Musk Ox

Musk Ox

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Description

Musk oxen have barrel-shaped bodies with short legs.  They are covered with fur except for the small area between the nostrils and lips.  Both sexes have cream-colored horns with black tips that grow together at the center of the head, drop down along side of head, then curve up to form sharp hooks.  These horns grow with age.  The tail is short (two to four inches) and is entirely covered and hidden under the fur.  Fur can be divided into two types: Guard hair and qiviut (pronouced kiv-ee-ute). Guard hairs are the continuously growing dark hairs that create the long, shaggy coat.  They can grow long enough to brush the ground on older musk oxen.  This long hair is sometimes referred to as a skirt.  The back is marked by a lighter patch of brown or cream where the guard hairs are shorter.  This is referred to as the saddle.  Older adults sometimes develop a large mane of fur that sits on the shoulders.  The guard hairs act as protection against wind and precipitation, as well as insects.  Qiviut is the insulating winter coat. It begins growing in fall and is shed through the guard hair in the spring.

Lifestyle

Musk oxen are a social species and much of their behavior is based on the harem breeding system.  They live in herds as small as five during the summer, and may join with other small groups to form herds as large as 60 individuals in the winter. These larger groups provide protection from both the elements and predators. Other advantages include being easier to spot in a large group if one member becomes lost.  Most herds average between 10 and 20 animals.  Musk oxen have many adaptations to the cold (such as short legs, thick fur, and high body fat), that limit their mobility.  Though muskoxen can run as fast as 25 miles per hour, they can easily overheat.  For this reason, the musk ox is generally slow moving and has very short migrations within the home range.  However, under certain conditions (weather permitting), calves as well as adults will play by head butting and chasing, as well as grunting and bellows.  Sometimes males are forced out of the herds during breeding season.  Among females, dominance is determined by age and size.  The larger, older females are dominant over the younger, smaller females through pushing, shoving, and chasing.  Calves are generally lowest in the hierarchy, although they determine dominance amongst themselves through chasing, mounting, and play. Generally, the higher the dominance status of the musk ox, the better its food supply and breeding rights.  Home ranges in Alaska are reported to be very large in the summer, 86 square miles, and much smaller in the winter and calving seasons, ranging from 10 to 27 square miles.  Musk oxen will typically stay in areas near water during summer months and then move to higher ground where wind will blow off much of the snow covering food during the winter.

Food Habits

Muskoxen are generalized grazers.  As calves, they are dependent upon the milk of their mothers for up to 1 year.  Within weeks of birth, they begin incorporating the adult foods into their diet.  In the summer months, the diet includes grasses, leafy plants, sedges, mosses, shrubs, herbs, and generally any vegetation available.  The fecal matter of the animals at this time is very moist and still has high levels of nutrients available.  In the winter months, the diet changes to willow, dwarf birch stems, roots, mosses, lichen, and any vegetation they can locate under or above the snow.  The fecal matter during these months is very dry and has very few nutrients left after the animals have digested the food.

Lifecycle

Musk oxen are considered a harem breeder in which one dominant male attempts to mate with all of the estrus females of the herd.  Beginning in late summer and into fall, males compete for dominance using very ritualized behaviors.  Males attempt to intimidate each other through posturing, roaring, head swinging, urinating on forefeet with strong scent markers, displaying sides to show size, and head butting.  During head butting, males face each other up to 45 meters apart, then charge up to 20 or 25 miles per hour and crash together on the horn bosses (areas of thick horn and bone on the forehead of males). They can repeat this procedure up to 10 or 12 times or until one of the males cannot continue or runs away.  This behavior is rarely fatal.  Males that compete for dominance are typically between the ages of 6 and 8 years old.  Older bulls are usually not strong enough, and younger males are typically not large enough, to compete.  Competition between bulls sometimes results in solitary males.  Once dominance is determined, a bull attempts to keep the females close together to defend them from other males.  Dominant males may breed multiple times with each female during one season.  Young musk oxen and non-dominant bulls typically keep their distance from the breeding harem.  Breeding occurs from late August into September and birth between mid-April and mid-May.  Muskoxen usually have single offspring after a gestation of about 8 months.  Twins are very rare and do not usually survive.  Generally, within 45 minutes of birth, calves are standing and nursing.  Calves typically weigh 20 to 22 pounds at birth and can gain up to 1 pound a day.  Though calves are born with a layer of baby qiviut and brown fat, they are dependent upon their mothers for warmth and food for their first winter, sometimes longer.  Calves start eating adult food within weeks of birth, although they continue to nurse for ten months to one year.  They may nurse longer depending on food availability, birth of a new calf, or temperament of the cow.  Musk ox calves follow their mothers and hide underneath the her skirt of guard hair.  Females reach sexual maturity between 1 and 4 years of age, depending on body condition, and will calve alternate years.  Calving every year is possible if food is available.  Males reach sexual maturity between 3 and 4 years.  During attack from predators, calves are often pushed behind the rumps of the adults, or into the middle of a circle formation.  Mothers also teach calves the social hierarchy behaviors by playing "games" such as king of the mountain, and mock head butting.  Males are not reported to directly care for the young.  However, since these animals are social, it is likely that the adult male in a herd helps to protect the young in the herd.

Population Status, Threats & Conservation

Though herds of musk ox native to Alaska and parts of Europe were driven to extinction through hunting pressures and climate fluctuations in the late 1800's, the species has been successfully reintroduced from surviving populations in Canada and Greenland and is doing well.  A small number of musk oxen originally from Greenland were reintroduced on Alaska's Nunivak Island in 1935-1936.  The population grew over the years and supplied animals for other reintroduction efforts in northern Alaska from 1968 to 1981.  Today, a population of about 2,300 muskoxen resides in Alaska.  Musk ox hunting is permitted in Alaska, but strictly controlled to keep population numbers stable or increasing.

Sources:
Musk Ox species profile, Alaska Department of Fish and Game
U.S. Fish and Wildlife Service, Musk Ox species profile
National Geographic, Musk Ox page
Elder, S., Mammology and L. Olson. 2005. "Ovibos moschatus" (On-line), Animal Diversity Web