Koalas are essentially solitary animals, with very little social interaction other than during the breeding season. Adults occupy fixed home ranges. Range size depends on the pro-
A Queensland koala (Phascolarctos cinereus adustus) showing its chest gland and secretion. (Photo by Kenneth W. Fink/Photo Researchers, Inc. Reproduced by permission.)
Koalas are largely nocturnal, feeding and moving after dusk. They rarely leave the security of the trees, descending to the ground only to move to another food tree, or to consume soil, which aids digestion. Koalas walk on four legs, run with a bounding gait, and can swim if necessary.
As one adaptation to their low-energy eucalyptus leaf diet, koalas sleep up to 20 hours a day, usually wedged comfortably into the fork of a tree. Even when awake, koalas spend much time resting, and feeding occupies only 10% of their day.
Activity livens up in the summer breeding season, when dominant males will attempt to defend their territory for breeding rights with resident females. At this time of year males use their chest gland to scentmark tree trunks and can often be heard bellowing, apparently to warn off rival males and attract females. This deep, grunting bellow often provokes responses from other males in the area. At night males move around more, fighting with any competing adult males that they encounter, or mating with estrous females.
Koalas have a range of other sounds for communication. Mothers and babies make soft clicking, squeaking sounds, and
gentle murmuring, or will grunt if annoyed. All koalas are capable of a distressing, high-pitched cry like a screaming baby when afraid.
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