Family Vespertilionidae—The vespertilionids are the commonest bats in the U.S. and in our region. The most common genus is Myotis, often called mouse-eared bats. They tend to be rather nondescript creatures differing in such external features as overall size, size of ears, hairiness of the membranes, shininess of the pelage, and size of the feet. Prominent differences in the skull tend to evolve around size, slope of the forehead, and presence or absence of a sagittal crest.
Tending to specialize ecologically, some montane areas of central New Mexico may have five or six species commonly occurring together. Three species tend to specialize in feeding over water: M. yumanensis, M. lucifugus, and M. velifer. These species seldom are found distant from relatively large bodies of open water. Three other species tend to be hovering gleaners: M. evotis, M. auriculus, and M. thysanodes. Gleaners specialize in picking prey off of such things as leaves, tree trunks, rocks, or the ground. The remaining three species in our area are aerial pursuers: M. californicus, M. ciliolabrum, and M. volans). These species tend to patrol back and forth in open areas, capturing flying prey.
Members of the last group have a keeled calcar (and only members of this group within the region). M. volans tends to be a montane species, as does M. ciliolabrum (though less strictly); M. californicus tends to be a desert and grassland animal, mostly west of the Rio Grande and south of central New Mexico.
The gleaners all have relatively long ears (extending appreciably beyond the nose when laid forward). M. thysanodes tends to occur lower in elevations, being most common from woodland down. The other two species are very similar, with M. auriculus is most common in the mountains of west-central and southwestern New Mexico, while M. evotis is most common in the mountains of northern New Mexico within our region. However, both occur in several ranges in central and west-central New Mexico, where ear color usually will tell them apart (black in evotis, brown in auriculus).
The myotis associated with water all have relatively short ears. Myotis velifer is mostly southern in our region (roughly southern 1/3 of New Mexico; Trans-Pecos Texas); it tends toward dull, grayish pelage and the skull has a sagittal crest. Myotis yumanensis and M. lucifugus are very similar, but M. lucifugus tends to be most common at higher elevation, to have a more sloping forehead, and display burnished tips to the hairs of the pelage; M. yumanensis tends to be more common at lower elevations, has a more steeply sloping forehead, and lacks the burnished tips to its hairs.
The genus Euderma is represented by one species, E. maculatum, the Spotted Bat, which is perhaps the most striking bat north of the Mexican border, with huge ears, three white spots on the back, and a more or less sepia ground color on the dorsum. Although named in 1891, none was captured in nature by a scientist until 1960; they are listed as rare on the list of "Rare and Endangered Species." They now have been taken or observed from British Columbia to Durango (Mexico), but little is known of their natural history. They appear to be a crevice dweller amongst rocks and to feed extensively on moths, but also have been observed capturing prey on the ground.
Idionycteris phyllotis has been considered by some to belong in the genus Euderma. It also has been placed in Plecotus. Its range runs from central Mexico northwesterly to southeastern Utah and southern Nevada.
Corynorhinus townsendii (Townsend's Big-eared Bat) is closely related to the two species just treated (and, in fact, this species and Allen's Big-eared Bat have been placed together in the genus Plecotus in relatively recent time; Plecotus now is retained only for Old World species of the group). This bat is much more common than Euderma, being widely spread through western North America with scattered populations from Oklahoma to Virginia. It is quite common locally. It hibernates in the region and is the only bat regularly found hibernating here. It usually is found in caves and mines.
Townsend's Big-eared Bat images.
The Pallid Bat (Antrozous pallidus) is one of the most common local bats and often is seen cruising street lights after insects attracted by the lights. It may be the most desert-adapted of our local bats and occurs most often in desert and grasslands, though it may be taken rarely as high as lower Ponderosa Pine forest. In captivity, it has gone as long as a month without the intake of free water. It tends to be a crevice dweller, though it also may be found in caves and buildings. It often will take terrestrial invertebrates and small vertebrates from the ground.
The Big Brown Bat (Eptesicus fuscus) is most common in forested, higher elevations in our region, but good-sized colonies have been found in El Paso (Fort Bliss). It is one of the most widespread of the bats that occur locally, extending throughout North America from nearly tree line in the north and continuing into South America. It occur regularly in fossil Pleistocene faunas from caves in the Southwest, where, in common with a number of other animals, individuals are larger than the local individuals today.
The Western Pipistrelle (Pipistrellus hesperus) also is a common bat in our area, but limited fairly strictly to the vicinity of rocky areas and probably only those rocky areas that have a source of water fairly close by. It spends the day in crevices or even under rocks. Activity starts quite early in the evening, when there still is sufficient light to see them clearly. It is a small bat whose black mask and membranes usually contrast strongly with the light body pelage. It occurs through most of the Southwest and north to Washington and south well into Mexico.
Lasionycteris noctivagans (Silver-haired Bat) is another widespread species, occurring almost throughout the U.S. and southern Canada, but barely into Mexico. Although often considered to be tree bats, they most often have been found roosting in fissures (beneath bark, rock crevices) or in buildings or natural openings. In our region, they are most common in June, when most individuals caught are males; the small numbers of females caught in fall have already been inseminated. In summer, the higher mountains are occupied; during spring and fall migrations, they may be found almost anywhere. There are no winter records for the region.
The genus Lasiurus includes several species of tree bats. The most widespread is the Hoary Bat (Lasiurus cinereus) which migrates through the area; males remain during the summer in the high mountains, but the females move on (probably to the eastern U.S.) to give birth. The animal is well adapted for roosting in the open, with more fur (and fur with better insulating qualities than found in most bats) and with the ability to withstand cold temperatures and water loss. The Yellow Bat (L. ega) is primarily a tropical and subtropical bat, entering the U.S. only at the southern tip of Texas and southern California, southern Arizona, and the bootheel of New Mexico; its range continues south into South America. Apparently two species of red bats overlap in the south-central portion of the region. The Red Bat (Lasiurus borealis) is an eastern species reaching the El Paso region from the east and L. bossevillii is a western species reaching the area from the west. Although the Great Plains from southern Canada east to the East Coast is inhabited by Red Bats, they are relatively rare in our region. There are records from the Lower Valley of El Paso, from near Las Cruces, and from Carlsbad Caverns.
Last Update: 23 Jan 2008
Centennial Museum and Department of Biological Sciences, The University of Texas at El Paso