MCZ OCCASIONAL PAPERS1- ",Y FEB 2 2 1V91 THE MUSEUM TEXAS TECH UNIVE^iiSFv NUMBER 137 18 FEBRUARY 1991 MAMMALS OF THE ABAJO MOUNTAINS, AN ISOLATED MOUNTAIN RANGE IN SAN JUAN COUNTY, SOUTHEASTERN UTAH Tracy S. Schafer The Abajo Mountains are located in southeastern Utah. A large part of this range and the surrounding valley floor com¬ prise much of the Manti-La Sal National Forest in San Juan County. The Abajo Mountains are completely separated from other mountain ranges, and there is no geological evidence that they ever have been connected to another range (for dis¬ cussion, see Kelson, 1951, and Lee, 1960). The Abajos are bor¬ dered to the north by the desert floor of Canyonlands National Park, to the west by the deeply entrenching Colorado River, to the south by sagebrush flats, and to the east by sagebrush- covered lowlands that extend into western Colorado. Spruce-fir forests with interspersed alpine meadows dominate higher elevations in the Abajos. Some of the high slopes are covered with talus and support little or no vegeta¬ tion. Ponderosa pine, pinon pine, oak, and aspen dominate other communities, which are strongly influenced by soil type as well as elevation. Interspersed juniper occurs frequently throughout pinon pine and oak communities. Kelson (1951) summarized the evidence for the Abajo Moun¬ tains having originated from laccolithic intrusions during the Eocene, which have since been severely eroded. Major dif¬ ferences between the east- and west-facing exposures are evi¬ dent. Eastern exposures have a relatively heavy vegetational cover, whereas the western exposures are more arid; the latter 2 OCCASIONAL PAPERS MUSEUM TEXAS TECH UNIVERSITY are predominantly sandstone, which affects permeability rates. Small reservoirs are scattered throughout the region, along with mountain springs and creeks. Indian Creek, the major permanent stream in the study site, is surrounded by a habitat that supports a lush vegetative cover of grasses and forbs. Durrant (1952) is the most recent comprehensive treatment of mammals from the region. Kelson (1951) investigated ro¬ dent distribution of southeastern Utah, Armstrong (1982) treated the mammals of Canyonlands National Park, and Lee (1960) studied relictual mammalian faunas of isolated moun¬ tain ranges of the area. This study provides the first detailed in¬ vestigation of one of the many isolated ranges. Findings indicate comparable studies of other such ranges are necessary to fully understand the complex island-like zoogeography of the southeastern corner of Utah. Documentation and natural history observations for 31 species of mammals from the Abajo Mountains are presented herein. Some of these are reported for the first time from the range, but equally noteworthy is the conspicuous absence of such taxa as Ochotona, Marmota, Sper- mophilus lateralis, Clethrionomys, Neotoma, Zapus, and Procyon. Methods In 1983 and 1986, Walter W. Dalquest made small collections of mammals in the Abajo Mountains, providing the impetus for a more detailed mammalian survey of them. The most inten¬ sive part of the study was accomplished during six continuous weeks in the field by the author in July and August of 1988. During this period, 2600 trap-nights took 574 small mammals, a trap success rate of 22 percent. Additionally, 78 bats were cap¬ tured during 19 nights of mist netting. Most specimens were prepared as museum study skins accompanied by skulls. The study area encompasses most of the Abajo Mountains (Fig. 1); elevations range from 6400 to 10,360 feet above sea level in the mountains and from selected sites on adjoining Elk Ridge and in the surrounding flats. Species determined to in¬ habit the Abajo Mountains, at least sporadically, are treated in accounts below. Durrant (1952) and Hall (1981) served as points of departure for the known distribution of mammals. All specimens have been deposited in the Collections of Recent Mammals at Midwestern State University and The Museum of Texas Tech University. Tissues of selected individuals SCHAFER—MAMMALS OF THE ABAJO MOUNTAINS 3 109 30 ° ’ Fig. 1.—Collecting localities in the Abajo Mountains as listed in text. Inset shows location of the Abajo Mountains within San Juan County, Utah. were placed in the collection of frozen tissues at Texas Tech University. Following is a numerical listing, from north to south, and west to east, of major collecting localities (as mapped in Fig. 1) in San Juan County, Utah. Elevations (in feet) are given in parentheses following most localities: 9) 7 mi. N Monticello (9180); 5) Foy Lake, 10 mi. WNW Monticello (8690); 6) 9 mi. WNW Monticello (8690); 7) Monticello Lake, 7 mi. WNW Mon¬ ticello (8700); 8) 5 mi. WNW Monticello (8200); 13) 6 mi. W Monticello; 15) 4 mi. W Monticello (8040); 17) Vega Creek, 4 mi. E Monticello (6400); 2) 14 mi. WMonticello (8101); 11) 9 mi. W Monticello (9500); 14) 6 mi. WSW Monticello; 4) Little Dry Mesa, 15 mi. W Monticello (7770); 10) Indian Creek, 10 mi. WSW Monticello (9180); 12) Abajo Peak, 7 mi. WSW Mon¬ ticello (11360); 16) 3 mi. SW Monticello; 1) 19 mi. W Monticello 4 OCCASIONAL PAPERS MUSEUM TEXAS TECH UNIVERSITY (7400); 3) 15 mi. WMonticello (8200); 19) 9 mi. SWMonticello (8200); 18) 13 mi. SWMonticello (7380); 20) 8 mi. SSWMon- ticello (7200); 21) 9 mi. SSW Monticello (7200); 22) 6 mi. N Blanding (6580); 23) 5 mi. N Blanding (6580). Results and Discussion Species Accounts The following species accounts are of mammals for which in¬ formation on occurrence in the Abajo Mountains was ob¬ tained. Systematic order of presentation and vernacular names followjones etal. (1986). Sorex merriami Dobson Merriam’s Shrew Merriam’s shrew is one of the most xeric-adapted of North American Sorex, and commonly inhabits sagebrush desert and shrub steppe throughout its range (Junge and Hoffmann, 1981). One specimen was collected in 1983 by W. W. Dal quest, from a sagebrush community associated with lush grasses along a roadside east of the mountain. Specimen examined (1).—5.5 mi. E Monticello. Sorex monticolus Merriam Montane Shrew This is the most common shrew in the Abajo Mountains and the surrounding valley floor, where more mesic conditions occur. It was particularly abundant along Indian Creek in a spruce-fir community. This is probably the shrew Lee (1960) recorded from the area as S. vagrans obscurus. Specimens examined (14).—Foy Lake, 10 mi. WNW Monticello, 1; 13 mi. W Monticello, 4; 11 mi. W Monticello, 1; 6 mi. WSW Monticello, 1; Indian Creek, 10 mi. WSW Monticello, 7. Sorex nanus Merriam Dwarf Shrew No specimens of the dwarf shrew were taken; the only Utah record is that of Durrantand Lee (1955) from Elk Ridge. SCHAFER—MAMMALS OF THE ABAJO MOUNTAINS 5 Sorexpalustris Richardson Water Shrew Three specimens of Sorex palustris were collected along In¬ dian Creek, largest permanently flowing stream of the range. The specimens were taken along the bank at a site where the creek is about six inches deep and from two to four feet in width. Kelson (1951) declared the water shrew absent from the Abajo Mountains, and Lee (1960) failed to obtain specimens from the area. The only other locality of record was reported by Hall (1981) from North Creek, 7 mi. W Monticello, located three miles northeast of the site at Indian Creek. Specimens examined (3).—Indian Creek, 10 mi. WSW Monticello. Myotis evotis (H. Allen) Long-eared Myotis This long-eared bat inhabits coniferous forests of the western mountains, but apparently is never common (Barbour and Davis, 1969). Specimens of both sexes were collected in July and August, in ponderosa pine and spruce-fir associations. Specimens examined (7).—Indian Creek, 10 mi. WSW Monticello, 3; 13 mi. SW Monticello, 4. Myotis ciliolabrum (Audubon and Bachman) Small-footed Myotis One specimen was taken in a ponderosa pine community im¬ mediately after sunset. The single encounter with this bat sug¬ gests its scarcity in the area, although possibly its slow, fluttering flight enables it to detect and avoid nets. Specimen examined (1).—Indian Creek, 10 mi. WSW Monticello. Myotis volans (H. Allen) Long-legged Bat According to Barbour and Davis (1969), Myotis volans oc¬ cupies a variety of habitats, particularly forested areas, but it seems to be absent from deserts of the Southwest. This bat is easily netted because of its direct flight. Specimens from the study area were captured only in spruce-fir communities. Specimens examined (11).—19 mi. W Monticello, 2; Indian Creek, 10 mi. WSW Monticello, 9. 6 OCCASIONAL PAPERS MUSEUM TEXAS TECH UNIVERSITY Lasionycteris noctivagans (LeConte) Silver-haired Bat Forty-six silver-haired bats, all males, were collected in August; those taken at the end of that month were laden with subcutaneous fat. None was netted at the same locality in July. Males apparently occur in groups, residing in the area for a short time as they build fat reserves to sustain them through autumn migration. Specimens examined (46).—Indian Creek, 10 mi. WSW Monticello. Eptesicus fuscus (Beauvois) Big Brown Bat This species was seldom encountered and appears to be an uncommon resident of the Abajo Mountains. Individuals col¬ lected in late August lacked the fat reserves possessed by Lasionycteris noctivagans. A single female, taken on 21 July 1988, was lactating. Specimens examined (3).—Indian Creek, 10 mi. WSW Monticello, 2; 13 mi. SW Monticello, 1. Lasiurus cinereus (Palisot de Beauvois) Hoary Bat Barbour and Davis (1969) suggested that the sexes of the hoary bat are segregated throughout most of the summer range of the species, and that adult males typically are absent from the maternity ranges of females in the eastern and central United States. During this time, males evidently are limited to the western states (Dalquest, 1943; Findley andjones, 1964). Lasiurus cinereus is common in the Abajo Mountains; several specimens, all males, were netted over small bodies of water in ponderosa pine and spruce-fir communities. Most specimens were taken in July; one was taken in early August. Specimens examined (7).—Indian Creek, 10 mi. WSW Monticello, 1; 13 mi. SW Monticello, 6. Sylvilagus nuttallii (Bachman) Nuttall’s Cottontail Nuttall’s cottontail is uncommon throughout most of the Abajo Mountains. The species was observed only in oak wood¬ lands and communities comprised mostly of antelope brush and rabbit brush at the lower elevations of the mountains and SCHAFER—MAMMALS OF THE ABAJO MOUNTAINS 7 on the valley floor. These habitats offer concealment and food resources lacking in alpine communities at higher elevations. Specimens examined (2).—Monticello Lake, 7 mi. WNW Monticello, 1; Little Dry Mesa, 15 mi. W Monticello, 1. Tamias minimus Bachman Least Chipmunk The least chipmunk is most abundant in oak woodlands, but is also common in ponderosa pine and other communities. It occurs sporadically in spruce-fir forests. As noted by Lee (1960), elevation does not appear to limit its distribution, as Tamias minimus was collected from the lowest to the highest elevations in the study site. Two females collected in mid-July were lactating. Specimens examined (59).—7 mi. N Monticello, 3; Foy Lake, 10 mi. WNW Monticello, 8; Monticello Lake, 7 mi. WNW Monticello, 11; 14 mi. W Monticello, 6; 13 mi. W Monticello, 1; 9 mi. W Monticello, 2; 8 mi. W Monticello, 2; 4 mi. W Monticello, 2; 7 mi. E Monticello, 1; 8 mi. E Monticello, 4; 6 mi. WSW Monticello, 5; Abajo Peak, 7 mi. WSW Monticello, 1; Indian Creek, 10 mi. WSW Monticello, 1; 3 mi. SW Monticello, 3; 9 mi. SW Monticello, 1; 13 mi. SW Monticello, 3; 9 mi. SSW Monticello, 5. Spermophilus variegatus (Erxleben) Rock Squirrel The rock squirrel seems most abundant among rocks, cliffs, and canyons in ponderosa pine and oak communities. In¬ dividuals were seen feeding on fungi, which seems to be a local¬ ly preferred food item and a possible source of moisture. Specimens examined (3).—Little Dry Mesa, 15 mi. W Monticello, 1; 13 mi. WSW Monticello, 1; 9 mi. SW Monticello, 1. Sciurus aberti Woodhouse Abert’s Squirrel Clippings of needle clusters located beneath particular trees were noticed on several occasions, revealing that Sciurus aberti is a rather common resident in ponderosa pine communities. Because of the secretive nature of the species, only two squir¬ rels were seen. Both were observed, on separate occasions, foraging on the ground in a ponderosa pine community. Tamiasciurus hudsonicus was not noted to inhabit this com¬ munity type and the two species seem ecologically segregated in the Abajos. Because Abert’s squirrel is a protected species in 8 OCCASIONAL PAPERS MUSEUM TEXAS TECH UNIVERSITY Utah, none was collected. Lee (1960) listed several specimens from the Abajo Mountains. Tamiasciurns hudsonicus Erxleben Red Squirrel Tamiasciurus hudsonicus is a common resident of the spruce- fir associations in the Abajo Mountains, but seems to be absent from ponderosa pine forests where Sciurus aberti was observed. Lee (1960) reported 16 specimens from the study area. Specimens examined, (3)—Abajo Peak, 7 mi. WSW Monticello, 1; Indian Creek, 10 mi. WSW Monticello, 2. Thomomysbottae (Eydoux and Gervais) Botta’s Pocket Gopher The genus Thomomys is represented by two species in the Abajo Mountains. Thomomys bottae is primarily southern in dis¬ tribution. Where its range overlaps that of T. talpoides, Botta’s pocket gopher typically is restricted to lower elevations, whereas T talpoides inhabits the higher elevations. Thomomys bottae probably is uncommon and is restricted to low elevations in the Abajos. One specimen was trapped in a small meadow among ponderosa pine at an elevation of 7400 feet, and may have come from a relict population distributed along the western exposure of the mountains. The habitat and elevation are otherwise typical of T. talpoides. Specimen examined (1).—19 mi. W Monticello. Thomomys talpoides (Richardson) Northern Pocket Gopher This pocket gopher is widely distributed in the Abajo range. It seems to be nowhere abundant, although Lee (1960) took 39 specimens. Populations appear localized in small areas, par¬ ticularly along grassy roadsides. Mounds were common in small clearings throughout ponderosa pine communities, as¬ sociated with the sandy-loam soils required by the trees. Primarily a gopher of northern distribution, the study site is near the southern extent of the range of the species. Specimens examined (7).—5 mi. WNW Monticello, 1; 14 mi. W Monticello, 2; 8 mi. W Monticello, 2; 4 mi. W Monticello, 1; Indian Creek, 10 mi. WSW Monticello, 1. SCHAFER—MAMMALS OF THE ABAJO MOUNTAINS 9 Castor canadensis Kuhl Beaver Beavers were not seen within the study site, but abandoned beaver ponds were noted along Indian Creek. One of the ponds had large quantities of gnawed wood that obviously had been used to build a dam or lodge. Beaver ponds in the area are probably short-lived due to the heavy accumulations of sedi¬ ment deposited by the spring runoff. Peromyscus boylii (Baird) Brush Mouse Peromyscus boylii evidently is rare in the Abajo Mountains, but may be more common in brushland of the valley floor. Two specimens were collected along a canyon in a community dominated by ponderosa pine and sage. This site, where Peromyscus maniculatuswdLS the most abundant mouse, was lower in elevation than most other collecting localities. Specimens examined (2).—9 mi. SSW Monticello. Peromyscus maniculatus (Wagner) Deer Mouse This mouse is the most abundant mammal in the study area, from the valley floor to the highest peak. Specimens commonly were taken from each trap line and in every habitat type. Oc¬ casional specimens even were collected in the afternoon in traps placed in Microtus runways under dense grassy cover. From mid-July to early August, seven gravid females were col¬ lected that carried from four to five embryos (mean 4.3). Specimens examined {121).—19 mi. SMoab, l;FoyLake, 10 mi. WNW Monticello, 3; 9 mi. WNW Monticello, 8; Monticello Lake, 7 mi. WNW Monticello, 19; 5 mi. WNW Monticello, 5; 19 mi. W Monticello, 1; Little Dry Mesa, 15 mi. W Monticello, 2; 14 mi. W Monticello, 4; 13 mi. W Monticello, 4; 11 mi. W Monticello, 1; 10 mi. W Monticello, 1; Vega Creek, 4 mi. E Monticello, 2; 5.5 mi. E Monticello, 5; 7 mi. E Monticello, 4; 8 mi. E Monticello, 5; 11.5 mi. E Monticello, 1; 6 mi. WSW Monticello, 11; Abajo Peak, 7 mi. WSW Monticello, 9; Indian Creek, 10 mi. WSW Monticello, 9; 3 mi. SW Monticello, 6; 13 mi. SW Monticello, 6; 9 mi. SSW Monticello, 14. Microtuslongicaudus (Merriam) Long-tailed Vole Microtus longicaudus is abundant in suitable habitat of dense grasses along lake shores and streams. Lee (1960) collected 10 OCCASIONAL PAPERS MUSEUM TEXAS TECH UNIVERSITY 124 specimens, all from above 6200 feet in elevation. Many of my specimens were collected in oak communities with little grass understory. This is the most widespread of the two species of voles inhabiting the Abajo range, occuring in a wide variety of habitats. Between mid-July and early August, two lactating females and six gravid females were taken. The number of embryos ranged from four to six (mean 5.2). ’ Specimens examined, (57).—7 mi. N Monticello, 1; Monticello Lake, 7 mi. NW Monticello, 3; Foy Lake, 10 mi. WNW Monticello, 4; 9 mi. WNW Monticello, 2; 11 mi. W Monticello, 5; 4 mi. W Monticello, 1; Vega Creek, 4 mi. E Monticello, 13; 6 mi. WSW Monticello, 3; Indian Creek, 10 mi. WSW Monticello, 17; 3 mi. SW Monticello, 3; 13 mi. SW Monticello, 2; 9 mi. SSW Monticello, 3. Microtus montanus (Peale) Montane Vole The montane vole may be locally abundant where its preferred dense grass cover is present and Microtus longicaudus is absent. On 17 July 1988, a female gave birth to four young in a Sherman live trap. A lactating female and a gravid female containing six embryos were collected in mid-July. Specimens examined (36).—Foy Lake, 10 mi. WNW Monticello, 2; Monticello Lake, 7 mi. WNW Monticello, 2; 13 mi. W Monticello, 13; 11 mi. W Monticello, 1; 7 mi. E Monticello, 3; 6 mi. E Monticello, 1; 5.5 mi. E Monticello, 1; 6 mi. WSW Monticello, 12; Indian Creek, 10 mi. WSW Monticello, 1. Erethizon dorsatum (Linnaeus) Porcupine No porcupines were observed or collected, although trees gnawed on by this species commonly were observed. Canislatrans Say Coyote One animal was observed at an elevation of approximately 8700 feet, and coyotes often were heard howling at elevations between 7000 and 9000 feet. The skulls of four individuals were salvaged from a fur trapper’s carcass dump. The trapper told me they had been trapped on the sage flats north of Monticello. Specimens examined (4).—7 mi. N Monticello.