The smaller a Koala is the more vulnerable they are to the different predators out there. Due to the fact that humans live in close proximity to the Koalas, there are thousand deaths annually that are the result of dog attacks. These dogs view the Koala as some type of enemy. read more
Aside from humans and some of the animals they have introduced to Australia (dogs, foxes) predators of the koala apparently include dingoes, large owls and eagles, large goannas (predatory lizards) and pythons. A couple of thousand years ago they also would presumably have been vulnerable to thylacines. read more