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Phascolarctos cinereuskoala

By Jennifer Dubuc and Dana Eckroad

Geographic Range

The koalas live in eastern Australia and range from northern Queensland to southwestern Victoria. They have been introduced to western Australia and nearby islands (LPZ, 1997).

Habitat

Koalas are arboreal, remaining mostly in the branches of the eucalyptus trees, where they are able to feed and stay out of reach of their predators. The koala is confined to eucalyptus forests below 600 m.

Physical Description

Koalas from the southern end of the range are generally larger in size than their northern counterparts. In both areas they exhibit sexual dimorphism with the males being larger. In the south, males have an average head-body length of 78 cm and females 72 cm (MacDonald, 1984). The koala's have a vestigial tail. Average weights are: in the south, males--11.8 kg, females--7.9 kg; in the north, males--6.5 kg, females 5.1 kg (MacDonald, 1984) "Males are up to 50% heavier than females, have a broader face, somewhat smaller ears, and a large chest gland (MacDonald, 1984)." Females have two mammae; and rather than a chest gland, have a pouch that opens to the rear and extends upward and forward (Nowak, 1997). Koalas have dense, wooly fur that is gray to brown on top and varies with geographic location. There is white on the chin, chest and inner side of the forelimbs(MacDonald, 1984). The rump is often dappled with white patches and the ears are fringed with long white hairs (MacDonald, 1984). The coat is generally shorther and lighter in the north of range. The paws are large, and both fore and hind feet have five strongly clawed digits. On the forepaw the first and second digits oppose the other three which enables the koala to grip branches as it climbs. The first digit of the hind foot is short and greatly broadened while the second and third digits are relatively small and partly syndactylous but have separate claws (Nowak, 1997).

  • Range mass
    5.1 to 11.8 kg
    11.23 to 25.99 lb
  • Average basal metabolic rate
    5.744 W
    AnAge

Reproduction

Females are sexually mature at two years of age. Males are fertile at two years but usually don't mate until they reach four simply because competition for females requires larger size. Females are seasonally polyestrous, with an estrous cycle of about 27-30 days, and usually breed once every year (Nowak, 1997). The gestation period is 25-35 days with births occurring in mid-summer (December-January). Litters generally consist of only one young but twins have been reported (Nowak, 1997). The young weigh less than 0.5 grams when born, and attach to one of the nipples in the pouch. Young have a pouch life of 5-7 months, feeding on milk or predigested leaves that are nontoxic, and are weaned at 6-12 months (Nowak, 1997). Toward the end of their pouch life the young feed regularly on material passed through the mother's digestive tract (Nowak, 1997). Once the young begins to feed on leaves growth is rapid. The young leaves the pouch after seven months and is carried about on the mother's back. By eleven month's of age the young is independent, but may continue to live close to the mother for a few months. Koalas may live past 10 years in the wild, and there have been reports of life spans over 20 years in captivity.

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • sexual
  • Average number of offspring
    1
    AnAge
  • Average gestation period
    31 days
    AnAge
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    646 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    1095 days
    AnAge

Lifespan/Longevity

Behavior

Koalas are polygynous and relatively sedentary (MacDonald, 1984). Because of their low quality diet, koalas conserve energy by their behavior. They are slow-moving and sleep up to 18 hours a day (MacDonald, 1984). " Adults occupy fixed home ranges, the males usually 1.5-3ha, females 0.5-1ha (MacDonald, 1984)." For breeding males the home range will overlap those of females as well as subadult and non-breeding males. During the breeding season (October-February), adult males are very active at night and move constantly through their range, both ejecting male rivals and mating with any receptive females (MacDonald, 1984). During the breeding season males use loud bellowing calls, that consist of a series of harsh inhalations each followed by a resonant, growling expiration (MacDonald, 1984). These calls advertise an individual's presence and warn off other males. The only vocalization generally heard from females and subadult males is a harsh wailing distress call given when harrassed by adult males. Copulation is brief genrally lasting less than two minutes, and occurs in a tree (MacDonald, 1984). During mating the male will grasp the back of the female's neck with his teeth. Koalas are mainly nocturnal and completely arboreal. They come to the ground occasionally to move to another food tree or to lick up soil or gravel which aids in digestion (Nowak, 1997). Outside of the breeding season there is little obvious social behavior (MacDonald, 1984). Koalas live in loose-knit groups if enough suitable trees are present, but only one animal per tree (LPZ, 1997). The koala is primarily a solitary animal, although sometimes it lives in small harems led by a single male. Koalas are extremely slow-moving animals and are relatively defenseless.

Communication and Perception

Food Habits

Koalas are herbivorous feeding on both eucalypt and non-eucalypt species. However the bulk of their diet comes from only a few eucalypt species. Eucalyptus viminalis and E. ovata are preferred in the south, while E. punctata, E. camaldulensis and E. tereticornis are the taste of the north (MacDonald, 1984). The leaves are highly toxic; the animals get around this by having a flora of bacteria in their stomachs that metabolize the toxins of the leaves. Koalas have a highly specialized diet in which they eat only 20 of the 350 species of eucalyptus and prefer only 5 species. They feed at night. An adult koala can eat 500g daily. The koala has adapted to cope with its high fiber, low protein diet. "The cheek teeth are reduced to a single premolar and four broad, highly cusped molars on each jaw which finely grind the leaves for easier digestion (MacDonald, 1984)." In addition the koala's caecum is up to four times its body size.

Economic Importance for Humans: Positive

In the early 20th century the koala was hunted extensively for its warm, thick coat. However, they are now protected and can no longer be hunted.

Economic Importance for Humans: Negative

none noted

Conservation Status

The koala holds no special status although the Environment Australia Biodiversity Group calls the koala lower risk--near threatened (1996). Koalas were nearly exterminated at the turn of the century because they were hunted for their fur, and because their environments were destroyed by fires caused by humans. After1927 as a result of public outcry the koala became legally protected. Currently their main threat is habitat destruction. Management of the koala can be difficult. Populations that are protected can reach such high numbers in an area that they destroy the trees on which they feed. Often portions of populations have to be relocated in order to reduce the number of individuals in a given area. However, this is complicated by the shortage of suitable forest areas where surplus animals can be released (MacDonald, 1984).

They are also threatened by the microorganism Chlamydia psittaci, which can make them sterile.

Other Comments

Two interesting adaptations of the koala are: "Cheek pouches that allow the animal to store unchewed food while moving to a safer or more protected location.

The koala cools itself by licking its arms and stretching out as it rests in the trees (koalas have no sweat glands) (LPZ, 1997)."

Contributors

Jennifer Dubuc (author), University of Michigan-Ann Arbor, Dana Eckroad (author), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

References

Lincoln Park Zoo. 1997. Species Data Sheet: Phascolarctos cinereus. http://www.lpzoo.com/animals/mammals/facts/koala.html

Environment Australia Biodiversity Group. 1996. Action Plan for Australia's Marsupials and Monotremes. http://www.anca.gov.au/plants/threaten/marsup7.htm#phaciner

MacDonald, D. 1984. Encyclopedia of Mammals. Facts on File Publications, NY.

Nowak, R.M. 1997. Walker's Mammals of the World. Fifth Edition. Johns Hopkins University Press, Baltimore. Online Version: http://www.press.jhu.edu/books/walker

The New Grolier Multimedia Encyclopedia, "Koala", 1993, Grolier Inc.

Encyclopedia Americana, vol.16, "Koala", pg. 562, 1986, Grolier Inc.

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