Animal Diversity Web

Ge­o­graphic Range

While their do­mes­ti­cated coun­ter­parts can be found in a much more var­ied area in the ori­en­tal re­gion, the main ge­o­graphic range of wild B. grun­niens is lim­ited to the Ti­betan Plateau, which in­cludes "...​the west­ern edge of Gansu Province, Qing­hai Province, the south­ern rim of the Xin­jiang Au­tonomous Re­gion, and the Tibet Au­tonomous Re­gion." (Schaller & Wulin, 1995).

• Biogeographic Regions
• palearctic
  • native
• oriental
  • native

Habi­tat

The habi­tat of B. grun­niens can vary, but mainly con­sists of three areas with dif­fer­ent veg­e­ta­tion: Alpine meadow, alpine steppe, and desert steppe (Schaller & Wulin, 1996). Each habi­tat fea­tures large areas of grass­land, but dif­fer in the type of grasses/small shrubs, amount of veg­e­ta­tion, av­er­age tem­per­a­ture, and pre­cip­i­ta­tion.

The habi­tat for B. grun­niens can also be de­pen­dent on the sea­son. Some herds will mi­grate large dis­tances sea­son­ally to feed on grass, moss, and lichens. How­ever, B. grun­niens by most ac­counts does not care for warm weather and, pre­fer­ring the colder tem­per­a­tures of the plateaus, will re­turn when sea­sonal tem­per­a­tures start to warm (Buch­holtz, 1990).

In more re­cent years, B. grun­niens has been in­creas­ingly con­fined to the desert steppe. This is in part due to the fact that farm­ers mov­ing into the re­gion don't find the land and min­i­mal pre­cip­i­ta­tion (50-100 mm/yr) de­sir­able. Yaks are thus not dis­turbed by human ac­tiv­i­ties in this re­gion (Schaller & Wulin, 1996).

• Habitat Regions
• temperate
• polar
• terrestrial

• Terrestrial Biomes
• tundra
• mountains

• Range elevation

  3200 to 5400 m

  10498.69 to 17716.54 ft

• Average elevation

  4500 m

  14763.78 ft

Phys­i­cal De­scrip­tion

Wild yak males can be up to 3,250 mm in length and more than 2,000 mm in height. Av­er­age weight for male B. grun­niens is 1,000 kg with the fe­male being around 300 kg (Nowak, 1999). Do­mes­tic yaks can be con­sid­er­ably smaller in weight, with males rang­ing from 350 to 580 kg and fe­males be­tween 225 to 255 kg (Buch­holtz, 1990).

Other phys­i­cal fea­tures of B. grun­niens in­clude: a black­ish brown pelage, large black up­ward curv­ing horns, and long hair cov­er­ing the body in­clud­ing the tail (Nowak, 1999). In con­trast, do­mes­ti­cated pop­u­la­tions have shorter legs, broader hooves, more var­ied pelage col­oration, and weaker horns which some­times can be ab­sent al­to­gether (Buch­holtz, 1990).

Both wild and do­mes­ti­cated yaks pos­sess large lungs, a high red blood cell count, and higher con­cen­tra­tion of he­mo­glo­bin than most other bovids. All of these fac­tors allow the yak to live and thrive in higher el­e­va­tions that would give other, non-ac­cli­mated an­i­mals el­e­va­tion sick­ness (Sum­mers, 1997).

• Other Physical Features
• endothermic
• bilateral symmetry

• Range mass

  300 to 1000 kg

  660.79 to 2202.64 lb

• Range length

  3250 (high) mm

  127.95 (high) in

Re­pro­duc­tion

For most of the year, male and fe­male wild yaks spend their time in sep­a­rate herds. While fe­males and young (oc­ca­sion­ally in­clud­ing some young males) usu­ally stay in large herds, males tend to ei­ther spend their time alone or in small groups. Dur­ing the mat­ing sea­son, males leave their groups and join with the fe­male herds. Males com­pete for ac­cess to re­cep­tive fe­males, often vi­o­lently. (Nowak, 1999; Buch­holtz, 1990)

• Mating System
• polygynous

The mat­ing sea­son for B. grun­niens starts in Sep­tem­ber, with births usu­ally oc­cur­ing in June (Buch­holtz, 1990).

In the wild, the fe­male B. grun­niens have one calf every other year. Ges­ta­tion is about 9 months, wean­ing oc­curs at one year, and full size is ob­tained in 6-8 years. At this age sex­ual ma­tu­rity is also at­tained. For the do­mes­ti­cated yak the re­pro­duc­tive cycle is more var­ied, with the cow some­times giv­ing birth to more than one calf per year (Nowak, 1999).

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
  • internal
• viviparous

• Breeding season

  In wild yak the mating season begins in September, with births occurring in June (Nowak, 1999).

• Range number of offspring

  1 (low)

• Average number of offspring

  1

• Average number of offspring

  1

  AnAge

• Average gestation period

  9.33 months

• Average gestation period

  274 days

  AnAge

• Range weaning age

  5 to 9 months

• Range age at sexual or reproductive maturity (female)

  6 to 8 years

• Range age at sexual or reproductive maturity (male)

  6 to 8 years

Most of the parental care of young is done by the fe­male due to the na­ture of wild fe­male and male B. grun­niens to spend the ma­jor­ity of the year in sep­a­rate groups (Buch­holtz, 1990). Young are born able to stand and walk within sev­eral hours after birth.

• Parental Investment
• altricial
• female parental care

Lifes­pan/Longevity

In the wild, the max­i­mum lifes­pan of B. grun­niens is lim­ited to about 25 years.

• Range lifespan
  Status: wild

  25 (high) years

• Average lifespan
  Sex: female
  Status: wild

  25.0 years

  Max Planck Institute for Demographic Research

Be­hav­ior

Wild yak spend most of their time graz­ing, some­times mov­ing to and from var­i­ous areas de­pend­ing on the sea­son. They are mainly ac­tive dur­ing the day. They live in herds which can vary in size from 20 to 200 in­di­vid­u­als (Buch­holtz, 1990). How­ever, a more re­cent sur­vey of the Chang Tang Re­serve by Schaller & Wulin (1995) found smaller herds; Usu­ally 2 to 5 in­di­vid­u­als for soli­tary male herds, and 6 to 20 in­di­vid­u­als in mainly fe­male herds. Fe­males and males live sep­a­rately for most of the year. Male bulls usu­ally band to­gether in groups of 10-12, while fe­males and young can com­prise a much larger group (from as lit­tle as 10-12 to per­haps 200 in­di­vid­u­als).

An­other in­ter­est­ing be­hav­ior of wild B. grun­niens is that, for un­known rea­sons, they will some­times at­tack an kill their do­mes­ti­cated coun­ter­parts (Buch­holtz, 1990).

• Key Behaviors
• motile
• nomadic
• social
• dominance hierarchies

Com­mu­ni­ca­tion and Per­cep­tion

• Perception Channels
• tactile
• chemical

Food Habits

Bos grun­niens is a grazer, with a diet com­posed mainly of var­i­ous low-ly­ing grasses and grass-like plants, in­clud­ing shrubs, forbs, cush­ion plants, etc., found on the Ti­betan plateau, though they will also con­sume lichen, mosses, and forbs (Schaller & Wulin, 1995).

• Primary Diet
• herbivore
  • folivore

• Plant Foods
• leaves
• bryophytes
• lichens

Pre­da­tion

At signs of dan­ger, wild herds of B. grun­niens will run from the threat. Other ac­tions that they will take in­clude loud snort­ing and charg­ing at the per­ceived threat (Buch­holtz, 1990).

• Known Predators

  • Tibetan wolves (Canis lupus)
  • humans (Homo sapiens)

Ecosys­tem Roles

Through their graz­ing ac­tiv­i­ties, yaks play an im­por­tant role in nu­tri­ent re­cy­cling and in gen­er­at­ing in­ter­me­di­ate lev­els of dis­tur­bance in their ecosys­tems. They are also an im­por­tant prey species for wolves.

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Do­mes­tic:

With wide hooves and the abil­ity to carry large weights at high el­e­va­tions, do­mes­ti­cated yak serve as beasts of bur­den for many in­hab­i­tants of the Ti­betan plateau. The finer fur of the young is used for cloth­ing, while the longer fur of the adult is used in mak­ing blan­kets, tents, etc. Also, in some areas where fire­wood is par­tic­u­larly sparse, the dung is used as fuel. In some areas, milk from the cow is used to pro­duce large amounts of but­ter and cheese for ex­port (Buch­holtz, 1990).

Wild:

The wild coun­ter­part of B. grun­niens serves many of the same eco­nomic func­tions, al­though to a lesser de­gree due to their rather sparse avail­abil­ity and ob­vi­ous non-do­mes­ti­ca­tion. While penal­ties have been set by China, hunt­ing of the wild yak still takes place, es­pe­cially in the win­ter where some local farm­ers find them the only source of meat dur­ing harsh win­ter months (Schaller & Wulin, 1996).

• Positive Impacts
• food
• body parts are source of valuable material
• produces fertilizer

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There are sev­eral neg­a­tive eco­nomic im­pacts on hu­mans. Where wild and do­mes­ti­cated B. grun­niens live in close prox­im­ity to one an­other, wild yak have been known to break down fences. In some ex­treme cir­cum­stances, wild yaks have been known to kill do­mes­ti­cated yak (Buch­holtz, 1990).

The pos­si­bil­ity of the trans­mis­sion of dis­ease be­tween do­mes­tic and wild B. grun­niens is also a con­cern in areas where the two live fairly close to one an­other, and per­haps have lim­ited con­tact (Schaller & Wulin, 1996).

• Negative Impacts
• causes or carries domestic animal disease

Con­ser­va­tion Sta­tus

There are many fac­tors that are cur­rently lead­ing to a de­cline in the num­ber of wild B. grun­niens, which is cur­rently es­ti­mated at around 15,000. Per­haps one of the largest has been hunt­ing by hu­mans. Ac­cord­ing to Schaller and Wulin (1995), while the Tibet For­est Bu­reau is mak­ing sub­stan­tial ef­forts to pro­tect yak (in­clud­ing fines of up to $600), "Hunt­ing is dif­fi­cult to sup­press with­out a mo­bile pa­trol force, as the re­cent dec­i­ma­tion of wildlife in the Arjin Shan Re­serve has shown."

Also, as pas­toral­ists are start­ing to change their habits from a no­madic to seden­tary lifestyle their habit is be­gin­ning to be­come fenced off. The in­tro­duc­tion of do­mes­ti­cated yaks (via the pas­toral­ists) also pre­sents prob­lems in re­gards to the trans­mis­sion of dis­ease (e.g. bru­cel­losis), and pos­si­ble in­creased com­pe­ti­tion for the same graz­ing land (Schaller & Wulin, 1995).

Do­mes­ti­cated yak are not listed as en­dan­gered due to their large num­bers.

• IUCN Red List

  Vulnerable

• US Federal List

  Endangered

• CITES

  Appendix I No special status

Con­trib­u­tors

Matthew Oliphant (au­thor), Uni­ver­sity of North­ern Iowa, Jim De­mastes (ed­i­tor), Uni­ver­sity of North­ern Iowa.

Ref­er­ences

Buch­holtz, C. 1990. True Cat­tle (Genus *Bos*). Pp. 386-397 in S Parker, ed. Grz­imek's En­cy­clo­pe­dia of Mam­mals, Vol­ume 5. New York: Mc­Graw-Hill Pub­lish­ing Com­pany.

Nowak, R. 1999. Walker's Mam­mals of the World, 6th Edi­tion, Vol­ume II. Bal­ti­more: Johns Hop­kins Uni­ver­sity Press.

Schaller, G., L. Wulin. 1995. Dis­tro­bu­tion, Sta­tus, and Con­ser­va­tion of Wild Yak (*Bos grun­niens*). Bi­o­log­i­cal Con­ser­va­tion, 76: 1-8.

Sum­mers, D. March-April 1997. Moun­tain Ma­chine. In­ter­na­tional Wildlife, 27 no. 2: 36-42.