The koala Phascolarctos cinereus
The koala (Phascolarctos cinereus)
The koala is the only member of the family Phascolarctidae. This lovely little animal has a large head with big round ears covered with thick fur, small eyes set far apart, spoon-shaped nose, and dense, wooly fur. It also has large claws, except for on the first digit of the hind paw. The first and second digits of the paws are opposed like thumbs to help grip branches. Koalas occur in eucalypt forests of eastern Australia, from the north of Queensland to the south of Victoria.
The koala was first encountered in 1798 by the leader of an expedition to the Blue Mountains. In 1802, French-born explorer Francis Barrallier bought parts of killed koalas from his two Aboriginal guides. The first living koala in Europe arrived in 1881, purchased by the Zoological Society of London. Sadly, beautiful fur of koalas attracted many hunters. The koala was heavily hunted by European settlers in the early 20th century; e.g., 57,933 koala pelts were sold in Sydney in 1908 and more than two million pelts were exported from Australia by 1924. Dramatic decline of the wild populations of koala and the threat of species extinction triggered conservation actions; a number of nature reserves were established to save this species.
The koala spends most of its time in the branches of eucalypt trees where it can feed, coming down to the ground just to climb another tree, located too far to jump over onto its branches. These slow animals are able to skilfully jump and when escaping from their enemies, they run at a fast gallop, and then quickly climb up the nearest tree. During daytime, the koalas are sleeping on the branches or forks of the tree trunks. Even when awake, koalas may sit still for hours, clasping a branch or trunk of the tree with their forearms. Slow lifestyle of the koala is associated with its diet. The bulk of koalas’ diet comes from shoots and leaves of eucalypt trees. Eucalyptus leaves are very fibrous, low in protein content, and highly toxic for most animals (they even contain cyanide compounds). To avoid intoxication koalas select eucalypt species that contain lower levels of phenolic compounds, preferring trees growing on rich soils (especially along rivers), which have less toxins in their leaves than the trees growing on poor soils. A very slow metabolic rate (almost two times slower than metabolic rate in most mammals) allows koalas to cope with low nutritional value of their diet. Each koala eats approximately 0.5 to 1.1 kg of leaves per day. The animals use their specialized cheek teeth to grind the leaves into a fine paste which is then digested by micro organisms in the caecum part of the intestine. The koala’s caecum is unusually long, reaching the length of around 2.4 meters. The caecum contains millions of bacteria breaking down the fibre into substances which are easier to absorb. Since eucalypt leaves have a high water content, the koala does not need to drink often; it only drinks during long periods of drought. Sometimes koalas eat soil to compensate for mineral deficiency.
Koala females are solitary, and rarely leave their home territory. The males are not territorial but they demonstrate even more asocial behaviour; when two males encounter each other, they often attack the competitor, and may inflict an injury. Period from October through February is the only time when koalas may live in groups consisting of an adult male and several females. In this period, males often mark trees by rubbing the chest gland against the trunk or a branch, and produce loud bellows that can be heard from a distance of over one kilometre. Gestation in females lasts 30-35 days and results in the birth of a single young which has the body length of 15 to 18 cm, and weighs about 5.5 grams. The joey remains in the safety of the pouch until it is weaned at about 6 months of age, then clings onto the mother's back where it stays for another few months. At the age of 30 weeks, the joey starts eating semifluid excrements of its mother, which consist of partly digested eucalypt leaves; in this way the joeys obtain micro organisms required for the digestion process. Young koalas become independent at the age of one year; young females disperse when they are 12 to 18 months old, while the males often remain with their mothers until they are two to three years old.