Neotoma cinerea (Bushy-tailed Woodrat) probably is the most attractive of a generally attractive genus, with its large eyes and ears and with a heavily furred tail (and thus the name). It is limited geographically in our region to higher montane elevations in the northern part of New Mexico and to cliff areas in San Juan County (northwestern New Mexico) down into pinyon-juniper woodland. Farther north, it descends into the Big Sagebrush flats and, over much of its range, is the only Woodrat. It occurs north into North Dakota and northwest to the Northwest Coast and then to the Yukon and Northwest Territories of Canada.
Interestingly, this, along with the White-throated Woodrat, was the most common late Pleistocene species in southern New Mexico, being virtually ubiquitous. It has been suggested that a population may have lingered on into the Holocene in the Guadalupe Mountains of Texas, with an archaeological excavation of Pratt Cave (elevation 1590 m) having produced fossils of this species; the only dates available range from 1420 to 2320 radiocarbon years BP (Lundelius 1979). Other Holocene sites in the general area have not produced this species and there is a distinct possibility that Pleistocene remains are mixed in with the archaeological fauna.
Neotoma mexicana (Mexican Woodrat) occurs from Colorado near the Wyoming line to far southern Mexico. In the Southwest, it's primarily an animal of forested montane habitats, but may occur in lower elevations under special conditions. It occurs, for example, in the Carrizozo lava beds and in boulder fields at Elephant Butte, both at lower elevations than common for the taxon. At any elevation it usually is associated with rocks. Low-elevation occurrences in the Early Holocene (when summer temperatures may still have been somewhat cooler than today) such as the Khulo Site in south-central New Mexico suggest that possibly summer temperatures are limiting, with present-day pooling of cool air in deep fissures and rock piles allowing survival under special circumstances. Such cool-air effects in lava fields can be seen in the ice caves near Grants, NM.
Some paleontological evidence suggests that N. mexicana was absent from east of the Rio Grande in New Mexico until the end of the Pleistocene. The extensive Dry Cave fauna (Eddy County, NM) and Pendejo Cave (Otero County, NM) faunas lack the taxon until the Holocene, and it also appears in the Holocene in Big Manhole Cave near Carlsbad Caverns in Eddy County, NM. Under this scenario, N. mexicana entered New Mexico during the later part of the late Pleistocene from the southwest or west but was blocked from moving directly east. Spreading northward, it passed over the Rio Grande Valley in northern New Mexico or southern Colorado and only then was able to move into the highlands east of the valley.
Neotoma micropus (Southern Plains Woodrat) is mostly a Great Plains grassland animal, and thus is common in eastern New Mexico. It is found in grassland over approximately the southeastern two-thirds of New Mexico and almost reaches the Arizona border in southwestern New Mexico. It occurs pretty much throughout the Southern Plains from southwestern Kansas south into Mexico as far as San Luis Potosí. Where this rat occurs with N. albigula, the latter tends to be restricted more to rocky situations.
Neotoma stephensi (Stephen's Woodrat) is strongly associated with junipers (Juniperus spp.). It has a relatively restricted range, running from north of the Deming Plains in southwestern New Mexico north to the Four Corners area and west across Arizona to near the California/Nevada border. The association with junipers is so strong that nests normally can be identified solely on the basis of the large amount of juniper included. Middens may be built in rock crevices, about the base of junipers, and even, occasionally, as an arboreal nest in a juniper.
Several genera of mice having relatively unspecialized teeth often are grouped together informally as "peromyscines" to separate them from the larger forms with more complex dentition (Neotoma, Sigmodon). Generally included are Baiomys, Peromyscus, Reithrodontomys, and Onychomys in our region.
Peromyscus—eight species of these fairly small neotomines occur in the New Mexico/Trans-Pecos region. Although they pretty much divide up the ecological habitat, the division frequently is so fine that several species may occur sympatrically. Visible external differences generally involve ear size, foot size, and relative length of the tail. Skeletal differences include some proportions but, among features usually used, the complexity of molars (number and development of subsidiary cusps and styles) and the distinctness of the lower incisive capsule also may be used. The lower incisive capsule is the region of the lower jaw where the incisor originates and may be displayed on the external surface as a nearly smooth area, a slight bulge, or a plainly set-off raised area.
Some of the physical differences are closely associated with behavior. In one study in New Mexico, for example, not only did climbing activity correlate strongly with the length of the tail when interspecific comparisons were made, but individuals within a species tended to climb more or less depending on that individual's tail length. A longer tail apparently (and rationally) improves climbing ability.
Peromyscus boylii (Brush Deermouse) seems to be particularly associated with oaks, and thus limited in most areas to montane or broken country. It occurs throughout much of the Southwest and south in Mexico to near that country's southern border. It seems to spend a considerable amount of time in trees.
Peromyscus crinitus (Canyon Deermouse) is primarily Great Basin south to the head of the Gulf of California, but has an extension east to the Four Corners area and north to extreme southwestern Wyoming. In our area, it is limited to northwestern New Mexico where it lives up to its name in being primarily associated with canyon walls. The subspecies in New Mexico is one of the most beautiful of all the genus, with a blond pelage and relatively long-haired tail.
Peromyscus eremicus (Cactus Deermouse) is an arid-land mouse, mostly coincident with the Chihuahuan Desert in New Mexico. Overall, its range is from southern Nevada and California east at lower elevations through Trans-Pecos Texas and well into Mexico. In the immediate vicinity of El Paso, it occupies two major habitats: open rocky slopes of mountains and sand dune areas that support a fairly good growth of mesquite or other plants. It is one of the most common mice in El Paso.
Peromyscus leucopus (White-footed Deermouse) is not particularly common in El Paso, where it usually occurs in brush along arroyos and probably drainage ditch banks. It is one of the most widely distributed mice in North America.
Peromyscus maniculatus (North American Deermouse), like the White-footed Deermouse, is extremely widespread in North America. In the Southwest, it usually peaks in numbers in the high montane forests, but does occur in virtually all other habitats. It appears to be a form that can take advantage of any opening left in the landscape by other species. As with many other species of rodents in the Southwest, it is prone to large population fluctuations. This was dramatically demonstrated recently when occurrences of hantavirus were tied to high population levels of mouse. Although a number of other cricetid species have been tied to hantavirus, the North American Deermouse remains the most common carrier.
Fig. 1 (right). Rock Deermouse (Peromyscus nasutus): ventral view of skull and dorsal view of lower jaws.
Peromyscus nasutus (Rock Deermouse) is aptly named in that it normally is closely associated with rocks. Lava beds or other areas of jumbled rocks seem to be favorites, mostly from woodland into lower elevations. There is a population in the Franklin Mountains, but at very high elevations.
As frequently happens, names come and go. The Southwestern P. nasutus of past years became P. difficilis (as a separate species from southern populations) and now is back to P. nasutus.
Peromyscus pectoralis (White-ankled Deermouse) is a mouse of southeastern New Mexico and Trans-Pecos Texas and south far into Mexico, with an extension of range through the Hill Country of Texas to near the Oklahoma border. In the Carlsbad area, it is quite common in the ecotonal area between Chihuahuan Desertscrub and woodland in areas that are shallow-soiled and with extensive limestone outcrops.
Peromyscus truei (Piñon Deermouse) is tied very close to Piñon pine woodland. It is one of the more attractive species of the genus with huge ears and a short tail (for the genus). Populations west of the Rio Grande and south of the Interstate 40 have been recognized as a separate species, P. gratus (Osgood's Deermouse), with somewhat smaller ears and some other differing characters.
Last Update: 12 Feb 2008
Centennial Museum and Department of Biological Sciences, The University of Texas at El Paso