Montana Field Guide

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).

The pallid bat differs from most other vespertilionids in having much larger ears, larger eyes, and paler pelage. 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.

No information is documented for Montana; all records are from summer (Shryer and Flath 1980, Worthington 1991, P. Hendricks and J. Carlson personal observation).
Little information is available from other locations either (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 at the Carbon County sites is Utah juniper-black sagebrush (Juniperus osteosperma-Artemisia nova). The Rosebud County site is in an area of ponderosa pine (Pinus ponderosa) savannah 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 rock crevices, caves or abandoned mines in Montana; most observations have been at water sources (spring-fed streams or ponds; e.g. Carbon County) (Shryer 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 crevice 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; 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.

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), probably seeking insects (Herrera et al. 1993). 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.

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 is 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.

Capture of males, lactating females, and juveniles indicates reproduction is occurring in Montana (Worthington 1991, Foresman 2001), 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).

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.