Animal Diversity Web

Ge­o­graphic Range

Odocoileus hemionus oc­curs over most of North Amer­ica west of the 100th merid­ian from 23 de­grees to 60 de­grees N. The east­ern edge of the usual range ex­tends from south­west­ern Saskatchewan through cen­tral North and South Dakota, Ne­braska, Kansas, and west­ern Texas. Iso­lated oc­cur­rences have been re­ported from Min­nesota, Iowa, and Mis­souri. Major gaps in ge­o­graphic dis­tri­b­u­tion are in south­ern Nevada, south­east­ern Cal­i­for­nia, south­west­ern Ari­zona, and the Great Salt Lake desert re­gion. Apart from these gaps, O. hemionus oc­curs in all of the bio­mes of west­ern North Amer­ica north of cen­tral Mex­ico, ex­cept the Arc­tic tun­dra (An­der­son 1984).

• Biogeographic Regions
• nearctic
  • native

Habi­tat

Odocoileus hemionus is re­mark­ably adapt­able. Of at least sixty types of nat­ural veg­e­ta­tion west of the 100th merid­ian in the United States, all but two or three are or once were oc­cu­pied by O. hemionus. Sev­eral ad­di­tional veg­e­ta­tion types are in­hab­ited in Canada and Mex­ico as well. The veg­e­ta­tion types in Mex­ico are sim­i­lar to the types oc­cur­ring in the United States. How­ever, the trop­i­cal de­cid­u­ous veg­e­ta­tion at the tip of Baja Cal­i­for­nia is unique. In Canada, O. hemionus oc­cu­pies five bo­real for­est types that do not occur in the United States. O. hemionus oc­cu­pies a wide range of habi­tat provinces (re­gions of land con­tain­ing par­tic­u­lar veg­e­ta­tion types) in west­ern North Amer­ica. These habi­tat provinces in­clude the Cal­i­for­nia wood­land chap­ar­ral, the Mo­jave Sono­ran desert, the In­te­rior semi­desert shrub wood­land, the Great Plains, the Col­orado Plateau shrub­land and for­est, the Great Basin, the Sage­brush steepe, the North­ern moun­tain, and the Cana­dian bo­real for­est (Wallmo 1981).

• Terrestrial Biomes
• desert or dune
• savanna or grassland
• chaparral
• forest
• mountains

Phys­i­cal De­scrip­tion

The pelage of Odocoileus hemionus ranges from dark brown gray, dark and light ash-gray to brown and even red­dish. The rump patch may be white or yel­low, while the throat patch is white (Geist 1981). The white tails of most mule deer ter­mi­nate in a tuft of black hairs, or less com­monly in a thin tuft of white hairs. On some mule deer, a dark dor­sal line runs from the back, down the top of the tail, to the black tail tip. All mark­ings vary con­sid­er­ably among O. hemionus, but re­main con­stant through­out the life of an in­di­vid­ual. O. hemionus pos­sess a dark V-shaped mark, ex­tend­ing from a point be­tween the eyes up­ward and lat­er­ally. This mark is more con­spic­u­ous in males. Growth in O. hemionus dur­ing the first year is roughly par­al­lel in males and fe­males. There­after, males, in gen­eral, ex­ceed fe­males in car­cass weight, chest girth, neck cir­cum­fer­ence, body length, head length, cra­nial breadth, shoul­der height, hind­foot length, and hoof length (An­der­son 1984). Car­cass weight ranges from 45 to 150 kg in males, and 43 to 75 kg in fe­males. Chest girth ranges from 80 to 117 cm in males, and 78 to 97 cm in fe­males. Neck cir­cum­fer­ence ranges from 30 to 65 cm in males, and 26 to 38 cm in fe­males. Body length ranges from 126 to 168 cm in males, and 125 to 156 cm in fe­males. Head length ranges from 28 to 35 cm in males, and 27 to 33 cm in fe­males. Cra­nial breadth ranges from 11 to 16 cm in males, and 10 to 14 cm in fe­males. Shoul­der height ranges from 84 to 106 cm in males, and 80 to 100 cm in fe­males (Wallmo 1981).

• Other Physical Features
• endothermic
• bilateral symmetry

• Range mass

  43 to 150 kg

  94.71 to 330.40 lb

Re­pro­duc­tion

Odocoileus hemionus is a polyg­y­nous species, hav­ing a tend­ing-bond type breed­ing sys­tem. Courtship and mat­ing occur within the group (Geist 1981). A dom­i­nant male tends an es­trus fe­male until mat­ing or dis­place­ment by an­other male oc­curs. Dom­i­nance is largely a func­tion of size, with the largest males, which pos­sess the largest antlers, per­form­ing most of the cop­u­la­tions (Kucera 1978). Most O. hemionus fe­males con­ceive dur­ing their sec­ond year and only rarely dur­ing their first year. The breed­ing peak in O. hemionus oc­curs mainly from late No­vem­ber through mid-De­cem­ber. The av­er­age ges­ta­tion length is 204 days. The peak birth pe­riod in O. hemionus is es­ti­mated to be from June 16th to July 6th, with most births oc­cur­ring in June. The time of birth varies ac­cord­ing to the en­vi­ron­ment. Robi­nette (1977) cal­cu­lated that a 305-m rise in el­e­va­tion is as­so­ci­ated with a 7-day delay in the birth pe­riod. The mass at birth of O. hemionus ranges from 2 to 5 kg. Mass at birth is af­fected by lit­ter size and sex, with males being heav­ier. The com­mon liter size is two, with moth­ers in their first or sec­ond breed­ing year most fre­quently pro­duc­ing sin­gle­tons. Wean­ing be­gins at about 5 weeks of age and usu­ally is com­pleted at age 16 weeks. Full de­vel­op­ment of most skele­tal at­trib­utes oc­curs at about 49 months of age in males and 37 months of age in fe­males. How­ever, gains in car­cass mass are con­tin­u­ous until an age of 120 months in males and 96 months in fe­males. In O. hemionus, male neonates pre­dom­i­nate when poor nu­tri­tion pre­vails about 6 weeks be­fore, and dur­ing, the breed­ing pe­riod. Ovu­la­tion in fe­male O. hemionus oc­curs about 12 to 14 hours after es­trus ter­mi­nates. Ap­prox­i­mately 27 to 29 days elapse be­tween con­cep­tion and im­plan­ta­tion in fe­male O. hemionus. Among male O. hemionus, tes­tic­u­lar mass and vol­ume are max­i­mal dur­ing No­vem­ber and min­i­mal dur­ing April and May (An­der­son 1984).

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual

• Average number of offspring

  1.5

  AnAge

• Average gestation period

  207 days

  AnAge

• Average age at sexual or reproductive maturity (female)
  Sex: female

  478 days

  AnAge

• Average age at sexual or reproductive maturity (male)
  Sex: male

  503 days

  AnAge

Lifes­pan/Longevity

• Average lifespan
  Status: captivity

  22 years

  AnAge

Be­hav­ior

In­di­vid­u­als of Odocoileus hemionus tend to con­fine their daily move­ments to dis­crete home ranges. Most mule deer with es­tab­lished home ranges use the same win­ter and sum­mer home ranges in con­sec­u­tive years. Dis­per­sal in O. hemionus in­volves move­ments be­yond the home range to dis­tances of up to 8 km. This move­ment re­sults in the es­tab­lish­ment of a new home range. Sea­sonal move­ments in­volv­ing mi­gra­tions from higher el­e­va­tions (sum­mer ranges) to lower win­ter ranges are as­so­ci­ated, in part, with de­creas­ing tem­per­a­tures, se­vere snow­storms, and snow depths that re­duce mo­bil­ity and food sup­ply. Deep snows ul­ti­mately limit use­able range to a frac­tion of the total. Mule deer in the arid south­west may mi­grate in re­sponse to rain­fall pat­terns. Com­mon preda­tors of O. hemionus in­clude pumas, coy­otes, bob­cats, golden ea­gles, feral dogs, and black bears. The so­cial sys­tem of O. hemionus con­sists of clans of fe­males re­lated by ma­ter­nal de­scent. These clans are the fac­ul­ta­tive re­source de­fend­ers. Males dis­perse as in­di­vid­u­als or ag­gre­gate in groups of un­re­lated in­di­vid­u­als. Dur­ing win­ter and spring, the sta­bil­ity of fe­male clans and male groups is main­tained with dom­i­nance hi­er­ar­chies. In­creases in strife and alarm be­hav­ior, and de­creases in play among fawns, occur as pop­u­la­tion den­sity in­creases. The fre­quency of ag­gres­sive be­hav­ior be­tween the sexes re­mains low year round in O. hemionus. Com­mu­ni­ca­tion among O. hemionus is fa­cil­i­tated by the se­ba­ceous and su­dorif­er­ous se­cre­tory cells of five in­tegu­men­tary glands. The cells of each gland pro­duce spe­cific scents (pheromones) that elicit spe­cific re­ac­tions in con­specifics. The metatarsal gland pro­duces an alarm pheromone, the tarsal gland aids in mu­tual recog­ni­tion, the in­ter­dig­i­tal gland leaves a scent trail, and the func­tion of the tail gland is un­known. Urine has a pheromone func­tion at all ages and for both sexes. It is de­posited on tufts of hair sur­round­ing the tarsal glands. In fawns, it func­tions as a dis­tress sig­nal, while in adults, it func­tions as a threat sig­nal (An­der­son 1984). O. hemionus has sev­eral dis­tinct strate­gies for avoid­ing preda­tors. O. hemionus spe­cial­izes in de­tect­ing dan­ger at a very long range by means of large ears and ex­cel­lent vi­sion. Males can quickly de­tect and vi­su­ally track an­other an­i­mal as far as 600 me­ters. Once dan­ger is de­tected, O. hemionus may choose to hide, or move into cover and cau­tiously out­ma­neu­ver the preda­tor. An­other strat­egy is to de­part while the preda­tor is still a long way off and move sev­eral miles to an­other area. O. hemionus, in­stead, may bound rapidly up­hill, im­pos­ing on pur­su­ing preda­tors an un­ac­cept­ably high cost per unit time of lo­co­mo­tion. In yet an­other strat­egy, O. hemionus may bound off and then trot away, stop­ping fre­quently to gain in­for­ma­tion on the dis­tur­bance. This ini­tial bound­ing, com­bined with re­lease of metatarsal scent that in­hibits feed­ing, is highly ad­van­ta­geous in that, by alarm­ing oth­ers, it causes other mule deer to bound off as well, re­duc­ing the con­spic­u­ous­ness of the deer who bounded off first. This strat­egy would also trig­ger group for­ma­tion. Fi­nally, when a preda­tor closes in, O. hemionus ini­ti­ates eva­sive ma­neu­vers based on sud­den un­pre­dictable changes in di­rec­tion and on plac­ing ob­sta­cles be­tween it­self and the preda­tor. This strat­egy, how­ever, does not work against group-hunt­ing preda­tors. O. hemionus is an ex­cel­lent swim­mer, but water is rarely used as a means of es­cap­ing preda­tors (Geist).

• Key Behaviors
• motile
• social

Com­mu­ni­ca­tion and Per­cep­tion

• Perception Channels
• tactile
• chemical

Food Habits

Odocoileus hemionus is a small ru­mi­nant with lim­ited abil­ity to di­gest highly fi­brous roughage (Short 1981). Op­ti­mum growth and pro­duc­tiv­ity of in­di­vid­u­als and pop­u­la­tions are de­pen­dent upon ad­e­quate sup­plies of highly di­gestible, suc­cu­lent for­age. Diets con­sist­ing pri­mar­ily of woody twigs can­not meet the main­te­nance re­quire­ments of O. hemionus. Based on its stom­ach struc­ture and its diet of woody and herba­ceous for­age in ap­prox­i­mate equal pro­por­tions, O. hemionus is clas­si­fied as an in­ter­me­di­ate feeder. Be­cause nu­tri­tious for­age is in poor sup­ply for much of the year, O hemionus has an an­nual cycle of meta­bolic rates. A higher en­ergy flux and food in­take in the sum­mer en­ables O. hemionus to cap­i­tal­ize on abun­dant high-qual­ity for­age for growth and fat stor­age. A lower en­ergy flux in the win­ter per­mits O. hemionus to sur­vive on a lower in­take of poor-qual­ity for­age while min­i­miz­ing the ca­tab­o­lism of stored fat for body func­tions. The es­ti­mated rate of food in­take is about 22 g/kg body weight/day. In adult males, food in­take drops abruptly with the onset of rut (An­der­son 1984). O. hemionus fre­quently browses leaves and twigs of trees and shrubs. Green leaves are very suc­cu­lent and, ex­cept for epi­der­mal tis­sue and struc­tural ribs, con­sist largely of eas­ily di­gestible cell con­tents. Dead and weath­ered leaves have lit­tle pro­tein and high cell-wall val­ues. As a re­sult, they are of very low di­gestibil­ity. O. hemionus also eats acorns, legume seeds, and fleshy fruits, in­clud­ing berries and dru­pes, that have mod­er­ate cell-wall lev­els and are eas­ily di­gested (Short 1981).

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Odocoileus hemionus is of tremen­dous in­ter­est to hunters. Pop­u­la­tions of O. hemionus that are large enough to sup­port hunt­ing dur­ing two or three weeks in au­tumn offer count­less recre­ational op­por­tu­ni­ties for the pub­lic. This de­sire to hunt gen­er­ates rev­enue for the econ­omy (Wallmo 1981).

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Dou­glas fir and Pon­derosa pine are of major eco­nomic im­por­tance for com­mer­cial tim­ber. How­ever, these trees are browsed heav­ily by O. hemionus. Brows­ing of other trees is sel­dom con­sid­ered an eco­nomic prob­lem. In the Dou­glas fir re­gion, O. hemionus browses on trees dur­ing both the dor­mant and grow­ing sea­sons. Prac­tices that en­cour­age the growth of O. hemionus pop­u­la­tions can there­fore also en­cour­age dam­age. Dou­glas fir is har­vested mainly by clearcut­ting and is re­gen­er­ated by plant­ing with nurs­ery-grown stock. O. hemionus is at­tracted to clear-cuts, and Dou­glas fir is an ac­cept­able and some­times pre­ferred for­age species. This sit­u­a­tion in­vites brows­ing of suf­fi­cient in­ten­sity to in­flu­ence for­est re­gen­er­a­tion in many areas (Wallmo 1981).

Con­ser­va­tion Sta­tus

All fed­eral, state, and provin­cial land and wildlife man­age­ment agen­cies rec­og­nize the fun­da­men­tal need to main­tain O. hemionus ranges and keep them hab­it­able. To counter the trend of agri­cul­tural de­vel­op­ment, range­land con­ver­sion, min­ing, road and high­way con­struc­tion, and the de­vel­op­ment of hous­ing tracts, many states and provinces have pur­chased crit­i­cal areas, es­pe­cially win­ter ranges, to main­tain the var­i­ous habi­tats of O. hemionus. But, due to po­lit­i­cal op­po­si­tion to gov­ern­ment ac­qui­si­tion of pri­vately owned lands, plus a scarcity of funds for this pur­pose, only a small frac­tion of O. hemionus ranges has been ac­quired by the gov­ern­ment. The ef­fects of re­duced O. hemionus ranges can be mit­i­gated by bet­ter man­age­ment of the re­main­ing lands to max­i­mize their pro­duc­tiviy for O. hemionus. Var­i­ous habi­tat man­age­ment pro­grams in­clude the ma­nip­u­la­tion of live­stock graz­ing, the ma­nip­u­la­tion of cul­ti­va­tive com­mu­ni­ties, and the ma­nip­u­la­tion of veg­e­ta­tive com­mu­ni­ties. For O. hemionus, the op­ti­mal suc­ces­sional stages are sub­cli­max plant com­mu­ni­ties that can be per­pet­u­ated only through the in­flu­ence of hu­mans. Since O. hemionus pro­duc­tion is not the pri­mary man­age­ment goal on most pri­vate or pub­lic lands in west­ern North Amer­ica, O. hemionus habi­tat im­prove­ment pro­grams typ­i­cally in­volve a com­plex process of co­or­di­na­tion among bu­reau­cra­cies with mis­sions that are usu­ally not com­pat­i­ble (Wallmo 1981).

• IUCN Red List

  Least Concern
  More information

Other Com­ments

The an­nual cycle of antler growth in O. hemionus is ini­ti­ated and con­trolled by changes in day length act­ing on sev­eral cell types of the an­te­rior pi­tu­itary. These cell types se­crete growth-stim­u­lat­ing hor­mones that act mainly on the antlers and in­ci­den­tally on the testes. Antler hard­en­ing, shed­ding, and the breed­ing pe­riod are me­di­ated by de­creas­ing day length through the ac­tion of go­nadotropins on Ley­dig cells, thus pro­duc­ing an­dro­gens. An­dro­gens in­duce sec­ondary os­si­fi­ca­tion, ac­cel­er­ate mat­u­ra­tion, in­duce be­hav­ioral changes that re­sult in shed­ding antler vel­vet, and aid in the main­te­nance of os­teoblasts and os­teo­cytes to main­tain antlers in hard bone con­di­tion. With­drawal of an­dro­gens at the end of the breed­ing sea­son per­mits re­sorp­tion of bone at the pedi­cel-antler junc­tion and antler shed­ding. O. hemionus has ex­cel­lent binoc­u­lar vi­sion. While un­able to de­tect mo­tion­less ob­jects, O. hemionus is ex­tra­or­di­nar­ily sen­si­tive to mov­ing ob­jects. The sense of hear­ing is also ex­tremely acute. O. hemionus is a tar­get for var­i­ous viral, bac­te­r­ial, and par­a­sitic dis­eases. For ex­am­ple, heavy amounts of gas­troin­testi­nal ne­ma­todes may cause death in O. hemionus. This par­a­sitic dis­ease is usu­ally in­dica­tive of such pre­dis­pos­ing fac­tors as high mule deer den­sity and mal­nu­tri­tion. In­fec­tion by the par­a­sitic meningeal worm can cause fatal neu­ro­logic dis­ease in O. hemionus. Live­stock may trans­mit viral dis­eases to O. hemionus as seen in foot-and-mouth dis­ease. This in­fec­tion is char­ac­ter­ized by blis­ters in the mouth, above the hooves, and be­tween the dig­its (An­der­son 1984).

Con­trib­u­tors

Michael Mis­uraca (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

Geist, V. 1981. Be­hav­ior: adap­tive strate­gies in mule deer. Pp. 157-224, in Mule and Black-tailed deer of North Amer­ica (O. C. Wallmo, ed.). Univ. Ne­braska Press, Lin­coln, xvii + 605 pp.

Kucera, T. E. 1978. So­cial be­hav­ior and breed­ing sys­tem of the Desert mule deer. J. Mamm., 59:463-476.

Short, H.L. 1981. Nu­tri­tion and me­tab­o­lism. Pp. 99-127, in Mule and Black-tailed deer of North Amer­ica (O. C. Wallmo, ed.). Univ. Ne­braska Press, Lin­coln, xvii + 605 pp.

Wallmo, O. C. 1981. Mule and Black-tailed deer dis­tri­b­u­tion and habi­tats. Pp. 1-25, in Mule and Black-tailed deer of North Amer­ica (O. C. Wallmo, ed.). Univ. Ne­braska Press, Lin­coln, xvii + 605 pp.

An­der­son, A., O. Wallmo. 1984. Odocoileus hemionus. Mam­malian Species, 219: 1-9. Ac­cessed Oc­to­ber 30, 2006 at http://​www.​science.​smith.​edu/​departments/​Biology/​VHAYSSEN/​msi/​default.​html.