Terrestrial Mammals of the Riparian Corridor in Big Bend National Park 1

William J. Boeer and David J. Schmidly2

Abstract.--Thirty species of terrestrial mammals inhabit riparian habitats in Big Bend National Park (BBNP), but only one species (the beaver, Castor canadensis) is restricted to these areas. Major changes in the vegetation during the past 30 years, involving an increase in basal and canopy cover, have resulted in the elimination of at least one species (Dipodomys ordii) from the river corridor as well as increased abundance and distribution for two other species (Sigmodon hispidus and Peromyscus leucopus). Compared to the other major plant communities in BBNP, the rodent fauna of the riparian community has lower evenness, richness, and diversity indices (based on the Shannon-Weaver Index). Humqn use and trespass livestock grazing are the major impacts acting upon the natural riparian communities in BBNP today.

INTRODUCTION DESCRIPTION OF THE RIPARIAN CORRIDOR

Mammalian studies of the Big Bend area began Floodplain or riparian vegetation exists with general surveys (Bailey 1905; Johnson 1936; wherever periodic flooding occurs along the Borell and Bryant 1942; and Taylor et al. 1944) Rio Grande in BBNP. These riparian communities designed to identify and document the varied vary from areas a few meters (m) wide to areas fauna of the area. After the park was esta­ extending inland a distance of one kilometer blished, the perspective of mammalian research (km); furthermore, adjacent arroyos and creeks changed somewhat and in recent years studies may carry enough surface or ground water to have concentrated on mammalian autecology and produce a similar floodplain environment. Top­ synecology (Porter 1962; Dixon 1958; and Easter­ ography along the river includes (1) sheer wall la 1973). Most mammalian studies have focused canyons (i.e., Santa Elena and Mariscal canyons on the mammals of the montane woodland and which rise to elevations of 366 m) with few desert grassland habitats. There have been areas of alluvial deposits; (2) long deep canyons no comprehensive studies of riparian mammals. (i.e., Boquillas Canyon) where the walls do not Baccus (1971) investigated the distribution rise abruptly and where larger areas of alluvial of rodents in the park with respect to the major deposits occur; and (3) areas of broad flat physical features, focusing on the effects of floodplain with extensive alluvial deposits. the elimination of grazing on the vegetation and the rodent populations. He also described Denyes (1956) recognized three plant associ­ the similarities and dissimilarities of the ations along the Rio Grande floodplain: (1) the rodent faunas of the woodland, grassland. and riverbank association, consisting of mesquite desert shrub communities; however, he divided (Prosopis juliflora) , seep willow (Baccharis the fauna of the Rio Grande floodplain between sp.), willow (Salix gooddingi) , or cottonwood the desert shrub and grassland communities and (Populus palmeri), located adjacent to areas of did not consider the riparian corridor as a exposed silt and coarse gravel at the water's unique habitat. edge; (2) the Baccharis association, composed of dense stands of seep willow; and (3) the mesquite association, consisting of a thin line 1 Contributed paper. Symposium on the of extensive mesquite trees or an extensive area Importance, Preservation and Management of the of several different plant forms. We have found Riparian Habitat, July 9, 1977, Tucson. Arizona. these three associations to be somewhat altered 2 . from Denyes'description and, although difficult Texas Agricultural Experiment Station, Department of Wildlife and Fisheries Sciences, to document, our general impression is that significant vegetation changes have occurred Texas A&M University, College Station, Texas.

212 \~ .­ l, I in the riparian habitats of BBNP over the past Southern Plains l\'oodrat Neotoma 30 years. The major change is associated with miaropus - C the tremendous increase of salt cedar (Tamarix New World Porcupines - Family ahinensis) along the river. The Baaaharis asso­ Erethizontidae ciation, mentioned by Denyes (1956) as common in Porcupine Erethizon dorsat:wi1 "" R the fine sandy loam soils along the river, is Carnivores - Order Carnivora recognizable today only at a few places (for Dogs and Relatives - Family Canidae example, Black Dike) and appears to have been Coyote Canis Zatrans - C replaced by a mixed mesquite-salt cedar-bermuda Gray Fox Uroayon cinereoargenteus - U grass (cynodon daatyZon) association. Similarly, Raccoons - Family Procyonidae salt cedar also appears to be replacing native Ringtail Bassariscus astutus - U cottonwood and willow trees at many places. Raccoon Proayon Zotor - C Weasels and Relatives - Family Mustelidae Striped Skunk Mephitis mephitis - U MAMMALIAN FAUNA OF THE RIPARIAN CORRIDOR Western Spotted Skunk SpiZogaZe graailis - R Thirty species of terrestrial mammals have Hog-nosed Skunk Conepatus mesoZeuaus - R been either collected or observed in the rip­ Cats - Family Felidae arian habitats of BBNP. These are listed below Mountain Lion FeZis concoZor - R in checklist fashion with their current status Bobcat FeZis rufUS - U (C = common; U = uncommon; R = rare: E = prev­ Even-toed Ungulates - Order Artiodactyla iously present, but no longer occurs; P = pos­ Peccaries - Family Tayassuidae sibly occurs) in the park. Collared Peccary (Javelina) DiaotyZes Pouched Mammals - Order Marsupialia tajaau - U Opossum - Family Didelphidae Deer - Family Cervidae Virginia Opossum DideZphis Mule Deer OdocoiZeus hemionus - U virginiana - P Lagomorphs - Order Lagomorpha During 1975-1976, we sampled small rodents Hares and Rabbits - Family Leporidae at 18 different sites along the riparian corri­ Desert Cottontail SyZviZagus dor. Each site was trapped (using Sherman live auduboni i - C. traps) a total of 720 trap nights resulting in Black-tailed Jack Rabbit Lepus 12,960 trap nights for the entire river corridor. caZifoPniaus - U A total of 1,292 rodents representing two fami­ !s Rodents - Order Rodentia lies (Heteromyidae and Cricetidae) were captured Squirrels - Family Sciuridae as follows (number trapped in parentheses): Texas Antelope Squirrel AmmospermophiZus Family Heteromyidae: Perognathus peniaiZZatus interpres - R (896); Perognathus neZsoni (2); Perognathus Mexican Ground Squirrel SpermophiZus fZavus (5); Dipodomys merriami (65). Family )- mexiaanus - R Cricetidae: Peromysaus Zeucopus (162); Peromyscus Ll Spotted Ground Squirrel SpermophiZus eremiaus (19); Sigmodon hispidus (70); Neotoma 1S spiZosoma - U miaropus (73). Perognathus peniaiZZatus was Pocket Gophers - Family Geomyidae overwhelmingly the most abundant small rodent Tons Yellow-faced Pocket Gopher in the riparian habitats and, for this reason, )t Pappogeomys castanops - C the total density of heteromyid rodents was i.al Pocket Mice - Family Heteromyidae greater than that of cricetid rodents. The Silky Pocket Mouse Perognathus three other heteromyid rodents were relatively fZavus - U rare along the river, although D. merriami was Desert Pocket Mouse Perognathus common at a few sites. Densities of the four Jci­ peniciZZatus - C species of cricetid rodents were more similar the Nelson's Pocket Mouse Perognathus to one another than the densities of the heter­ neZsoni - R omyid species. Peromyscus Zeucopus was the Ord's Kangaroo Rat Dipodomys most common cricetid and P. eremicus the least ordii - E common; Sigmodon hispidus and Neotoma micropus Merriam's Kangaroo Rat Dipodomys occurred in about equal numbers. merriami - C Beaver - Family Castoridae Borell and Bryant (1942) also found Beaver Castor aanadensis - U Perognathus peniaiZZatus to be the most abundant 1e New World Rats and Mice - Family rodent in the riparian corridor. However, com­ rea Cricetidae paring our data with that of Borell and Bryant und Cactus Mouse Peromyscus eremiaus - U (1942) for three other species (Dipodomys :d White-footed Mouse Peromyscus ordii, Peromyscus Zeuaopus, and Sigmodon ult Zeuaopus - C hispidus) reveals that significant changes in Deer Mouse Peromysaus manicuZatus - R abundance and distribution have occurred in Hispid Cotton Rat SigmodOn hispidus - C these species over the past 30 years. These

213 differences correlate with major vegetative attenuatus, we spent eight days (from 4 April changes associated with the cessation of exten­ 1976 to 12 April 1976) trapping at Upper sive livestock grazing. Early accounts (Taylor Tornillo Creek Bridge and other places where et aZ. 1944; Sperry 1938) describe the vegeta­ this species had been previously collected. tion along the river as open and severely Initially, 70 traps were set on both the east over-grazed. However, since ranching activities and west side of Upper Tornillo Creek. Later, ceased at the inception of the park, plant den­ the number of traps was increased to 110 on sities seem to have increased greatly so that the west side and 160 on the east side. The at several places (e.g., Johnson Ranch) mes­ traps were set out in various soil and vege­ quite forests now occur where the river bottom tation types ranging from deep sand·-sparse was once open and sparsely vegetated. Exten­ burro-brush (HymenocZea monogyra) , to packed sive fields of grass also occur today at sites sand-mesquite and gravelly-creosote (Larrea (e.g., Smoky Creek and Coyote) which formerly divaricata) flats. A total of 18 D. ordii were cultivated and farmed. and 21 D. merriami were caught during the first two nights of trapping. Thirty traps Generally, cricetid rodents prefer habitats were also set at Lower Tornillo Creek Bridge with considerable ground cover. Thus, the and 120 were placed along Terlingua Creek increased density of grass and cane (Phragmites where it enters the mouth of Santa Elena communis) along the riparian corridor, as a Canyon. Most of the Lower Tornillo Creek area result of the elimination of grazing, has was a creosote flat with clumps of catclaw served to substantially increase suitable habi­ (Acacia greggz:i) and lechuguilla (Agave tat for these rodents. Two cricetines ZechuguiZla) next to the creek bed. The dry (Sigmodon hispidus and Peromysous Zeucopus) creek bed itself was very rocky and surrounded exemplify this trend. Borell and Bryant (1942) a small knoll of deep sand covered with little collected only four specimens of Sigmodon vegetation. Eight traps were placed on this hispidus along the river among the cane and knoll and 22 in the surrounding flats adjacent cultivated fields around the Johnson Ranch. to the creek bed. A single D. ordii was We recorded 70 cotton rats from 12 different captured on the knoll and nine D. merriami localities along the river in areas where thick were captured on the flats. At Terlingua bermuda grass, cane, and fleabane (Erigeron sp.) Creek, the traps were placed in a sandy area were present. Similarly, Borell and Bryant and 10 D. merriami were captured. (1942) reported taking a few Peromyscus Zeucopus along the river from one mile SW A trapping grid established at Upper Tor­ Boquillas and the Johnson Ranch. Our trapping nillo Creek consisted of 10 lines of 40 traps records indicate that P. Zeucopus is now one per line with each trap 18 m apart; each line of the most common rodents of the riparian was 36 m apart. With regard to vegetation and corridor and this mouse occurs all along the soil, three distinct habitats (designated A, B, river from the mouth of Santa Elena Canyon to and C) were delineated on the grid. Habitat A Rio Grande Village. was on the first floodplain stage adjacent to the creek and consisted of a very open area of Ord's kangaroo rat (Dipodomys ordii) is a deep sandy soil with burro-brush and a few species which apparently has completely dis­ desert willow (ChiZopsis Zinearis) comprising appeared from the riparian corridor during the the dominant vegetation. Habitat B included past 30 years. This species was first reported the second floodplain stage and consisted of a from BBNP in 1939 by M. D. Bryant who described sandy but more compact soil with a moderate a distinct subspecies (D. o. attenuatus) from cover of vegetation including creosote, white­ the mouth of Santa Elena Canyon. In 1944, Dr. thorn (Acacia constricta) , mesquite, burro­ William B. Davis (pers. comm.) collected two brush, grass, and prickly pear (Opuntia sp.). specimens from the type locality and another Habitat C was located on a bench about 3-4 m from the Johnson Ranch. There have been no above habitats A and B. The soil was very additional specimens captured along the Rio compact and the vegetation moderate to thick. Grande since then, although Baccus (1971) Typical desert vegetation, consisting of clumps trapped at the mouth of Santa Elena Canyon, of mesquite, prickly pear, allthorn the Johnson Ranch, and other sites along the (KoeberZinia spinosa), creosote, and.tasajillo river. In over 13,000 trap nights along the (Opuntia ZeptocauZis) were interspersed through­ river, including efforts at the type locality out habitat C. and the Johnson Ranch, we failed to capture a single D. ordii. Baccus (1971), however, did The total number of captures of D. ordii obtain a few specimens from Upper Tornillo and D. merriami for each of the 10 trap lines Creek Bridge (16 km NE Panther Junction), and is presented in Table 1. The percentage of this apparently represents the only remaining captures of D. ordii for each of the three population of this subspecies in BBNP. habitat types was as follows: habitat A, 66.1%; habitat B, 30.6%; habitat C, 3.2%. In order to ascertain the status of D. o. Thus, D. 'ordii was most common in the deep,

214 Table l.--Four day capture totals by trap line for Dipodomys ordii and Dipodomys merriami at Upper Tornillo Creek Bridge. st Habitat Trap Total D. ordii D. merriami Percent Percent er, type line captures captures captures D. ordii D. merriami

A 1 29 25 (40.3)1 4 (5. R)l 86.2 13.8 2 20 16 (25.8) 4 (5.8) 80.0 20.0 d 3 11 3 (4.8) 8 (11.6) 27.3 72.7 4 10 5 (8.1) 5 (7.2) 50.0 50.0 B 5 18 7 (11.3) 11 (15.9) 38.9 61.1 6 11 1 (1.6) 10 (14.5) 9.1 90.0 e 7 8 5 (8.1) 3 (4.3) 62.5 37.5

8 19 0 19 (27.5) 0.0 100.0 rea C 9 5 0 5 (7.2) 0.0 100.0 10 0 0 0 0.0 0.0 y ded 1Represent percent of total catch of D. ordii or D. merriami in a particular trap line. tIe s sandy and sparsely vegetated areas of the first Tornillo Creek in BBNP and no longer occurs ent floodplain stage and decreased in number in along the river or at the type locality. habitats away from the creek bottom. The per­ centage of captures of D. merriami for each of Another mammal affected by vegetative the three habitat types was: habitat A, 11.6%; changes in the riparian corridor is the beaver a habitat B, 50.7%; and habitat C, 37.7%. Thus, which, more than any other mammal in BBNP, is D. merriami was more generally distributed dependent on the riparian corridor for food throughout the three habitats but was much less and shelter. Beaver along the Rio Grande or­ common in habitat A where D. ordii dominated. utilize a variety of plants including cane, ps D. merriami seemed to prefer areas where the seepwillow, willow, and cottonwood. Cotton­ ne soil was more compact or gravelly and the vege­ woods occur today only in park service nurseries and tative cover was greater. at Rio Grande Village and Cottonwood Campground; " B, salt cedars are rapidly replacing cottonwoods t A Dr. William B. Davis trapped at the and willows at other sites. For example, the to Johnson Ranch and the mouth of Santa Elena Gauging Station is one of the few areas where of Canyon in the early 1940's and his description extensive stands of willow still exist, and of the vegetation there is completely different these are currently being used as a food ng from what these areas are like today. Accord­ source by beavers. Nowhere along the river d ing to Davis (pers. comm.) , the river bank at corridor is there any evidence of beaver using f a the Johnson Ranch was a very open sandy area salt cedar. As a result, beavers are literally and was used as a river crossing point for eating themselves out of "house and home" te- Mexicans and cattle. The mouth of Santa Elena because they utilize willow saplings for food Canyon, according to Davis, was also a sandy, and leave only salt cedar saplings which they ) . open area with a considerable growth of will not use. Taylor et aZ.(1944) reported a m Baaaharis. Davis collected Ord's kangaroo rat beaver population of approximately 100 indivi­ at both of these locations. Today, the Johnson duals for the river corridor. However, con­ k. Ranch and the mouth of Santa Elena Canyon are versations with park personnel and the evident umps more like mesquite forests with very little lack of beaver sign along most of the river open terrain. In over 1,500 trap nights at indicate the beaver population today is well 110 these two locations, not a single D. ordii was below the figure reported by Taylor et aZ. ough- captured, although 15 D. merriami (two at (1944). Johnson Ranch and 13 at the mouth of Santa The Shannon-Weaver Index of Diversity Elena Canyon) were collected. In fact, after (Odum 1971) was used to compare the rodent 'ii examining the entire riparian corridor in BBNP, fauna of the riparian community with that of es the only place which seeminly had suitable the woodland, grassland, and desert shrub habi~at for D. ordii was the Gaughing Station. communities in BBNP. This index reveals infor­ Trapping at this site (720 trap nights), however, mation concerning the stability of a community produced 15 D. merriami and no D. ordii. D. in terms of its fauna. Compared to the other ordii attenuatus now seems to be confined to plant communities, the riparian community has the first and second floodplain stages of the lowest evenness, richness, and diversity

215 Table 2.--Shannon-Weaver Index of diversity for the terrestrial rodent fauna of the four major plant communities in BBNP. and im led to vegeta Comnrunities of cot well a canopy Parameters Riparian1 Desert-shrub2 Grassland2 Woodland2 years. result so tha Diversity (li) 1.157 2.008 2.249 1.849 in rip Evenness (e) .465 .783 .793 .771 Sigmod Richness 1.523 1.854 2.912 1.596 (d) increa No. of Species 12 13 17 11 river, common in the lData from Schmidly et al. (1976a, table 20, p. 94). vegeta 2Data from Baccus (1971, table 10, p. 49). caused pass 1 indices (Table 2). In particular, the evenness for 49% of the total backcountry use (in man­ corrid, value (0.465) for the riparian comnrunity is days) in BBNP (Ditton et aZ. 1976). Twenty­ repercl considerably lower than that of the other five percent of this use was float trips on the at cer communities, indicating that one or two species Rio Grande and 24% involved camping at primitive result tend to dominate the rodent fauna of this com­ sites along the River Road. Schmidly et aZ. where, munity. This is evident when examining the (1976b) used correlation analysis to investigate Human total catch figures along the riparian corridor. the relationship among human use, impacts, and conven: The two dominant species of the riparian com­ biological parameters (i.e., rodent fauna and (as re' munity are Perognathus peniciZZatus, with a vegetation) at 18 riparian sites in BBNP. Their stable total of 924 individuals Or 67.7% of the total results revealed a positive and significant and pO! catch, and Peromyscus Zeucopus, with a total of relationship between total subjective human er osc: 162 individuals or 11.9% of the total catch. impact ratings and annual camping use by site (eithe: The grassland is the most diverse community, (man-days). However, the extent of human impact having the highest diversity, evenness, and did not correlate significantly with rodent den­ richness indices as well as the greatest number sities or vegetative parameters at the 18 samp­ of species (17). The desert-shrub, although it ling sites. Thus, correlation analysis revealed only has 13 species (one more than the riparian that site impacts have occurred as a result of TI community), is a more diverse community because recreational use, but not to the point where by the it has a more even distribution, which is indi­ ecological conditions, as indicated by the bio­ CX7005( cated by the fact that the dominant species logical health of the rodent fauna and vegeta­ SouthwE (Perognathus peniciZZatus) in this community tion, are in jeopardy (Schmidly et aZ.1976b). Fe, Ne, accounts for only 38.6% of the total catch as compared to 67.7% for the riparian community. Domestic mammals also occur in the riparian corridor and pose a major problem. The increase in grasses over the past 30 years has provided IMPACTS IN THE RIPARIAN CORRIDOR forage that is not available in the same quan­ tity or quality across the river in Mexico. As In recent years, many riparian areas a result, trespass livestock from Mexico are Baccus, along the Rio Grande have been impacted by human invading the riparian corridor in increasing of activity. Around El Paso and Presidio, man numbers. Grazing by trespass livestock is a dis has destroyed or greatly altered natural riparian constant feature of almost all riparian sites Nat natural habitats through water salvage, cultiva­ and is not confined to one particular region or tat tion and grazing. The International Boundary section of the river. Should this grazing activ­ 114 and Water Commission is presently considering ity continue to increase, it could have dangerous Bailey, a boundary restoration project along the Rio repercussions on the existing vegetation of the N. Grande from Fort Quitman (Hudspeth County) to riparian corridor. Hence, dealing with the Borell, Presidio (Presidio County). This project would livestock problem may prove more difficult for of straighten the channel of the river and result park managers than dealing with human use and Cal in the virtual destruction of riparian habitats impacts which tend to be concentrated in some Bryant, along this stretch of the Rio Grande. areas and virtually absent in others. the of Human use (floating and camping) and tres­ ian pass livestock grazing are the major impacts CONCLUSIONS acting upon the natural riparian communities in BBNP today. In 1975 the Rio Grande accounted Analysis of ,small mammals, vegetation,

216 and impacts along the Rio Grande in BBNP has Denyes, H. 1956. Natural terrestrial communi­ led to five important conclusions: (1) Major ties of Brewster Co., Texas, with special vegetative changes (including the replacement reference to the distribution of mammals. of cottonwoods and willows by salt cedar as Amer. Midland Nat., 55:289-320. well as a tremendous increase in basal and Ditton, R. B., D. J. Schmidly, W. J. Boeer, and canopy cover) have occurred over the past 30 , A. R. Graefe. 1976. A survey and analysis years. (2) These vegetational changes have of recreational and livestock impact on resulted in an alteration of the rodent fauna the riparian zone of the Rio Grande in Big so that certain species which were once rare Bend National Park. Proceedings: River in riparian habitats (i.e., cricetids such as Recreation Management and Research Sympo­ Sigmodon hispidUs and Peromysous leucopus) have sium~ U.S.D.A. Forest Service General increased their numbers and ranges along the Technical Report NC-28:256-266. river, whereas other rodents which were once Dixon, K. L. 1958. Spatial organization in common (Le, Dipodomys ordii) no longer exist a population of Nelson pocket mouse. in the riparian corridor. (3) The increa~e in Southwestern Nat., 3:107-113. vegetative cover, especially grasses, has Easterla, D. A. 1973. Ecology of the 18 caused a reinvasion of domestic livestock (tres­ species of chiroptera at Big Bend National pass livestock from Mexico) into the riparian Park, Texas. The Northwest Missouri State corridor and this may have potentially serious University Studies. Northwest Missouri repercussions on the vegetation. (4) Impacts State Univ., 34:1-165. Ie at certain riparian sites have occurred as a Johnson, M. S. 1936. Preliminary report on lve result of recreational use, but not to the point wildlife survey of Big Bend National Park where ecological conditions are in jeopardy. (proposed), Texas. Ms., p. 1-46 (National ite Human impacts seem to be confined to areas of Park Service). i convenient access. (5) The riparian community Odum, E. P. 1971. Funda;]]€,ntals of Ecology. (as revealed by Shannon-Weaver Index) is less W. B. Saunders Co., Philadelphia, 1.63 pp.

~ir stable than the other major communities in BBNP Porter, R. D. 1962. Movement, populations, and possibly would be more susceptible to great­ and habitat preferences of three species er oscillations resulting from increased impacts of pocket mice (Perognathus) in the Big (either human or livestock). Bend region of Texas. Unpublished Ph.D. act dissertatio::t. Texas A&M Univ., College en- Station, Texas, 255 pp. p­ ACKNOWLEDGMENT Schmidly, D. J., and R. B. Ditton. 1976a. led A Survey and analysis of rec::eational and f This paper is based on research conducted livestock impacts on the riparian zone of by the authors as part of research contract No. the Rio Grande in Big Bend National Park. 0- CX70050442 for the Office of Natural Resources, Report prepared for the Office of Natural Southwest Region, National Park Service, Santa Resources, Southwest Region, National Park Fe, New Mexico. Service, Santa Fe, New Mexico (Contract No. CX70050442), 160 pp. ian Schmidly, D. J., R. B. Ditton, W. J. Boeer, and ase A. R. Graefe. 1976b. Inter-relationships d among visitor usage, human impact, and the LITERATURE CITED biotic resources of the riparian ecosystem As in Big Bend National Park. Paper presented Baccus, J. T. 1971. The influence of a return at the Proc. of First Conference on Scien­ of native grasslands upon the ecology and tific Research in the National Parks, New distribution of small rodents in Big Bend Orleans, Louisiana, November. National Park. Unpublished Ph.D. disser­ Sperry, o. E. 1938. A checklist of the ferns, or tation. North Texas State Univ., Denton, gymnosperms, and flowering plants of the :tiv- 114 pp. proposed Big Bend National Park. Sul Bailey, V. 1905. Biological survey of Texas. Ross State Teachers College Bull., 19(4): N. Amer. Fauna, 25:1-222. 10-98. Borell, A.- E. and M. D. Bryant. 1942. Mammals Taylor, W. P., W. B. McDougall, and W. B. Davis. of the Big Bend region of Texas. Univ. 1944. Preliminary report of an ecological California Publ., Zool., 48:1-62. survey of Big Bend National Park. Report Bryant, M. D. 1939. A new kangaroo rat of of work accomplished March-June, 1944. the D. ordii group from the Big Bend region Administrative report submitted by the of Texas. Occas. Papers Mus. Zool., Louis­ Fish and Wildlife Service to the National iana State Univ., 5:65. Park Service, 9:55 pp (mimeo).

217