DESERT BIGHORN SHEEP: A GUIDE TO SELECTED MANAGEMENT PRACTICES

Transcription

1 BIOLOGICAL REPORT 88(35) SEPTEMBER 1988 DESERT BIGHORN SHEEP: A GUIDE TO SELECTED MANAGEMENT PRACTICES Fish and Wildlife Service U.S. Department f the nterir DISTRIBUTION STATEMENT A Apprved fr public release; Distributin Unlimited imc QUALITY DJSPECTSD 1

2 Bilgical Reprt This publicatin series f the Fish and Wildlife Service cmprises reprts n the results f research, develpments in technlgy, and eclgical surveys and inventries f effects f land-use changes n fishery and wildlife resurces. They may include prceedings f wrkshps, technical cnferences, r sympsia; and interpretive bibligraphies. They als include resurce and wetland inventry maps. Cpies f this publicatin may be btained frm the Publicatins Unit, U.S. Fish and Wildlife Service, Washingtn, DC 20240, r may be purchased frm the Natinal Technical Infrmatin Service (NTIS) 5285 Prt Ryal Rad, Springfield, VA Library f Cngress Catalging-in-Publicatin Data Smith, Nrman S. Desert bighrn sheep. (Bilgical reprt; 88(35)) "May, 1988." Supt. f Dcs, n.: /2:88(35) 1. Bighrn sheep Eclgy. 2. Wildlife management. 3. Mammals Eclgy. I. Krausman, Paul R., II. Kirby, Rnald E. HI. Title. IV. Series: Bilgical reprt (Washingtn, D.C.); QL737.U53S This publicatin may be cited as fllws: Smith, N. S., and P. R. Krausman Desert bighrn sheep: A guide t selected management practices. A literature review and synthesis including appendixes n assessing cnditin, cllecting bld, determining age, cnstructing water catchments, and evaluating bighrn range. U.S. Fish Wildl. Serv., Bil. Rep. 88(35). 27 pp.

3 Bilgical Reprt 88(35) September 1988 Desert Bighrn Sheep: A Guide t Selected Management Practices A Literature Review and Synthesis Including Appendixes n Assessing Cnditin, Cllecting Bld, Determining Age, Cnstructing Water Catchments, and Evaluating Bighrn Range by Nrman S. Smith U.S. Fish and Wildlife Service Arizna Cperative Fish and Wildlife Research Unit 210 Bilgical Sciences Building East University f Arizna Tucsn, AZ and Paul R. Krausman Schl f Renewable Natural Resurces 325 Bilgical Sciences Building East University f Arizna Tucsn, AZ Prject Officer Rnald E. Kirby U.S. Fish and Wildlife Service Office f Infrmatin Transfer 1025 Pennck Place, Suite 212 Frt Cllins, CO U.S. Department f the Interir Fish and Wildlife Service Washingtn, DC 20240

4 Frewrd Perhaps n ther ungulate has s many scieties specifically dedicated t its preservatin and management as des the bighrn sheep. Many f these are yet mre specific in that they emphasize the bighrn sheep f the Suthwest, the desert bighrn. Cncern fr desert bighrns is manifest in bth State and Federal effrts in their management and cnservatin. In particular, because the majrity f these animals are n Federal lands, nt nly are several Federal agencies as well as the States invlved in management, but als invlved are the many citizens wh make use f these same lands fr recreatin, mineral extractin, and ther 20th century activities. Management fr the desert bighrn is f particular imprtance n several Natinal Wildlife Refuges managed by the U.S. Fish and Wildlife Service: Cabeza Prieta, Havasu, Imperial, and Kfa Natinal Wildlife Refuges, Arizna; San Andres Natinal Wildlife Refuge, New Mexic; and Desert Natinal Wildlife Range, Nevada. The Office f Infrmatin Transfer, in ne f its regular queries f management persnnel regarding their current infrmatin needs, received a request frm the Assistant Reginal Directr Refuges and Wildlife in Albuquerque, NM (Regin 2) and his Refuge supervisry and statin staff in New Mexic and Arizna fr assistance in pulling tgether sme disparate infrmatin n desert bighrns that culd simultaneusly serve several purpses. These included: (1) a cmprehensive review f prtins f the literature n desert bighrn sheep; (2) a synthesis f current literature n selected tpics; and (3) a discussin f what were judged t be pririty management and research needs fr desert bighrn sheep based n the results f this literature review and synthesis. The expected values f this exercise were likewise threefld: (1) a view f the situatin frm the perspective f persns utside the current management and research cmmunity wuld be btained; (2) ideas useful fr cnsideratin by thse planning bth current and future management and research wuld be listed; and (3) a cncise dcument useful as an rientatin package t several imprtant desert bighrn sheep management issues wuld be available fr use in the Suthwest. This Bilgical Reprt addresses fur tpics selected by the staff f Regin 2 as imprtant and cntinuing cncerns fr desert bighrn sheep managers: water requirements f the species; effects f human activity n desert bighrns; desert bighrn disease and its cntrl; and interspecific relatins f bighrns and ther desert ungulates. In additin, fur appendixes reviewing data gathering prcedures and specific management fr bighrn sheep ppulatins and their habitat are prvided. The intent thrughut was t prvide a succinct synthesis and t prvide entry t the nw substantial literature n the species. This dcument is an excellent starting pint fr review f desert bighrn management issues, and is anther view f fur desert bighrn management cncerns that will prve useful in management and research planning fr the species. Rnald E. Kirby Office f Infrmatin Transfer Research and Develpment in

5 Preface The desert bighrn sheep has been studied fr many years and these studies have slved many management prblems. Research has als identified the need fr additinal slutins t new r anticipated prblems. This guide addresses sme recent management practices and prblems, suggests sme techniques, discusses pssible slutins, and identifies tpics fr further research. The scpe f the guide includes a review f water requirements f desert bighrn sheep, the effects f man's activities and disease n desert bighrns, and the interspecific relatins f sheep and ther animals. Identificatin f needed infrmatin is an imprtant part f this guide. Our recmmendatins d nt cver all f the research needed, but identify sme f the mst pressing needs. Permissin t include cpyrighted material in this paper was btained frm V. Geist, H. E. McCutchen, and the University f Arizna Press. The cver illustratin was drawn frm an riginal phtgraph by N. S. Smith. IV

6 Summary This guide summarizes pertinent literature n fur tpics f desert bighrn sheep eclgy and management: (1) their water requirements and adaptatins are cmpared with thse f ther desert-dwelling ungulates; (2) the effects f human activities such as mining, paching, hunting, ranching, hiking, and urban encrachment are discussed; (3) diseases and disease cntrl, specifically scabies and desert bighrn chrnic sinusitis, are reviewed; and (4) the relatin f bighrn sheep t ther resident wildlife is addressed. Recmmendatins fr management and research are included in each sectin. Finally, appendixes prvide infrmatin n hw t assess physical cnditin, cllect bld, classify the age f sheep, cnstruct water catchments, and sample vegetatin.

7 Cntents Page Frewrd m Preface iv Summary v Acknwledgments vii Intrductin 1 Taxnmy and Distributin 1 Descriptin 1 Habitat 2 Eclgy 2 Reprductin 2 Fd 2 Mrtality Factrs 2 Management 3 Water Requirements 3 Anatmical Adaptatins 3 Physilgical Adaptatins 3 Behaviral Adaptatins 4 Management Recmmendatins 4 Research Recmmendatins 5 Effects f Human Activity n Desert Bighrn Sheep 5 Examples f Management Restrictins 5 Limited Access t Kfa 5 Santa Catalina Muntains and Dg Cntrl 5 Management Recmmendatins 6 Disease and Its Cntrl 6 A Perspective fr Disease Evaluatin 6 Recent Disease Prblems 7 Scabies 7 Desert Bighrn Chrnic Sinusitis (DBCS) 7 Management Recmmendatins 7 Research Recmmendatins 8 Interspecific Relatins 8 Cmpetitin 8 Predatin 9 Management Recmmendatins 9 Research Recmmendatins 9 Synpsis 9 References 11 Appendix A. Visually Assessing Physical Cnditin f Bighrn Sheep 17 Appendix B. Cllecting Bld frm Bighrn Sheep 18 Appendix C. Age Classificatin f Bighrn Sheep 19 Appendix D. References t the Cnstructin and Develpment f Water Catchments fr Bighrn Sheep Appendix E. Vegetatin Sampling 24 VI

8 Acknwledgments Our gratitude is wed t the many naturalists, bilgists, and wildlife managers wh cmpiled infrmatin and published that wisdm. A. V. Sandval gave us valuable infrmatin nt yet published. H. E. McCutchen, V. Geist, and the University f Arizna Press are thanked fr prviding permissin t use cpyrighted material. We als thank Valery Catt fr typing the manuscript. Funding fr cmpiling this Bilgical Reprt was furnished by the Cperative Fish and Wildlife Research Units Center, Washingtn, DC, and the Arizna Cperative Fish and Wildlife Research Unit. Csts f publicatin and prject management were brne by the Office f Infrmatin Transfer. VII

9 Intrductin Desert bighrn sheep (Ovis canadensis cremnbates, O. c. mexicana, O. c. nelsni, O. c. weemsi) are imprtant and highly desirable desert ungulates. The emtins elicited by these sheep in desert bighrn hunters, natural histrians, bilgists, recreatinists, and pliticians are prbably nly surpassed by thse arising frm the cntrversies ver cytes (Canis latrans). Large sums f mney, time, and effrt are expended t manage, study, preserve, hunt, and enjy these animals. Despite the best intentins and effrts f State and Federal agencies, universities, and private rganizatins, there remain many unanswered questins and unreslved management prblems cncerning desert bighrns. Our intent in this guide is t summarize and synthesize what is knwn abut several aspects f desert bighrn eclgy and management. In particular, we address water requirements f the species, effects f human activity, disease, and interspecific relatins. Where apprpriate, we nte which tpics need additinal research and we make recmmendatins fr management. In several appendixes, we prvide infrmatin that may be used t gather data necessary fr making management decisins. Taxnmy and Distributin Bighrn sheep are in the Order Artidactyla, Family Bvidae. There are six existing subspecies f Ovis canadensis: O. c. califrniana, O. c. canadensis, O. c. cremnbates, O. c. mexicana, O. c. nelsni, and O. c. weemsi. Desert bighrn sheep include the fur subspecies that typically inhabit dry and barren muntain ranges: cremnbates, mexicana, nelsni, and weemsi. Hwever, sheep in the suthern prtins f the range f califrniana and canadensis may als be cnsidered desert bighrn because their habitat is dry and barren (Manville 1980). Histrically, abut ne millin desert bighrn sheep inhabited the desert muntain ranges f the suthwestern United States (Buechner I960; Cperrider 1985). Hwever, habitat alteratin and destructin by man have eliminated r reduced herds t the pint that fewer than 12,000 desert bighrn sheep exist in islated ppulatins scattered thrughut their frmer range (Mnsn 1980). The subspecies f desert bighrn sheep are distributed thrughut the Suthwest (Figure 1). Reintrductin prgrams have increased the current range f the desert bighrn in Arizna, Califrnia, Clrad, Nevada, New Mexic, Texas, and Utah (Weaver 1986). Descriptin Large, recurving hrns are a distinguishing feature f bighrn sheep. Hrns f adult males are massive and curled frward beside the face and, tgether with the skull may represent ver 10% f ttal bdy mass (Bld Figure 1. Apprximate distributin f races f bighrn sheep. Desert bighrn sheep include weemsi, cremnbates, mexicana, nelsni, and suthern prtins f the range f califrniana and canadensis. The Audubn bighrn (0. c. audubni) is extinct. The small circles indicate type lcalities. (Reprinted by permissin frm the University f Arizna Press, Tucsn in G. Mnsn and L. Sumner, eds. The desert bighrn. University f Arizna Press, Tucsn.) et al. 1970; Geist 1971). Females als have hrns, but theirs are nt as large r curved as thse f males. Hrns f males are as lng as 305 mm (Wishart 1978). Desert bighrn sheep have smaller bdy sizes than ther muntain sheep, but they have the largest hrns. Adult males are cm at the shulders, abut 150 cm lng, and weigh abut kg. Females are smaller than males and weigh abut 50 kg. Clr varies between reddish brwn and dark chclate, and desert sheep usually have a white muzzle, rump patch, psterir f legs and belly. There is n neck ruff (Shackletn 1985). Adult females in their prime are well-prprtined, have an erect head, and a runded rump and pelvic regin. Prime males have a thick, blcky appearance, 1

10 and are t heavy in bdy t be cnsidered well-prprtined (Hansen 1980). Habitat Desert bighrn habitat is usually rugh, rcky, and brken by canyns and washes (Hansen 1980). Cmpnents f bighrn habitat include frage, escape cver, bedding areas, lambing and rutting areas, thermal cver, and water (Hansen 1980; Krausman and Lepld 1986). Vegetative cmmunities used by desert sheep range frm upland pinyn (Pinus edulis)-juniper (Juniperus spp.) (Brwning and Mnsn 1980) t desert scrub (e.g., crestebush [Larrea tridentata]-ragwee.d \Ambrsia spp.] cmmunities). Eclgy Reprductin Desert bighrn sheep are prmiscuus. Males and females are sexually mature at 18 m, althugh females usually d nt breed until they are 2.5 yr ld (Wishart 1978). The gestatin perid is d (Wishart 1978; Turner and Hansen 1980). Cpulatin usually ccurs between July and December, and lambs are brn frm January thrugh June. Lambing and breeding dates vary by lcatin. Weights f captive lambs at birth are kg (Blunt et al. 1977; Geist 1971; Hansen and Deming 1980). Lambs are usually weaned at 4-6 m (Geist 1971). The bighrn sheep exhibits a wide spectrum f scial behavir patterns and is ne f the mst scially active Nrth American ungulates (Shackletn 1985). Bighrn sheep live in grups, but fr mst f the year adult males usually live apart frm females and yung (Geist 1971). Male and maternal grups ften ccupy separate hme ranges. Grup size varies (n = 2-9) with seasn and amng ppulatins (Bld 1963; Chilelli and Krausman 1981). Males assciate with maternal grups during rut. During the rest f the year males are nt excluded but leave maternal grups t jin male grups, where they then becme physically and scially dminant t adult females (Geist 1971). Scial status f males is funded n hrn size and fighting ability (Geist 1971). Maintenance and cmfrt behavir includes stretching, shaking, rubbing, scratching, urinating, and defecating. Females squat t urinate; males stand; and all sheep stand during defecatin (Shackletn 1985). Desert bighrn sheep are active thrughut the day althugh mst activity is diurnal (Chilelli and Krausman 1981; Krausman et al. 1985; Alderman et al. 1988). Daily activity patterns cnsist f alternate feeding and rest-ruminatin buts (Chilelli and Krausman 1981; Alderman et al. 1988). Feeding is cncentrated near dawn and dusk but varies depending n habitat quality, energy requirements, physilgical cnditin, and scial rganizatin (Eccles 1981). Scial-behavir patterns in bighrn sheep are imprtant (Geist 1971) and develp as sheep mature (2-3 yr fr females; 6-7 yr fr males). Learning is imprtant fr dminance relatins amng males because males recgnize ther individuals and develp scial status by viewing hrns f ther males (Geist 1971). Fd Desert bighrn sheep are adaptable fragers; their diet is related t the habitat ccupied. Generally, desert bighrn sheep cnsume grass when available. When grasses becme limited, brwse and frbs assume greater imprtance (Brwn et al. 1977; Brwning and Mnsn 1980). Minerals are btained frm natural salt-licks r frm artificial blcks prvided by game managers. Desert bighrns can exist n ranges withut freestanding water (Krausman et al. 1985; Alderman et al. 1988), but mst ppulatins have access t surface water. Mrtality Factrs Parasites, disease, cmpetitin, predatin, accidents, mineral and dietary deficiencies, and abnrmal climatic cnditins cntribute t mrtality f desert bighrn sheep. The nematde lungwrm (Prtstrngylus stilesi) that has influenced nrthern subspecies f bighrn sheep has nt affected desert bighrn sheep (Allen 1980). Hwever, desert subspecies are susceptible t a variety f bacterial and parasitic infestatins (e.g., Escherichia cli, Pasteurella spp., Crynebacterium spp.). Numerus parasites infest desert bighrn sheep (e.g., Oestrus vis, which has been implicated with desert bighrn chrnic sinusitis). Cmpetitin cntributes t mrtality when limited habitat is used by ther grazing ungulates (Wishart 1978). The carrying capacity f bighrn habitat can be reduced due t resurce cmpetitin amng bighrn herds and ther large ungulates (e.g., burrs [Equus asinus], desert mule deer [Odcileus heminus crki], and livestck; Wishart 1978; Krausman and Lepld 1986). The negative effects f dmestic livestck n desert bighrn sheep are well dcumented (see Disease and Its Cntrl and Interspecific Relatins sectins). Desert bighrn sheep are preyed n by cytes, muntain lins (Felis cnclr), bbcats (Lyivc mfiis), eagles (Haliaeehis leuccephalus and Aquila chrysaets) (Wishart 1978; Kelly 1980), gray fx (Urcyn cinereargenteus), jaguar (Panthern nca), and celt (Felis pardalis). Predatin is limited due t the precarius habitats desert sheep use; hwever, that same habitat cntributes t mrtality frm falls (Wishart 1978; Allen 1980). Other reprted accidents include being trapped in dry waterhles, fights between males, lightning strikes, and rad kills. Inbreeding may cntribute t mrtality in islated, small ppulatins that characterize many desert bighrn ppulatins.

11 Management Management f desert bighrn sheep has evlved thrugh three phases: (1) a custdial phase characterized by restricting hunting and establishing refuges; (2) btaining better inventries and experimentatin with water develpments and animal handling; and (3) pening limited hunting (Weaver 1986). An additinal phase wuld be the reestablishment f bighrn sheep thrughut their histric range. Mst States are actively reestablishing herds f sheep n ranges frm which they have been eliminated. Additinal management effrts fcus n frage imprvement (e.g., burning, chaining, use f herbicides), reductin f cmpetitin and habitat imprvement (i.e., water develpments; Graf 1980). Water Requirements All desert animals need water. The adaptatins f desert species t btain, use, and cnserve water maybe anatmical, physilgical, behaviral, r sme cmbinatin f the three. Anatmical mdificatins assciated with successful desert mammals include: clr r pattern f clrs f the cat; density f hair; shape f bdy r extremities; kidney structure; cartid artery lcatin and assciatin with a cled venus netwrk frm the nasal area; and length f the water reabsrptive prtin f the large intestine. Physilgical adaptatins include: methds f cncentrating urine; extracting water frm feces; extracting prefrmed water frm fd; prducing metablic water by the xidatin f fats and carbhydrates; dehydratin tlerance; fluctuatin f bdy temperature; differential regulatin f bdy and brain temperatures; and lwering f metablism. Behaviral activities that allw mammals t ccupy hstile desert envirnments include: aviding heat by ncturnal r crepuscular activity; seeking clest r mst humid shelters; seasnal migratin r daily mvements t seek water r avid drught; diet selectin fr succulent fd r plants that have absrbed misture r are dew-laden at night; and rientatin f bdy relative t the sun's rays. The majr methd by which large mammals regulate bdy temperature evaprative cling requires water, and a large part f the water lst by mammals is fr this use. Cnsequently, when discussing water requirements f desert bighrns we must cnsider hw they regulate their bdy temperature. (Fr a review f desert adaptatins see: Schmidt-Nielsn [1964]; Taylr 1969; Maliy [1972].) In this sectin we summarize the literature n the water requirements f desert bighrn sheep and hw they cpe with water scarcity. We als nte hw sme ther desert ungulates are adapted t water scarcity and cmpare the desert bighrn's capabilities t thse f ther species. Anatmical Adaptatins The desert bighrn lacks the bvius mdificatins f many desert mammals fr life in an arid envirnment. Fr example, light-clred cats reflect mre radiatin frm the sun r frm the grund than d darker-clred cats; many desert ungulates are very light-clred r even white. Cat clr f the desert bighrn, hwever, varies frm blackish t medium gray-brwn (Hansen 1980). The shape f desert bighrn extremities des nt represent typical desert adaptatin, nr des its general bdy cnfrmatin. Further, cmpared t successful ungulates f extreme desert habitats, the desert bighrn's internal structures, such as the kidney, are nt significantly mdified t cncentrate urine (Hrst 1971; Hrst and Lngwrthy 1971). Other internal structure adaptatins have nt been investigated in the desert bighrn. Anther adaptatin f many ungulates t arid, ht envirnments is the lack f fat reserves. Subcutaneus fat hinders the dissipatin f metablic heat and prbably evlved in respnse t cld envirnments and as a methd f string reserves. Even when in excellent cnditin, the Grant's gazelle (Gazella grand), ryx (Oryx gazella), and gerenuk (Litcranius wallen) have very little subcutaneus fat (Ledger et al. 1967); in cntrast, desert bighrns stre substantial amunts (Hansen 1980). Physilgical A adaptatins The ability t allw bdy temperature t rise a few degrees during the day withut panting and t lse that accumulated heat when the ambient temperatures drp at night is shared by many desert ungulates (Schmidt-Neilsen 1964; Taylr 1970,1972). Alternatively, sme animals decrease bdy temperatures during the night, a prcess which allws them t stre mre heat the next day. N studies n the desert bighrn have indicated that their bdy temperatures fluctuate significantly in relatin t ambient diel temperatures. Lwering the metablic rate minimizes heat prductin, and water fr cling is cnserved. This mechanism, als, is nt knwn t be used by the desert bighrn. The ability t extract water frm feces was reprted by Turner (1970) t be nearly as great in desert bighrns as in the camel (Camelus drmedarius). Turner als stated that desert bighrns btain little prefrmed water frm their fd and that metablic water prbably cntributes little t their verall water needs. Water ingested with fd cntributes t the verall intake f water, but during critical dry seasns, sme succulent plants may als be dehydrated. This means that the amunt f water required t vid the electrlytes btained frm the plants may exceed the amunt f water gained (Turner 1973; Turner and Weaver 1980).

12 Because neither the ability f desert bighrns t cncentrate urine nr their tlerance t ttal disslved slids in water is knwn, the questin f hw much prefrmed water they can btain frm drught-stressed plants remains unanswered. Behaviral Adaptatins During the early part f the dry seasn, pricklypear (Opuntia spp.), pincushin cactus (Mammillaria spp.), and barrel cactus (Echincactus spp.) may cntain enugh water t supplement free water ingested (Russ 1956; Simmns 1964; Krausman et al. 1985). Diet f desert bighrns in the Big Hatchet Muntains, NM, was 53% pricklypear in June, suggesting an increased cnsumptin f it as an adaptatin t a waterless range (Watts 1979). Turner (1973) cncluded that sheep did nt use freestanding water when frage cntained ml water/gram dry weight. On several ranges, bighrn sheep remain within km f permanent water surces (Grss 1960; Blng and Pllard 1968; Turner 1973). Kplin (1960) nted that bighrn sheep may migrate t higher elevatins and cler temperatures t reduce water lss frm evaprative cling. A male and female desert bighrn in Utah reduced their hme range size during summer mnths because f limited water availability (Wilsn 1971). Leslie (1977) fund that males frequented water sites mre ften during the breeding seasn. Campbell and Remingtn (1979) fund that 54% f the sheep in the Buckskin Muntain, AZ, range drank between dawn and 0800 h in June and 75% drank during that time in July. Kplin (1960) cncluded that a minimum f 82.5% f all drinking n the Desert Game Range (nw Desert Natinal Wildlife Range), NV, ccurs during daylight, with the greatest activity just befre sunrise (17.6%) and at 1200 h (19.7%). Turner and Weaver (1980) suggest that fr sheep t drink in early mrnings is energetically efficient behavir that reduces unnecessary heat gain. The frequency f drinking has been reprted by many authrs and has been assciated with seasn, temperature, days since last precipitatin, and frage misture. Drinking frequencies vary frm 1 t 5 d when temperatures are high and frage water is lw, t ttal independence f free water n sme ranges (Graves 1961; Welles and Welles 1961; Campbell and Remingtn 1979; Turner and Weaver 1980). The literature is replete with references t bighrn ppulatins that are able t survive withut freestanding water fr mnths r even thrughut the year. Mnsn (1958) bserved sheep that did nt drink water fr 6 m beginning 1 July n Cabeza Prieta Game Range (nw Natinal Wildlife Refuge), AZ. Valverde (1976) reprted that sheep n sme Snran ranges d nt drink. Krausman et al. (1985) mnitred tw radi-cllared ewes fr 10 d: During 239 h they did nt drink water, althugh the ambient temperature exceeded their presumed bdy temperature 33% f the time. In captivity, adult female and male desert bighrns cnsumed and L f water per day, respectively (Turner 1970, 1973; Kplin 1960). Turner and Weaver (1980) reprted that a grup f desert bighrns they bserved in the wild drank water in amunts f 20%-30% f the estimated bdy weights. Frm these bservatins and frm bservatins n penned animals, they estimated that desert bighrns must drink a minimum f 4% f bdy weight per day during the summer. Althugh water requirements f desert bighrns are nt cmpletely understd, they are apparently able t mdify their activities t cpe with envirnmental stresses. Unfrtunately, the paucity f basic water physilgy, metablic, and anatmical infrmatin leads t cnflicting cnclusins abut many aspects f desert bighrn eclgy. As a case in pint, a series f recent articles has discussed the pssibility that the desert bighrn is a relict frm mre mesic envirnments and is thus maladapted t desert habitats (Bailey 1980; McCutchen 1981; Hansen 1982; Wehausen 1984; Geist 1985). Authrs have develped arguments n bth sides f this issue, arguments which appear t be based n preliminary and perhaps inadequate studies. Management Recmmendatins Althugh much remains t be learned abut water requirements f desert bighrn sheep, general recmmendatins can be made t manage water quality and availability fr them. Water shuld be clean and distributed thrughut the ranges (every 3-5 km) such that a surce f water will be within the weekly area f activity f sheep. Water shuld be within 0.5 km f escape terrain with n dense, tall vegetatin in r arund the water, because sheep avid areas nt affrding ample visibility (Leslie and Duglas 1979; Hansen 1980; Turner and Weaver 1980). When water surces have t be created, they shuld be planned t decrease cnflict between desert bighrns, ther ungulates, and peple. By attracting ther ungulates t an area f limited resurces, adding water may increase cmpetitin, cause vergrazing, transfer parasites r disease between bighrns and native r dmestic ungulates (Bunch et al. 1978a), r cause fuling f water with feces (Welles and Welles 1961; Wilsn 1977). Krausman et al. (1985) and Krausman and Lepld (1986) expressed cncern ver the develpment f water in less than ptimal habitats where water has nt been demnstrated t be a limiting factr. Sheep may have existed n such ranges fr thusands f years withut free water and, althugh densities are lw, their number may be within the cnstraints f available resurces. Befre adding water in sheep habitat, the need fr water shuld be

13 established. If annual plant bimass has been measured and is adequate (suggesting that fd is nt a limiting factr), water shuld be supplied temprarily in mbile tanks befre building mre permanent water develpments. Research Recmmendatins The lack f answers t many basic questins abut the physilgy and anatmy f desert bighrns inhibits successful management. These answers are needed, but evaluatin f current and planned management techniques is necessary. We knw that when agencies prvide water t arid ranges, desert bighrn sheep use it; nevertheless, we need t study the effect f freestanding water n reprductin and survival t breeding age f bth sexes. The infrmatin n survival shuld be synthesized with results f studies n cmpetitin, disease, stress, and the effect f human disturbance. Sufficient infrmatin frm descriptive studies is available; nw, experimental research is justified and needed. Studies.that manipulate water availability and prvide measures f the management end prduct-mre r healthier desert bighrns-shuld be a pririty. Effects f Human Activity n Desert Bighrn Sheep Man's activity in bighrn sheep habitat has altered sheep behavir and ppulatins. Human disturbance at watering sites has created shifts in drinking behavir (Leslie and Duglas 1980; Campbell and Remingtn 1979) which may affect lamb survival (Leslie and Duglas 1980). Vehicle use and related human activity has reduced sheep use f areas arund water by 50% (Jrgensen 1974). The recreatinal demands n bighrn sheep habitat include picnicking, camping, explring, hiking, hunting, rck-hunding, and desert dwelling, any f which can destry bighrn sheep cver and water. Hw sheep respnd t these pressures varies (Nelsn 1966). DeFrge (1972) demnstrated that rad traffic can negatively influence sheep ppulatins, but recreatinal use f trails is nt necessarily detrimental (Hicks and Elder 1979; Hamiltn et al. 1982). Purdy and Shaw (1981) reprted that sheep are nt influenced by mst hiking activity, but sme activities (hunting, hiking and camping, vehicle traffic) may nt be cmpatible with sheep. Sme f man's uses f sheep habitat-mining, paching, hunting, ranching, fence cnstructin, and urbanizatin-are detrimental t sheep (Duncan 1960; Fllws 1969; Helvie 1971; Ferrier 1974; Krausman et al! 1979; Ginfridd and Krausman 1986). Cmbinatins f these activities may cause sheep t restrict their use f quality habitat r t frm smaller grups resulting in fewer sheep per unit f habitat. Human-sheep interactins are difficult t evaluate because man's activities in sheep habitat are s varied. Hw an individual disturbs ne r mre sheep is a cmplex questin-the disturbance may be planned r impulsive, intentinal r unintentinal, purpseful r irratinal, bvius r barely nticeable. Anyne is capable f disturbing sheep at any time, and the results maybe insignificant r catastrphic. It is imprtant that managers f sheep habitat and ppulatins be able t identify ptential prblems and efficiently eliminate them. Fr example, if critical habitats at certain seasns are suspected f being influenced by man, the public shuld be infrmed f the prblem and entry t the areas restricted. Althugh peple can be detrimental t bighrn sheep ppulatins unintentinally, an infrmed public may be the slutin t sme human-sheep interactin prblems. Examples f Management Restrictins Limited Access t Kfa Bighrn sheep exist n ranges tday because f management decisins. If their survival is imprtant, but impaired by man's activity, human activities will have t be restricted. The success f the bighrn sheep prgram n the Kfa Natinal Wildlife Refuge, perated by the U.S. Fish and Wildlife Service in western Arizna, is a direct result f setting pririties fr the success f the sheep ppulatin. Access t the range is limited, and sheep are prtected frm habitat alteratin. Sheep frm this ppulatin have been transplanted thrughut the suthwestern United States, and the hunting pprtunities n the Refuge are f the highest quality. Santa Catalina Muntains and Dg Cntrl Geist (1975) argued that ptentially cnsumptive and nncnsumptive uses f sheep can be detrimental t any given ppulatin f sheep. Results can be disastrus if develpment is added, as exemplified by the sheep ppulatin in the Santa Catalina Muntains utside f Tucsn, AZ. The city has grwn t brder the western and suthern edges f sheep habitat n the Pusch Ridge Wilderness (suthwestern crner f the Santa Catalina Muntains in the Crnad Natinal Frest). As parks, business parks, husing develpments, htels, and recreatinal trails cntinue t be develped n the edge f and int sheep habitat, the future f sheep n the range becmes prblematic. There are very few, if any, restrictins n human use f this sheep habitat, and residents f Tucsn use the muntain fr numerus recreatinal activities. In the early 1980's, the Pusch Ridge Wilderness received mre than 34,000 recreatinal visitrs annually (Purdy and Shaw 1981). This number will undubtedly increase as Tucsn cntinues t grw, but it is nt clear if the increased number inundating sheep habitat will be

14 cntrlled. Survey respndents, faced with a hypthetically declining sheep ppulatin in this habitat, favred mandatry restrictins n recreatinal use in specified areas during critical seasns (Purdy and Shaw 1981). Hwever, it is never certain whether such restrictins, if implemented, wuld be heeded. Hicks and Elder (1979) reprted that 66% f 35 grups f hikers they interviewed in Califrnia's Sierra Nevada Muntains stated they had engaged in sme frm f prhibited ff-trail activity. In the Pusch Ridge Wilderness, where nly 8% f thse surveyed have claimed ever t have seen sheep (Purdy and Shaw 1981), it may be difficult t cnvince recreatinists f the need t impse and bey use restrictins. One such negative example exists: The U.S. Frest Service has tried in vain t enfrce leash restrictins fr pets in this area since On 11 August 1986, bighrn sheep habitat in the Pusch Ridge Wilderness was effectively clsed t dgs by Federal regulatin dgs n leashes were allwed n the trails frming the perimeter f the clsed area, but the heart f the bighrn habitat was declared ff-limits t dgs. Vilatins f the restrictin are punishable by a fine f nt mre than $500 r imprisnment fr nt mre than 6 m r bth, but cmpliance has been lw and the regulatins thus ineffective. It may prve impssible t implement and enfrce ther restrictins necessary t prtect the remaining sheep n the Wilderness. Unfrtunately, the Pusch Ridge Wilderness ppulatin f bighrn sheep will thus face a critical test f its ability t withstand human encrachment. Althugh sme sheep may becme habituated t cmmn human-related stimuli (Hicks and Elder 1979), thers may temprarily r permanently abandn areas frequented by man (Dunaway 1971; Campbell and Remingtn 1979). Unfrtunately, all indicatins are that this ppulatin will respnd negatively t man's develpment unless rigid restrictins n access and use are made and strictly enfrced. Management Recmmendatins Managers shuld be aware f human activities that have caused a direct decline f sheep elsewhere and shuld be familiar with specific cnditins in sheep ranges under their management that may result in human-sheep cnflict. These cnflicts can be identified and reslved by lng-term mnitring and apprpriate management actins. These actins largely invlve restrictin f the quantity, type, and timing f human activity n sheep range. Whenever restrictins are impsed, it is imprtant that the ppulatin affected be infrmed why restrictins are necessary. Laws are nly enfrceable if they are respected by bth the public and enfrcement persnnel. Infrmatin n hw man's recreatinal pursuits influence bighrn sheep is limited. Whenever man and bighrn sheep regularly share the same range, every effrt shuld be made t determine hw human activity affects the bighrn sheep ppulatin. Management's best respnse is t be cnstantly aware f actual r ptential detrimental human activities. Disease and its Cntrl Desert bighrn sheep are susceptible t many diseases and parasites. Bacterial pneumnia (Pasteurella spp., Staphylcccus spp., Crynebacterium spp.), chrnic sinusitis, para-influenza-3, bluetngue, epiztic hemrrhagic disease, and cntagius ecthyma are amng diseases that afflict desert bighrns (Hailey et al. 1972; Bunch 1979; De Frge et al. 1981; Allen and Bunch 1982; Turner and Paysn 1982). Imprtant parasites include lungwrms, Prtstrngylus stilesi (Allen 1971) and Muellerius capillaris (Russi and Mnre 1976); scabies mites, Psrptes cervinus and P. vis (Cater 1968; Decker 1970; Bunch et al. 1978a,b,c; de Vs et al. 1980); and the bt fly, Oestrus vis (Bunch et al. 1978a,b). Numerus tapewrms, nematdes, ticks, and fleas als infest desert bighrns but are less debilitating than the ther parasites mentined. Indirectly, ectparasites may be imprtant vectrs fr disease-causing rganisms. Allen (1980) summarized diseases and parasites and their relative imprtance t desert bighrns, and Krausman et al. (1984) updated the literature n this subject in their anntated bibligraphy. Diseases f any wild ppulatin are difficult t treat. Cnsequently, the twfld gal f management shuld be preventin f cnditins that prmte dangerus diseases and early detectin f diseases. Once a serius disease is firmly established, nly herculean effrts may prevent substantial lsses. In this sectin, we discuss prcedures t cntrl disease in desert bighrn sheep, suggest prphylaxis r treatment, and identify research needs. A Perspective fr Disease Evaluatin Disease rganisms may nrmally be present in the envirnment f a bighrn sheep ppulatin but cause little damage if the animals are in gd physical cnditin. Inadequate frage quantity r quality, inclement weather, expsure t livestck, and ther stressful events can predispse individual sheep t disease (Allen 1980). Geist (1985) suggested that the small size f desert bighrns may be evidence that they are suffering chrnic shrtages f nutrients. Evans (1978) emphasized that fr dmestic animals, maintaining health is a psitive apprach and is mre efficient than merely preventing disease-this statement culd als apply t wild animals. Diseases t which bighrns have nt previusly been expsed may spread rapidly thrugh a ppulatin-dmestic r feral animals may intrduce extic diseases r parasites; wild animals that extend

15 their range because f natural r man-induced envirnmental change may intrduce diseases t which bighrns have nt acquired immunity; intrducing desert bighrn sheep int areas where ther ungulates exist may subject the sheep t diseases t which they are nt immune. Althugh current indicatins are that this latter prblem remains nly a ptential threat t desert bighrns, examples f this situatin fr ther species are numerus, including the transfer f arterial wrms (Elaephra schneiden) frm deer t elk (Hibler and Adcck 1971; Wrley 1975) and meningeal wrms (Pneumstrngylus tenuis) frm white-tailed deer (Odcileus virginianus) t ther Nrth American cervids (Eckrade et al. 1970; Prestwd 1970). Scabies Recent Disease Prblems In 1978, five rams sht in the San Andres Natinal Wildlife Refuge were nted t have psrptic mites and scabies lesins. The next year, the number f sheep bserved n surveys drpped by mre than 60% frm 200 t 70. Scabies was the suspected cause, even thugh n deaths attributable t scabies were dcumented (Lange et al. 1980; Sandval 1980). The effects were already serius by the time the disease was discvered in the ppulatin. Prmpt actin t capture, enclse, and treat the remaining individuals saved a prtin f the ppulatin. Frty-nine sheep were captured and dipped in a txaphene slutin; 34 sheep survived. Of the estimated sheep remaining n the range, 19 were injected with ivermectin by way f a ballistic implant sht frm a cmpressed-air rifle (Sandval 1980). Althugh the ballistic implant still hlds prmise, it was unsuccessful in applicatin, because absrptin was hindered by a tissue reactin t the drug-carrying matrix, and because tw dses f the dilute cncentratin f the drug were required. Twelve f the sheep mved after the mite utbreak were reintrduced in 1981 (Munz 1981). These 12, and 13 f the remnant ppulatin, were radi-cllared t track mvements and mnitr mrtality (Munz 1982). Even thugh Munz (1982) saw n indicatin f scabies during 1981, Kinzer et al. (1983) reprted that scabies infectins cntinued in Frm 1981 t 1983, sheep that were captured were injected with invermectin with hand syringes. During 1984 captures, 18 sheep had clinical symptms, and 8 had mites. In 1985,7 f 14 captured sheep had clinical symptms and all had mites (A. Sandval, persnal cmmunicatin). The unslved questin remains has an especially virulent strain f Psrptes vis evlved, r is this ppulatin especially susceptible t this parasite? Desert Bighrn Chrnic Sinusitis Desert bighrn chrnic sinusitis (DBCS) is thught t be caused by the bt fly which induces a bacterial infectin within the frntal and crnual sinuses. Apparently, the larvae are depsited in the nasal passage and infect the hst with a bacterium. DBCS is a serius mrtality factr (Bunch et al. 1978a,b,c). Bunch and Webb (1979) examined 69 skulls and fund 45% f the ewes and 22% f the rams had been infected. They thught that these figures were cnservative estimates, because at Zin Natinal Park, Utah, nly 50% f the sheep that had DBCS actually exhibited skeletal lesins. Eight f 16 skulls that we examined frm 1979 t 1986 frm the Harquahala cmplex in Arizna had lesins, suggesting that this disease may be as serius a threat t bighrn sheep as Bunch et al. (1978c) indicated. As an additinal cmplicatin, Bunch and Allen (1981) reprted that 20% f 630 bighrn skulls had bne anmalies that they believed were caused by pygenic stemyelitis. Bunch (1979) pstulated that pygenic stemyelitis was evidence f chrnic sinusitis and thught that nearly all ppulatins surveyed in Arizna were affected. The infectin in this disease is usually in the crnual sinus area. After an abscess frms ver the brain case, the disease penetrates t the brain and eventually kills the animal. In captive animals, the disease is difficult t detect early in its curse; early detectin in wild animals is even mre difficult. Management Recmmendatins Preventin f disease may best be accmplished by maintaining a healthy ecsystem. This requires that range cnditins be as gd as pssible. Minimizing stresses frm vercrwding, pr nutritin, drught, cmpetitin frm ther ungulates (native r intrduced), harassment by humans during critical perids, and bisectin r fragmentatin f habitat prvides a psitive apprach t disease cntrl. This requires that mnitring f habitat variables be a pririty. Detailed and systematic recrds n ppulatin size, cmpsitin, reprductin, and physical cnditin f desert bighrns as well as ther ungulates shuld be btained. Whenever pprtunities t handle live r freshly-killed animals arise, maximum amunts f infrmatin shuld be gathered. Animals captured, fr whatever purpse, shuld be examined; prper samples shuld be taken, and the material analyzed by trained persnnel. Wehausen (1987) cautins that when a ppulatin is sampled fr the presence r absence f a disease, nly presence can be shwn cnfidently. In rder t state with cnfidence that prevalence f any disease in a ppulatin is 10% r less, prhibitively large sampling is necessary. If desert bighrns are t be managed prperly, every attempt shuld be made t anticipate prblems rather than react t crises after they ccur. Appendixes A and B cntain infrmatin n techniques fr cllecting

16 samples and gathering apprpriate data as suggested in this sectin. Research Recmmendatins In additin t nging mnitring f the health f wildlife ppulatins, there are sme basic questins that require answers. Why are certain ppulatins peridically infected with scabies and ther ppulatins rarely infected? Are the apparent immunities caused by genetic differences r previus expsure, r are disease rganisms mre virulent in varius areas? Are reintrduced sheep being subjected t a set f ptential diseases t which they have had n previus expsure and, therefre, n acquired immunity? What diseases r vectrs f disease rganisms are maintained r spread by ther native wildlife that are in cntact with bighrn sheep? Are there ways t segregate varius species f animals at water hles t minimize cntact with the disease rganisms they harbr? Wuld it be pssible t cntrl the incidence f bt fly-caused chrnic sinusitis by using pesticides, releasing sterilized male flies int prblem areas, r ther bilgical cntrls? Culd water hle cnstructin be used t disperse cncentratins f animals, thereby minimizing ptential fr cntaminatin? Is water at cncentratin areas a surce f infectin, and culd the water be treated? Is disease merely an indicatr f unhealthy cnditins induced by ther causes? T answer these questins, wildlife bilgists shuld cllabrate with scientists in ther disciplines. Veterinarians, pathlgists, entmlgists, parasitlgists, and eclgists are required t establish an effective team t prvide answers. Releasing desert bighrn sheep nt unccupied ranges, develping water surces, and altering f habitats are management activities that may alter the dynamic equilibrium between desert bighrn sheep and disease rganisms. Cnsequently, research int the relatin f disease and parasites t these activities shuld have pririty. Interspecific Relatins Ppulatin dynamics f bighrn sheep can be affected by resident species f big and small game thrugh cmpetitin, predatin, and the transmissin f diseases and parasites. Varius relatins exist between bighrn sheep and ther species inhabiting a prtin r all f the same range. Hwever, literature frm the Suthwest indicates that, under usual cnditins, bighrn sheep are nt adversely affected by ther wildlife species. Cmpetitin Game species which may be pssible cmpetitrs f the desert bighrn include mule deer, cllared peccary (Tayassu tajacu), black-tailed jack rabbits (Lepus califmicus), white-winged dves (Zenaida asiatka), Gambel's quail (Callipepla gambelii), and chukars (Alectris chukar). Cmpetitin between these species and bighrn sheep is mainly crrelated with restricted water availability. Jnes (1980) stated that mule deer and bighrn sheep habitats verlap at watering places, and where water is limited, cmpetitin may exist. On sheep range in the Desert Natinal Wildlife Range, Nevada, cmpetitin was dcumented between sheep and mule deer (Jnez 1960). Hallran and Deming (1958) nte that mule deer may be respnsible fr depleting water n many suthwestern ranges. White-winged dves, Gambel's quail, and chukars have been reprted t cnsume water t the detriment f sheep (Jnes 1980; Welles 1965). Cmpetitin between bighrn sheep and mule deer fr frage may als exist; Jnes (1954) stated that where terrain is nt rugged, sheep may be frced t cmpete with deer fr frage. Direct cmpetitin fr key brwse species may ccur, especially during winter (Kennedy 1963). Hwever, analysis f sheep and deer feces indicates that the diet differences (sheep-65% grass species; deer 77% brwse species) are enugh t prevent direct cmpetitin (Yakum 1966). Buechner (1960) warned that the effect deer have n sheep numbers may be greater than verlapping diets indicate. Overlap between deer and sheep hme ranges may cause vegetatin t deterirate, causing sheep, rather than deer, t decline because f the lw reprductive rate f sheep. Other wildlife als interact with desert sheep. Russ (1956) bserved the presence f cllared peccary n many sheep ranges but indicated that the extent f interspecific cmpetitin was unknwn. Jnes (1980) stated that diets f sheep and black-tailed jack rabbits verlap, but cmpetitin has nt been dcumented between them. Dmestic and intrduced species have a greater cmpetitive effect n sheep than d resident species. The negative effects f Barbary sheep (Ammtragus lervia); wild burrs; and dmestic cattle (Bs taurus), sheep (Ovis aries), and gats (Capra hircus) n desert bighrns is well dcumented (Simpsn et al. 1978). Barrett (1967) nted the ptential threat f Barbary sheep t bighrn sheep, resulting frm similar habitat and diet preferences. Lee (1960) suggested the pssibility f transmissin f disease and parasites t bighrn sheep by Barbary sheep. Seegmiller and Simpsn (1979) warned that intrduced Barbary sheep might cmpete with bighrn sheep and ther members f the natural ecsystem. Burrs in bighrn sheep range create similar prblems. Burrs damaged sheep habitat in the Lwer Clrad River Valley in Arizna and Califrnia (Hanley and Brady 1977) and in the Panamint Muntains, CA (Duglas and Nrment 1977). 8

17 McMichael (1964) determined that an verlap between burrs and bighrn sheep exists in frage cnsumptin and summer ranges in the Black Muntains in Arizna. Seegmiller and Ohmart (1981) discussed the verlap f diet and habitat preferences between bighrn sheep and burrs. Dunn and Duglas (1982) dcumented the decreased usage f watering surces by bighrn sheep when high numbers f burrs are present in Death Valley Natinal Mnument, CA. Weaver (1959, 1973) discussed the effect burrs have n the watering surces f bighrn sheep. The impact f dmestic cattle, sheep, and gats n native ppulatins f bighrn sheep is discussed by Jnes (1980) and Gallizili (1977). Predatin Predatin in the Suthwest n bighrn sheep is cmmn. Hwever, it is nt cnsidered a serius threat t any ppulatin f bighrn sheep, and mst predatin is pprtunistic (Kelly 1980). Predatrs f desert bighrn sheep include cyte, gray fx, bbcat, and muntain lin (Gldman 1961). Weaver (1961) stated that the cyte is the mst cmmn predatr n sheep ranges, but that it is relatively unimprtant in the ppulatin dynamics f bighrn sheep. McQuivey (1978) bserved cytes chasing and feeding upn sheep n several ccasins. Simmns (1969) recrded 12 cyte interactins with sheep, nting that sheep seem t be mst vulnerable arund watering hles. Analysis f cyte scat indicates that sheep and deer ccur relatively infrequently in cyte diets (Russ 1956; Simmns 1969). Predatin by gray fx n sheep has been reprted in the Plmsa and Mhawk muntains, Arizna (Nichl 1937). Hwever, the actual effectiveness and frequency f predatin by gray fx is unknwn. Bbcat predatin and cnsumptin f bighrn sheep has been dcumented in the Suthwest (Russ 1956; Grves 1957; Ellit 1961), but bbcats d nt seriusly threaten the ppulatins f bighrn sheep in the Suthwest. The muntain lin des nt influence mst sheep ppulatins. Only small ppulatins f muntain lins exist n established desert bighrn sheep ranges and have nt been dcumented as a significant cause f mrtality (Kelly 1980). Many single bservatins f muntain lin predatin are recrded (Carsn 1941; Gabrielsn 1941; Crnemiller 1948; Cain et al. 1972). Management Recmmendatins Mst studies that have evaluated interspecific relatins between bighrn sheep and native wildlife have cncluded that the relatins are nt detrimental t sheep. Hwever, larger ungulates such as desert mule deer may seriusly cmpete fr frage and water. Managers shuld be aware that placing water in bighrn sheep habitat may als attract deer which culd directly cmpete with sheep. Having evlved tgether, native wildlife species are usually cmpatible, but intrduced animals and dmestic livestck create serius prblems. Usually, whenever burrs and livestck share range with desert bighrns, prblems develp: native sheep are eventually eliminated thrugh diseases transmitted by dmestic stck r cmpetitin by burrs and extic species. Managers shuld nt allw livestck, extics, r burrs n desert bighrn sheep ranges. Under nrmal circumstances, cexistence is nt pssible. If ther species are already present, the nly slutin that favrs desert bighrns is t remve the ther animals. Research Recmmendatins Mre infrmatin is needed n the relatins between deer and desert bighrn sheep in natural and altered habitats. Jnes (1980) and Hallran and Deming (1958) suggested that deer may successfully cmpete with bighrns fr frage and water but specific data are lacking. In sme ranges such as the Santa Catalina Muntains in Arizna, fire has been recmmended as a tl t create bighrn habitat; hwever, interactins between sheep and deer n burns have nt been dcumented. Research f interspecific interactins n altered habitats (e.g., burns, waterhles) wuld be valuable. Because the influence f predatrs, particularly muntain lins, n sheep ppulatins in suthern ranges is limited, little remedial actin seems necessary. Hwever, managers shuld be alert fr prblems that may develp when sheep ppulatins are lw, the range is in pr cnditin, r water supplies are extremely limited. Diseases and parasites f species nt sharing range with bighrn sheep pse little threat, even thugh bighrns may be susceptible. When barriers are remved by habitat changes, and ppulatins mix r extic species are intrduced, there is ptential fr great harm. Any study f sympatric ungulates shuld include investigatins f their diseases and parasites. Synpsis Many bilgists have studied desert bighrn sheep, and there is a wealth f literature available n their life histry, behavir, and management. The desert bighrn apparently is nt adapted physically r physilgically t a desert envirnment t the extreme extent f many ther desert ungulates. Thus, there is need fr mre cmplete physilgical and anatmical descriptins f the mechanisms f temperature regulatin and water retentin that permit this species t use arid habitat. The desert bighrn apparently adapts behavirally t the extremes f heat and water shrtage, but mre shuld be learned f this behavir t guide management. Man's activities are increasing the pressure n desert bighrn ppulatins. The cmbined effects f habitat fragmentatin, degradatin, and alteratin added t cmpetitin frm ther ungulates will cntinue t stress