The Koala is well suited to life in the trees. The koala has an excellent sense of balance and its body is lean and muscular and its quite long, strong limbs support its weight when climbing. The arms and legs are nearly equal in length and the koala's climbing strength comes from the thigh muscle joining the shin much lower than in other animals. Its paws are especially adapted for gripping and climbing with rough pads on the palms and soles helping it to grip tree trunks and branches. Both front and hind paws have long sharp claws and each paw has five digits. On the front paw, two fingers are opposed to the other three, rather like a human's thumb, so they are able to be moved in opposition to the fingers. This allows the koala to grip more securely. On the hind paw, there is no claw on the big toe, and the second and third toes are fused together to form a 'grooming claw'. Koalas have a thick woolly fur which protects them from both high and low temperatures.It also acts like a 'raincoat' to repel moisture when it rains. The fur varies in colour from light grey to brown, with patches of white on the chest and neck, inside arms and legs and inside the ears. Mature males are recognisable by the brown 'scent gland' in the centre of their white chest. The fur on the koala's bottom is densely packed to provide a 'cushion' for the hard branches it sits on, and has a 'speckled' appearance which makes koalas hard to spot from the ground. An adult male koala can weigh between 8 and 14 kilograms and a female between 6 and 11 kilograms, with the heavier animals coming from the southern areas where they have adapted to the colder climate by an increase in body weight and thicker fur. If you see Koalas in Queensland, they look noticably smaller than Koalas from Victoria. Koalas are mostly nocturnal animals and they are most active during the night and at dawn and dusk. This is because in the cooler hours they are less likely to lose precious moisture and energy than they would during the hotter daylight hours. An average of eighteen to twenty hours each day are spent resting and sleeping, and the remainder for feeding, moving around, grooming and social interaction. The Koala's nose is one of its most important features, and it has a very highly developed sense of smell. This is necessary to differentiate between types of gum leaves and to detect whether the leaves are poisonous or not. The Koala's digestive system is especially adapted to detoxify the poisonous chemicals in the leaves. The toxins are thought to be produced by the gum trees as a protection against leaf-eating animals like insects. Trees which grow on less fertile soils seem to have more toxins than those growing on good soils. This could be one reason why koalas will eat only certain types of eucalypts, and why they will sometimes even avoid them when they are growing on certain soils.

• published: 15 Sep 2013
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