Rescue teams go into the field to pick up sick or injured animals. They are treated and then returned to the wild. According to Dr Ken Phillips, who runs the NY office of the Koala Preservation Society of New South Wales, the hospital's governing body, Koalas exhibit remarkable intelligence. They tend to sense when humans are trying to help them, and can often be treated without tranquilizers even when in pain or frightened. This is a complicated question.
Koalas fall prey to many of the same side effects of civilization which affect many wild animals.
They are often hit by cars or poisoned by toxic waste. But they also have a unique problem. Koalas do not drink water, but hydrate themselves entirely from Eucalyptus. The Eucalyptus also serves another purpose. If the corridors they know are removed by developers, they will not mate.