Montana Field Guide

Spotted Bat - Euderma maculatum

Spotted bats have huge pink ears (37 to 50 millimeters long), the dorsum is blackish with a large white spot on each shoulder and on the rump, and white patches at the posterior base of each ear. Total length is 107 to 115 millimeters, forearm length is 48 to 51 millimeters, and weight is 16 to 20 grams. The greatest length of the skull is 18.4 to 19.0 millimeters (small sample). The supraorbital region of the skull is sharply ridged, but a median sagittal crest is absent; 34 teeth are present (Watkins 1977). The newborn young lack any indication of having the adult color pattern (van Zyll de Jong 1985). Four hours after birth, a male weighed 4 grams and measured 59 millimeters in length; tail length was 20 millimeters, hind foot 11 millimeters, ear 12 millimeters, and forearm 21 millimeters.

Spotted bats differ from other bats in Montana by the unique patterning of the fur and the extremely large ears. Their echolocation calls (an insect-like clicking) are audible to the unaided human ear.

Montana Range

Little information is available. The species has not been reported during winter in Montana.

Possibly some spotted bats migrate south for the winter, but there is no direct evidence of migratory movements. At least for lower elevation locations, spotted bats appear not to migrate (WESTECH Services 1981). Possibly they occupy coniferous stands in summer and migrate to lower elevations in late summer/early fall (Barbour and Davis 1969, Berna 1990). There are no winter records for British Columbia (Nagorsen and Brigham 1993), but mid- or late October records from here as well as Wyoming (Priday and Luce 1999) suggest that some individuals may over-winter without making an extensive migratory movement.

Spotted bats have been encountered or detected most often in open arid habitats dominated by Utah juniper (Juniperus osteosperma) and sagebrush (Artemisia tridentata and A. nova), sometimes intermixed with limber pine or Douglas-fir, or in grassy meadows in ponderosa pine savannah (Fenton et al. 1987, Worthington 1991b, Hendricks and Carlson 2001). Cliffs, rocky outcrops, and water are other attributes of sites where spotted bats have been found (Foresman 2001), typical for the global range. Spotted bat has been captured foraging over an isolated pond within a few kilometers of huge limestone escarpments in the Big Horn Canyon National Recreation Area, Carbon County (Worthington 1991a, 1991b), and the first record for the state was of an individual that flew in an open window at a private residence in Billings, Yellowstone County (Nicholson 1950). Roost habitats and sites have not been documented in Montana.

In other areas, spotted bats have been detected at water sources and in meadow openings, often with large cliffs nearby (Leonard and Fenton 1983, Storz 1995, Perry et al. 1997, Rabe et al. 1998, Gitzen et al. 2001).

Spotted bats roost in caves, and in cracks and crevices in cliffs and canyons, with which this species is consistently associated; it can crawl with ease on both horizontal and vertical surfaces (Snow 1974, van Zyll de Jong 1985). In British Columbia, individuals used the same roost each night during May through July, but not after early August (Wai-Ping and Fenton 1989). Winter habitat is poorly documented. A possible explanation for the early paucity of collections in natural situations is the bat's narrow habitat tolerance (Handley 1959, Snow 1974).

This species is insectivorous. Apparently spotted bats feed primarily on noctuid moths, and sometimes beetles (Barbour and Davis 1969, Schmidly 1991, van Zyll de Jong 1985). In Texas, the contents of 15 stomachs combined were 97.1% moths by volume, 2.7% beetles (Scarabidae), and 0.2% other insects (Easterla and Whitaker 1972); volumes in two of the stomachs were 10% and 30% beetles. In British Columbia, foraging took place 5 to 15 meters above ground (Wai-Ping and Fenton 1989). In southeastern Utah, spotted bats fed on small insects within 2 meters of the ground. Sometimes insects are captured on the ground (Poche and Bailie 1974), though this has been disputed. In Colorado, individuals foraged at heights above 10 meters (Navo et al. 1992). Timing and routes of foraging may sometimes be quite predictable and consistent (Leonard and Fenton 1983, van Zyll de Jong 1985, Wai-Ping and Fenton 1989, Rabe et al. 1998). Food habits and foraging ecology in Montana have not been reported or studied.

The spotted bat hunts alone, and at least sometimes appears to maintain exclusive foraging areas (Leonard and Fenton 1983), although in other cases individual foraging areas overlap (Wai-Ping and Fenton 1989). Neighboring bats show evidence of mutual avoidance and have been observed to turn away when encountering one another near the boundaries of their hunting areas.

The spotted bat has been reported active from early April to late October in British Columbia (Nagorsen and Brigham 1993), early June to mid-October in Wyoming (Priday and Luce 1999), and late March to late October in Nevada (Geluso 2000). The full extent of the active period in Montana is not known; records extend from late June to early August (Nicholson 1950, Worthington 1991b, Hendricks and Carlson 2001, Hendricks and Carlson personal observation).

Apparently spotted bats are relatively solitary but may hibernate in small clusters (Easterla 1973); roosts and hibernacula are usually located in cliffs, and to some degree caves. Individuals in British Columbia roost solitarily during the active season (Leonard and Fenton 1983). Home ranges may be relatively large. Foraging 6 to 10 kilometers from the day roost each night was documented in British Columbia (Wai-Ping and Fenton 1989); a lactating female in northern Arizona moved 38.5 kilometers between the day and night roosts, and a male flew 32 kilometers to a day roost (Rabe et al. 1998).

The echolocation call is loud and high-pitched; the fundamental frequency sweeps from 12 to 6 kHz and is a double or single steep frequency modulated pulse. The call is repeated at a rate of 2 to 6 per second and can clearly be heard by the unaided human ear at distances up to 250 meters (van Zyll de Jong 1985), a very useful feature for determining the presence of these bats during inventory work.

Normal predators have not been reported, but recently released individuals in early morning have been attacked by American Kestrel, Peregrine Falcon, and Red-tailed Hawk (Easterla 1973, Watkins 1977). Sources of mortality in Montana, other than human collection, have not been reported or studied.

Little information is available on spotted bat reproduction. A lactating female and a juvenile female were captured in mid-July 1990 at the same pond in Carbon County (Worthington 1991b).

In the southwestern states, young are born in late May or early June (Easterla 1973, Watkins 1977); time of birth in the north may be somewhat later (van Zyll de Jong 1985). A female in southwestern Texas gave birth to a single young on June 11 (Easterla 1973). A pregnant bat was collected in British Columbia on June 16. Lactating females have been captured from late June to early July in New Mexico (Findley and Jones 1965, Perry et al. 1997), from mid- to late July in Nevada (Geluso 2000), and mid-August in Utah (Barbour and Davis 1969). Post-lactating females were captured on August 28 and 29 in extreme northern Wyoming (Priday and Luce 1999). All evidence points to the birth of a single young (Easterla 1973, Watkins 1977), which remains with the mother the first few days even during flight. In Texas, testis size was greatest (10 x 3 millimeters, 11 x 3 millimeters) from late June through mid-July (Easterla 1973). Mating may take place in late summer in the south, and later in the north (Nagorsen and Brigham 1993), but reproductive data from across the range are limited.

Typical population age structure and longevity are unknown, but recruitment is expected to be low, given the low birth rate. Age at maturity is also not known, but females probably give birth in their second year.

Spotted bats have persisted for over 50 years in the general area of the state where they were first discovered (Nicholson 1950, Hendricks and Carlson 2001). 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. Fortunately, the roosting habitat most favored by this bat (cliffs) provides it protection from many kinds of disturbance. Nevertheless, any roosts that are discovered should be protected and monitored. Studies to fill the gaps in our knowledge about 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 audible calls make a survey much easier to conduct (Pierson and Rainey 1998), as no special skill is needed, other than familiarity with the calls and knowledge of the habitats likely to support spotted bats. 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 spotted bats and other bat species as these energy resources are exploited.