Research at the DTRNA

The Desert Tortoise Research Natural Area:

An Important Place for Research and Education

         The Desert Tortoise Research Natural Area (hereafter Natural Area) was formally established as a Research Natural Area and Area of Critical Environmental Concern through Congressional designation and withdrawal from mining, and livestock grazing and through the California Desert Conservation Area Plan in 1980 (U.S. Dept. of the Interior [USDI], Bureau of Land Management [BLM], 1980). The formal designations of Research Natural Area and Area of Critical Environmental Concern have remained in place in subsequent management plans for 35 years (e.g., USDI, BLM and California Department of Fish and Game 1988; USDI BLM 1999, 2006). The fenced area, protected from sheep grazing, recreational vehicles, and mining, offers opportunities for study and conservation unavailable elsewhere in the western Mojave Desert. It is here that students, biologists and research scientists can be assured that their studies can occur in a relatively undisturbed and protected setting. Several graduate students have obtained masters degrees (e.g., Jan Bickett, Matthew Brooks, Bryan Jennings) and doctoral degrees (Ronald W. Marlow, C.C. Peterson) on research conducted at the Natural Area (Marlow 1979, Bickett 1980, Jennings 1993). Published papers from Brooks, Jennings, and Peterson are cited below. Ian Wallis conducted post-doctoral research here (Wallis et al. 1999).

As was intended, the Natural Area has become either the focus of, part of, or one of the databases used in many research projects. Examples include but are not limited to tortoise health (Berry and Christopher 2001, Christopher et al. 1997, 1999, 2003), physiology (Peterson 1994, 1996a, 1996b), diseases (Jacobson et al. 1991, Homer et al. 1998, Brown et al. 1999, Jacobson et al. 2012), growth rings in juveniles (Berry 2002), behavior of juvenile tortoises (Berry and Turner 1986a, 1986b), foraging behavior of adults (Jennings 1993, 1997, 2002), genetics (Murphy et al. 2007; Edwards and Berry 2013), reproduction (Wallis et al. 1999), and anthropogenic impacts (Berry 1978, 1986; Berry et al. 1986,  2012,  2014). The Natural Area is the site of long-term, ongoing studies on demography of desert tortoises spanning >30 years (e.g., Berry and Medica 1995; Berry et al. 1986, 2012; Brown et al. 1999).

Several important scientific advances occurred here. The Natural Area was the site where upper respiratory tract disease, a new and emerging infectious disease caused by Mycoplasma agassizii, was first discovered in wild desert tortoises (Jacobson et al. 1991) and where the first studies on pathogenesis and epidemiology of mycoplasmosis in tortoises were undertaken (Jacobson et al. 1991, Brown et al. 1999, Christopher et al. 2003). The first baseline and comprehensive research program on blood values of healthy tortoises was conducted here and elsewhere in the Mojave Desert (Christopher et al. 1997, 1999); the design and methods were later used to study other imperiled reptiles in the world. The Natural Area was the site where more than 100 dead juvenile tortoises were found, killed by the Common Raven (Campbell 1983). This study was the first to describe a massive kill by Common Ravens. Sheep trampling of juvenile tortoises and potential impacts of sheep grazing on desert tortoises were first described here (Berry 1978) and the detrimental effects of sheep grazing on tortoise presence was later documented (Berry et al. 2014).

The Natural Area is the only area protected from livestock grazing, recreational vehicle use, and other ground- and vegetation-disturbing activities within the geographic range of the Mohave ground squirrel. The distribution of this rare species, endemic to the western Mojave Desert, has been studied on the Natural Area and nearby areas (Leitner 2001, 2005, 2008, 2015; Leitner and Delaney 2014). Genetic studies of variation in Mohave ground squirrels throughout the geographic range indicate that populations on the Natural Area occur between northern and southern genetic types (Bell et al. 2010, Bell and Matocq 2011). Studies of habitat use on a local scale indicate that Mohave ground squirrels are more likely to occur near washes (ephemeral stream channels) where shrubs have higher canopy cover, species richness and diversity than in adjacent areas (Logan 2015).

Other native animals and plants have benefited from protection within the Natural Area.Comparisons of small mammal, lizard, and bird populations inside and outside the Natural Area fence revealed higher abundance and species richness of lizards and birds, and greater diversity and density of kangaroo rats and other small mammals (Brooks 1995, 1999a). Brooks (1995) reported that annual plant biomass, percent cover of perennial shrubs, and seed biomass were generally higher inside fence than outside. Thus, the protected area contributes to greater overall community biomass and diversity. Brooks (1995) conducted research on non-native, invasive plants species and reported that the alien annual grass, Mediterranean or Arab grass, was in higher biomass outside the fence. He also reported that alien annual grasses compete with native annuals and that the alien annual grasses favor certain microhabitats in the desert (Brooks 1999a, 2000). In 2011, the rare and western Mojave Desert endemic wildflower, the Barstow woolly sunflower, was discovered on the Natural Area.

Both long-term and recent landscape-level studies within and adjacent to the Natural Area confirm that the Natural Area contains significantly higher densities of tortoises (Berry et al. 2014) and habitat with fewer recent disturbances than adjacent BLM-managed lands and private lands (Brooks 1995, 1999, Berry et al. 2014). Densities of tortoises in the Natural Area are higher than in critical habitat in the western Mojave Desert in general (Berry et al. 2014; U.S. Fish and Wildlife Service 2015). Factors contributing to the higher tortoise densities and habitat quality include the protective fence, the removal of sheep grazing in the late 1970s and the closure to recreation vehicles and mining in 1980.

Listed below are a few of the published papers, theses and dissertations, as well as a few reports of research conducted at the Natural Area. In summary, the Desert Tortoise Research Natural Area is a very important site for studies and long-term scientific research projects and thus merits special protection for its scientific, educational, and conservation values. It is the only such protected site established specifically as a Research Natural Area in the western Mojave Desert.

Bell, K.C. and M.D. Matocq. 2011. Regional genetic subdivision in the Mohave ground squirrel: evidence of historic isolation and ongoing connectivity in a Mojave Desert endemic. Animal Conservation 14:371-381.

Bell, K.C., D.J. Hafner, P. Leitner, and M.D. Matocq. 2010. Phylogeography of the ground squirrel subgenus Xerospermophilus and assembly of the Mojave Desert biota. J. Biogeography 37:363-378.

Berry, K.H. 1978. Livestock grazing and the desert tortoise. Forty-third North American Wildlife Conference, pp. 505-519.

Berry, K.H. 1986. Incidence of gunshot deaths in desert tortoises in California. Wildlife Society Bulletin 14:127-132.

Berry, K.H. 2002.  Using growth ring counts to age juvenile desert tortoises (Gopherus agassizii) in the wild. Chelonian Conservation and Biology 4:416-424.

Berry, K.H., M.M. Christopher. 2001. Guidelines for the field evaluation of desert tortoise health and disease. Journal of Wildlife Diseases 37:427-450.

Berry, K.H. and P. Medica. 1995.  Desert tortoises in the Mojave and Colorado deserts.  In:  LaRoe, E.T., Farris, G.S., Puckett, C.E., Doran, P.D., and Mac, M.J. (eds.).  Our Living Resources: A Report to the Nation on the Distribution, Abundance, and Health of U.S. Plants, Animals, and Ecosystems. Washington, DC: U.S. Dept. of the Interior, National Biological Service, pp. 135-137.

Berry, K.H., and F. B. Turner. 1984.  Notes on the behavior and habitat preferences of juvenile desert tortoises (Gopherus agassizii) in California.  Proc. Desert Tortoise Council Symposium 1984:111-130.

Berry, K.H., and F.B. Turner. 1986. Spring activities and habits of juvenile desert tortoises, Gopherus agassizii, in California. Copeia 1986:1010-1012.

Berry, K.H. T. Shields, A.P. Woodman, T. Campbell, J. Roberson, K. Bohuski, and A. Karl. 1986. Changes in desert tortoise populations at the Desert Tortoise Research Natural Area between 1979 and 1985. Proc. Desert Tortoise Council Symposium 1986:100-123.

Berry, K.H., L.L. Lyren, J.L. Yee, T.Y. Bailey. 2014. Protection benefits the desert tortoise (Gopherus agassizii) abundance: The influence of three management strategies on a threatened species. Herpetological Monographs 28:66-92.

Berry, K.H., T. Shields, and L. Lyren. 2013. Management implications of protective fencing:  A comparison of desert tortoise and predator populations at and near the Desert Tortoise Research Natural Area Interpretive Center Plot, Kern County, California, in 2012.  Report from the U.S. Geological Survey to the U.S. Bureau of Land Management, Sacramento, California.  35 pp.

Bickett, J. 1980.  Aspects of the natural history of the desert tortoise, Gopherus agassizii, in southeastern California. M.A. Thesis. California State University, Sacramento.

Brooks, M.L. 1995.  Benefits of protective fencing to plant and rodent communities of the western Mojave Desert, California. Environmental Management 19:65-74.

Brooks, M.  1999a.  Effects of protective fencing on birds lizards, and black-tailed hares in the western Mojave Desert. Environmental Management 23:387-400.

Brooks, M.L. 1999b. Habitat invisibility and dominance by alien annual plants in the western Mojave Desert. Biological Invasions 1:325-337.

Brooks, M.L. 2000. Competition between alien annual grasses and native annual plants in the Mojave Desert. American Midland Naturalist 144(1):92-108.

Brown, M.B., K.H. Berry, I.M. Schumacher, K.A. Nagy, M.M. Christopher, and P.A. Klein. 1999. Seroepidemiology of upper respiratory tract disease in the desert tortoise in the western Mojave Desert of California. Journal of Wildlife Diseases 35:716-727.

Busack, S.D., and R.B. Bury. 1974. Some effects of off-road vehicles and sheep grazing on lizard populations in the Mojave Desert. Biological Conservation 6:179-183.

Campbell, T. 1983. Some natural history observations of desert tortoises and other species on and near the Desert Tortoise Natural Area, Kern County, California.  Proc. Desert Tortoise Council Symposium 1983: 80-88.

Christopher, M.M., K.A. Nagy, I. Wallis, J.K. Klaassen, and K.H. Berry. 1997. Plenary Lecture. Laboratory health profiles of desert tortoises in the Mojave Desert: A model for health status evaluation of chelonian populations. Pages 76-82 in J. Van Abbema (ed.). Proceedings: Conservation, Restoration, and Management of Tortoises and Turtles—An International Conference. New York Turtle and Tortoise Society and WCS Turtle Recovery Program, USA.

Christopher, M.M., K.H. Berry, I.R. Wallis, K.A. Nagy, B.T. Henen, and C.C. Peterson. 1999.  Reference intervals and physiologic alterations in hematologic and biochemical values of free-ranging desert tortoises in the Mojave Desert. Journal of Wildlife Diseases 35:212-238.

Christopher, M.M., K.H. Berry, B.T. Henen, and K.A. Nagy.  2003.  Clinical disease and laboratory abnormalities in free-ranging desert tortoises in California (1990-1995). Journal of Wildlife Diseases 39:35-56.

Edwards, T., and K.H. Berry. 2013. Are captive tortoises a reservoir for conservation? An assessment of genealogical affiliation of captive Gopherus agassizii to local, wild populations. Conservation Genetics 14:649-659.

Henen, B.T., C.C. Peterson, I.R. Wallis, K.H. Berry, and K.A. Nagy. 1998. Effects of climatic variation on field metabolism and water relations of desert tortoises.  Oecologia 117:365-373.

Homer, N.L., K.H. Berry, M.B. Brown, G. Ellis, and E.R. Jacobson. 1998. Pathology of diseases in wild desert tortoises from California. Journal of Wildlife Diseases 34(3):508-523.

Jacobson, E.R., J.M. Gaskin, M.B. Brown, R.K. Harris, C.H. Gardiner, J.L. LaPointe, H.P. Adams, and C. Reggiardo. 1991.  Chronic upper respiratory tract disease of free ranging desert tortoises (Xerobates agassizii). J. Wildlife Diseases 27:296-316.

Jacobson, E.R., K.H. Berry, J. F.X. Wellehan Jr., F. Origgi, A.L. Childress, J. Braun, M. Schrenzel, J. Yee, and B. Rideout. 2012. Serologic and molecular evidence for Testudinid herpesvirus 2 infection in wild Agassiz’s desert tortoises, Gopherus agassizii. Journal of Wildlife Diseases 48:747-757.

Jacobson, E.R., M.B. Brown, L.D. Wendland, D.R. Brown, P.A. Klein, M.M. Christopher, and K.H. Berry. 2014. Mycoplasmosis and upper respiratory tract disease of tortoises: A review and update. The Veterinary Journal 201:257-264.

Jennings, W.B.  1993.  Foraging ecology of the desert tortoise (Gopherus agassizii) in the western Mojave Desert. M.S. Thesis. University of Texas, Arlington, Texas.  89 pp.

Jennings, W.B. 1997. Invasions of exotic plants: implications for the desert tortoise, Gopherus agassizii, and its habitat in the western Mojave Desert. Pages 10-12, in J.  Van Abbema (ed.). Proceedings: Conservation, Restoration, and Management of Tortoises and Turtles—An International Conference. NewYork Turtle and Tortoise Societyand WCS Turtle Recovery Program, USA.

Jennings, W.B. 1997. Habitat utilization of the desert tortoise, Gopherus agassizii, in the western Mojave Desert and impacts of off-road vehicles.  Pages 42-45 in J.  Van Abbema (ed.). Proceedings: Conservation, Restoration, and Management of Tortoises and Turtles—An International Conference. NewYork Turtle and Tortoise Societyand WCS Turtle Recovery Program, USA.

Jennings, W.B. 2001. Comparative flowering phenology of plants in the western Mojave Desert. Madroño, Vol. 48, No. 3 pp. 162-171.

Jennings, W.B. 2002. Diet selection by the desert tortoise in relation to the flowering phenology of ephemeral plants. Chelonian Conservation and Biology 4:353-358.

Jennings, W.B., and K.H. Berry. 2015. Desert tortoises (Gopherus agassizii) are selective herbivores that track the flowering phenology of their preferred food plants. PLOS One 10(1):e0116716. doi:10.1371/journal.pone.0116716.

Leitner, P. 2001. California Energy Commission and Desert Tortoise Preserve Committee, Mohave Ground Squirrel Study, Final Report, 1998-2000. Prepared for Desert Tortoise Preserve Committee, Inc., Riverside, CA. 33 pp + append.

Leitner, P.  2005. Trapping survey for the Mohave ground squirrel in the DTNA Eastern Expansion Area, 2003. Prepared for Desert Tortoise Preserve Committee, Inc., Riverside, CA. 19 pp.

Leitner, P. 2008. Current status of the Mohave Ground Squirrel. Transactions of the Western Section of The Wildlife Society 44:11–29.

Leitner, P. 2015. Current status of the Mohave ground squirrel (Xerospermophilus mohavensis): A five-year update (2008-2012). Western Wildlife 2:9-22.

Leitner, P. and D.K. Delaney. 2014. Mohave ground squirrel camera study, 2011-2012: Final report to California Department of Fish and Wildlife. Prepared for California Department of Fish and Wildlife, Sacramento, CA. 10 pp.

Leitner, P., M.D. Matocq, and K.C. Bell. 2011. Genetic analysis of Mohave ground squirrels from the Desert Tortoise Research Natural Area. Prepared for Desert Tortoise Preserve Committee, Inc., Riverside, CA. 12 pp.

Logan, M.K. 2015. Assessing site occupancy of Mohave ground squirrels: Implications for conservation. Journal of Wildlife Management 2015; DOI: 10.1002/jwmg.1011.

Marlow, R.W. 1979. Energy relations in the desert tortoise, Gopherus agassizii. Ph.D  Dissertation, University of California, Berkeley.  Univ. Microfilms International, Ann Arbor, Michigan. No. 8014797.

Morafka, D.J., K.H. Berry, and E.K. Spangenberg. 1997. Predator-proof field enclosures for enhancing hatching success and survivorship of juvenile tortoises: A critical evaluation. Pages 147-165 in J. Van Abbema (ed.), Proceedings: Conservation, Restoration, and Management of Tortoise and Turtles—An International Conference. New York Turtle and Tortoise Society and WCS Turtle Recovery Program, USA.

Mullen, E.B., and P. Ross. 1997. Survival of relocated tortoises: Feasibility of relocating tortoises as a successful mitigation tool. Pages 140-145 in J. Van Abbema (ed.). Proceedings: Conservation, Restoration, and Management of Tortoises and Turtles—An International Conference. N.Y. Turtle and Tortoise Society and WCS Turtle Recovery Program, USA.

Murphy, R.W., K.H. Berry, T. Edwards, and A. M. McLuckie. 2007.  A genetic assessment of the recovery units for the Mojave population of the desert tortoise, Gopherus agassizii.  Chelonian Conservation and Biology 6:229-251.

Peterson, C.C. 1994. Different rates and causes of high mortality in two populations of the threatened desert tortoise Gopherus agassizii.  Biological Conservation 70:101-108.

Peterson, C.C. 1996a. Anhomeostasis:  seasonal water and solute relations in two populations of the desert tortoise (Gopherus agassizii) during chronic drought. Physiological Zoology 69:1324-1358.

Peterson, C.C. 1996b. Ecological energetics of the desert tortoise (Gopherus agassizii): effects of rainfall and drought. Ecology 77:1831-1844.

U.S. Depart. of the Interior, Bureau of Land Management. 1980. California Desert Conservation Area Plan 1980.  Bureau of Land Management, Riverside, California.

U.S. Dept. of the Interior, Bureau of Land Management.  1999.  The California Desert Conservation Area Plan of 1980, as amended.  U.S. Department of the Interior, Bureau of Land Management, Desert District, Riverside, California, USA.

U.S. Dept. of the Interior, Bureau of Land Management.  2006.  Record of Decision, West Mojave Plan, Amendment to the California Desert Conservation Area Plan.  March 2006.  U. S. Department of the Interior, Bureau of Land Management, California Desert District, Moreno Valley, California.

U.S. Dept. of the Interior, Bureau of Land Management and California Dept. of Fish and Game. 1988.  A Sikes Act Management Plan for the Desert Tortoise Research Natural Area and Area of Critical Environmental Concern. U.S. Bureau of Land Management, Ridgecrest, California.

U.S. Fish and Wildlife Service.  2010.  Mojave Population of the Desert Tortoise (Gopherus agassizii), 5-Year Review:  Summary and Evaluation.  U.S. Fish and Wildlife Service, Desert Tortoise Recovery Office, Reno, Nevada.  Sept. 30, 2010. 121 pp.

U.S. Fish and Wildlife Service. 2015. Range-wide Monitoring of the Mojave Desert Tortoise (Gopherus agassizii):  2013 and 2014 Annual Reporting. Report by the Desert Torotise Recovery Office, U.S. Fish and Wildlife service, Reno, NV. 44 pp.

Wallis, I.R., B.T. Henen, and K.A. Nagy. 1999. Egg size and annual egg production by female desert tortoises (Gopherus agassizii): the importance of food abundance, body size, and date of egg shelling. Journal of Herpetology 33:394-408.