasing Rank: S1 S2 S3 S4 S5 CriticallyImperiledSecure

See the complete Conservation Status Report
 
General Description
The Pallid Bat is large and pale, with large ears (not joined at base), large eyes, a simple muzzle, and a yellowish drab dorsal pelage that is paler towards the hair tips and darker at the base (palest in deserts, darkest along coast). The calcar lacks a keel. The total length is 92 to 135 millimeters, tail length is 35 to 53 millimeters, hind foot length is 11 to 16 millimeters, ear length is 21 to 37 millimeters, forearm length is 45 to 60 millimeters, and skull length is 18.6 to 24 millimeters. Females tend to be larger than males (mass 13.6 to 24.1 grams in males, 13.9 to 28.0 grams in females) (Hermanson and O'Shea 1983). The skull has 28 teeth (dental formula: I 1/2, C 1/1, P 1/2, M 3/3) (Nagorsen and Brigham 1993).

Diagnostic Characteristics
The Pallid Bat differs from most other Vespertilionids found in Montana in having much larger ears, larger eyes, and paler pelage. The “pig-like” nostrils are also diagnostic. It differs from the Townsend's Big-eared Bat (Corynorhinus townsendii) by lacking the lumps on the nose, having ears that are not joined at the base, a pale rather than brownish pelage, and a larger body size. It differs from the Spotted Bat (Euderma maculatum) most noticeably by lacking the dark pelage with the prominent white spots. It is the only bat species found in Montana with two pair of lower incisors. Pallid Bats also have a distinctive skunky odor.

The species is readily identified in-hand, and both roost surveys and mist netting are effective survey tools for detection. Visual encounter surveys of rock outcrops where the observer looks under rocks and in cracks and crevices with a high-powered light have been effective as documenting this species, although detection rates are low. Mist-net captures at drinking sites have been the most effective survey technique. The species is typically captured at moderately sized reservoirs and ponds or smaller water sources that have adequate flyways to allow approach and departure of this large bat.

Detection using acoustic methods is possible. Three long-term detector stations have recorded Pallid Bat call sequences, but confidence in species identification is typically low and high volumes of calls are needed to determine presence.

Species Range
Montana Range Range Descriptions

All Ranges
Summer
Migratory
(Click legend blocks to view individual ranges)

Western Hemisphere Range

 


Range Comments
Although the core range of the Pallid Bat in Montana has been characterized, the species may be more broadly distributed than currently recognized. The species has been documented in xeric environments from the Pryor Mountains north to the Bull Mountains and east to the Ashland District of the Custer Gallatin National Forest. These areas are primarily Sagebrush Steppe intermixed with Ponderosa pine or Juniper forest with abundant rock outcrops.

Observations in Montana Natural Heritage Program Database
Number of Observations: 22

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density

Recency

 

(Observations spanning multiple months or years are excluded from time charts)



Migration
Whether Pallid Bats migrate to areas within or outside of Montana is currently unknown. The species has not been observed between October and April, but observations are sparse across space and time within Montana so whether this absence represents hibernation or migration is uncertain. Most records are from summer (Shryer and Flath 1980, Worthington 1991, P. Hendricks and J. Carlson personal observation). Little information is available outside of Montana (Barbour and Davis 1969, Schmidly 1991). Distances of fall movements are not known, but Pallid Bats seem to be somewhat sedentary and probably do not move far between summer and winter roosts (Barbour and Davis 1969).

Habitat
Habitat at the Carbon County sites is Utah juniper (Juniperus osteosperma) and black sagebrush (Artemisia nova). The Rosebud County site is in an area of ponderosa pine (Pinus ponderosa) and big sagebrush (Artemisia tridentata). Both areas have rock outcrops (limestone or sandstone) in the immediate vicinity or within short flying distance. This species has not yet been detected at caves or abandoned mines in Montana, but has been found using crevices in sandstone outcrops; most observations have been at water sources (spring-fed streams or ponds; e.g. Carbon County) (Shryer and Flath 1980). However, habitat use in Montana by this species remains poorly known and unstudied.

At other locations, Pallid Bats have been found in arid deserts, juniper woodlands, sagebrush shrub-steppe, and grasslands, often with rocky outcrops and water nearby. They are less abundant in evergreen and mixed conifer woodlands, but in British Columbia are found in ponderosa pine forest near cliffs (Nagorsen and Brigham 1993). They typically roost in rock crevices or buildings, less often in caves, tree hollows, under bridges, and in abandoned mines (Hermanson and O'Shea 1983, Verts and Carraway 1998); night roosts often are in caves in Oklahoma (Caire et al. 1989). Four summer roosts in Wyoming were in rock shelters (1), caves (2), and mines (1) (Priday and Luce 1997). Day and night roosts are usually distinct. In Oregon, night roosts were in buildings, under rock overhangs, and under bridges; Pallid Bats generally were faithful to particular night roosts both within and between years (Lewis 1994). Night roosts in British Columbia were often in cavities in ponderosa pine (Nagorsen and Brigham 1993). Day roosts include rock piles, tree hollows, and rock crevices. Pallid Bats found in caves or mines usually use crevices within these places (Hermanson and O'Shea 1983, Caire et al. 1989). Maternity colonies are often located in horizontal crevices in rock outcrops and man-made structures, where temperatures are a fairly constant 30 degrees.

Ecological Systems Associated with this Species
  •  Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: mtnhp.org/requests) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2012.  Mammals of Montana.  Second edition.  Mountain Press Publishing, Missoula, Montana.  429 pp.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Food Habits
The primary diet is arthropods, which are often captured on the ground after an aerial search. They also capture some food (large insects) in flight, within a few meters of ground vegetation. Food items include flightless arthropods, such as scorpions, solpugids, centipedes, Jerusalem crickets, grasshoppers, moths, and beetles; they may eat small vertebrates, such as lizards and mice (O'Shea and Vaughan 1977, Hermanson and O'Shea 1983, Johnston and Fenton 2001). Pallid Bats also visit bat-adapted plants (e.g., Agave), and may be seeking insects (Herrera et al. 1993). In the southern portions of its range it appears to be a facultative nectivore and readily forages on the nectar and fruit of cacti (Frick et al. 2009). Foraging often occurs at 0.5 to 2.5 meters above ground. The diet and foraging behavior in Montana have not been reported or studied.

Ecology
Pallid Bats are active in Arizona from early April through October; Oregon records extend from mid-April to late September (O'Shea and Vaughan 1977, Verts and Carraway 1998). Relative to other bat species, they emerge from roosts relatively late in the day (45 minutes or more after sunset), which may protect them from some aerial predators. They are a gregarious species. They usually form clusters in diurnal roosts, and may also gather in night roosts that are frequently near, but separate from, day roosts (Lewis 1994). Brazilian Free-tailed Bat (Tadarida brasiliensis) and Yuma Myotis (Myotis yumanensis) may roost among Pallid Bats in some regions (Hermanson and O'Shea 1983). Pallid Bats are pollinators of columnar cacti and agaves in the Sonoran and Chihuahuan deserts, although they may be visiting the flowers to capture insects (Herrera et al. 1993). There appear to be no estimates of abundance for any locality where this bat occurs. The ecology and predators in Montana have not been studied or reported.

Reproductive Characteristics
Capture of males, lactating females, and juveniles indicates reproduction is occurring in Montana (Worthington 1991, Foresman 2012), although timing of reproductive events is poorly defined. Lactating females have been captured in early August (P. Hendricks and J. Carlson personal observation), and juveniles in August and early September.

Based upon data gathered from other locations, copulation usually occurs in October to December. Maternity colonies are situated where temperatures are a fairly constant 30 degrees. Fertilization is delayed until spring. In the U.S., young are born in late May to early June in California, mostly late June in Kansas, and probably early May to mid-June in Texas (Schmidly 1991). The normal litter size is 2, but sometimes only one young is born. Young begin to fly at 6 weeks and are weaned in 6 to 8 weeks (Hermanson and O'Shea 1983). In Oregon, reproductive success was reduced in a year with low spring temperatures, and roost-site switching by pregnant and lactating females was correlated to ectoparasite loads (Lewis 1993, 1996). Maternity colonies usually are small, but may include up to 200 adults, including a few adult males (O'Shea and Vaughan 1977, Hermanson and O'Shea 1983, Lewis 1996).

Management
Pallid Bats have persisted for over 20 years in the general area of the state where they were first discovered (Shryer and Flath 1980, Worthington 1991, P. Hendricks and J. Carlson personal observation). This is encouraging, given that essentially nothing is known of abundance, reproductive biology, habitat requirements, movements, and roost site selection in Montana, nor have the potential threats to this bat been identified. The lack of information on this species makes development and implementation of any effective management activity tenuous at best. Fortunately, the roosting habitat often favored by this bat (crevices in cliffs and rock outcrops) provides it protection from many kinds of disturbance. Nevertheless, any roosts that are discovered should be protected and monitored, as Pallid Bats also use abandoned buildings and bridges as roosts. Studies to fill the gaps in our knowledge of this bat in Montana are needed, especially surveys throughout the state in appropriate habitats and landscapes to determine the full extent of its distribution. The most immediate management action that can benefit this species (and other bat species as well) is protection of water sources in arid regions where this bat is present and water sources are limited. Open waste sumps, and similar hazardous standing water bodies associated with oil and gas fields, could present a significant hazard to Pallid Bats and other bat species as these energy resources are exploited.

Pallid Bat is not managed in Montana. It is currently a Species of Conservation Concern, primarily due to limited information and perceived rarity. Pseudogymnoascus destructans (Pd) has not been detected on Pallid Bats nor have individuals been found with symptomatic White-Nose Syndrome (WNS, White-Nose Syndrome Response Team 2020). The species distribution is on the leading edge of the disease as it progresses westward, so it is difficult to say whether it is susceptible to WNS or carries Pd. Wind energy does not appear to be a concern for the species as mortalities have not yet been documented (AWII 2018).

Perhaps the most meaningful impacts managers can have on this species in Montana are through conservation of water in dry areas. Pallid bats are relatively large animals and require areas of open water with adequate flyways to drink. Managers should ensure water is present in large stock tanks and reservoirs throughout the spring, summer, and early fall and remove encroaching vegetation that may impede approach or departure from waterbodies.

Stewardship Responsibility

Based on the Montana Natural Heritage Program's latest predicted habitat suitability model

Total species' range in Montana 44,712 km2 (12% of Montana)
Area predicted to have
some level of suitable habitat
33,115 km2 (9% of Montana)

Stewardship responsibility for the predicted area of suitable habitat can be broken down as follows

  Total Suitable Optimal Suitability Moderate Suitability Low Suitability
Federal 11% <1% 6% 5%
State 4% <1% 1% 3%
Local <1% <1% <1%
Conservation Lands/Easements 1% <1% 1%
Private/Tribal/Unknown 83% <1% 22% 61%

See the Habitat Suitability for Biodiversity task in Map Viewer for a more detailed look at stewardship responsibilities within a variety of local jurisdictions.


References
  •  Literature Cited Above
  •  Additional References
  •  Web Search Engines for Articles on "Pallid Bat"
  •  Additional Sources of Information Related to "Mammals"
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Citation for data on this website:
Pallid Bat — Antrozous pallidus.  Montana Field Guide.  .  Retrieved on , from