The koala is not classified as an endangered species under Australia's Endangered Species Protection Act. In fact, the number of koalas in Australia is a matter of hot debate among scientists and conservationists.
Many individual populations, including Phillip Island's, are are under threat from habitat loss, dog attacks, and cars. The lack of genetic variation between and within koala populations is also a matter of concern. The declines have led authorities in New South Wales to classify the koala as vulnerable.
As many populations decline, others, such as those on nearby French Island and Kangaroo Island in South Australia, are at risk through overpopulation of their limited habitat. This leads to over-browsing and destruction of the trees (pictured) that sustain the koalas and other native species, threatening them with starvation.
In the past, koalas have been regularly removed from French Island and other high density Victorian populations to prevent habitat destruction and starvation. These animals have been translocated to other parts of Victoria. For this reason, the koala is now considered to be widespread throughout most suitable habitat in Victoria, and the species is not classified as threatened. Over-browsing has become a serious environmental and animal welfare problem in six isolated habitat patches across coastal Victoria. However, unoccupied habitat is rapidly running out, and alternatives to translocation are urgently required. Methods of koala birth control are now being trialed in Victoria, and preliminary results indicate that this may be a feasible means of reducing population growth rates in isolated populations (Menkhorst, Middleton & Walters 1998).
However, koala contraception is an extremely expensive solution, and one which diverts scarce funds away from other species. For this reason, there is an urgent need for habitat conservation and restoration, including wildlife corridors, to link isolated patches of habitat.
Habitat loss due to land clearance is the greatest threat to koalas. Other major threats are dog attacks, road trauma, and disease (Phillip Island Nature Park 1998).
Chlamydia is a bacterium that infects a wide range of animals, including birds, sheep, cattle, horses, pigs, cats, mice and humans. It is considered to be the main pathogen of koalas. Our knowledge of it, while not great has rapidly increased over the last decade or two (Reed 2002).
It is not certain how koalas have come to be infected with Chlamydia. Some of the possible explanations are via introduction of infected mammals to Australia on one or more occasions over the last 40,000 years, exposure to it during the koala's evolution, or or a combination of these factors. Whatever the case, most populations of koalas carry antibodies for the disease, indicating some level of exposure (Reed 2002).
Chlamydia causes chronic infections in koalas. The infections occur in the urogenital tract (C. pecorum) and the respiratory tract (C. pecorum and C. pneumoniae) and can cause infertility, blindness and ultimately death. The visible symptoms are conjunctivitis ('pink eye') and urinary tract infections causing incontinence, leading to a condition known as 'dirty tail' or 'wet bottom' (Reed 2002).
Chlamydia can be treated with antibiotics. This usually requires a daily dosage over a long term, so is only practical with a captive animal (Reed 2002).
Chlamydia is readily transmitted to young in the birth canal and via pap. Mating, and possible fighting and other incidental contact are also likely sources of infection (Reed 2002).
During the 1980s, the fertility rate of koalas on Phillip Island dropped to about 15 percent. This was attributed to chlamydial infection. At the same time, the rate on French Island, where the urogenital strain of Chlamydia is absent, was almost 100 percent. Given normal levels of mortality, koalas need a fertility rate of about 35 percent to maintain their numbers. There is no research into infection rates on Phillip Island at present. However, symptoms are not often observed. But then again, neither are mothers with young (Reed 2002).
It is thought that stress due to habitat loss and other threats, such as dogs and cars, increases the incidence of symptoms (Phillip Island Nature Park 1998).
During the last major survey of Koala Conservation Centre koalas in 2001, more than a third of the sample tested positive to Chlamydia. Despite this, we do not often see physical signs of the disease in the park, indicating that the level of infection is low (Reed 2002).
At the Koala Conservation Centre, we test the koalas for Chlamydia every few years. Generally, koalas would not be treated unless they were obviously unwell. In order to maintain numbers, we maintain a Chlamydia-free population of koalas in the close viewing area (Reed 2002).
Menkhorst, P., Middleton, D. and Walters B. (1998). Managing over-abundant koalas (Phascolarctos cinereus) in Victoria: A brief history and some potential new directions. In Managing marsupial abundance for conservation benefits. Society for Conservation Biology: Sydney.
Phillip Island Nature Park. (1998). Nature Notes: Everything you ever wanted to know about koalas. Phillip Island Nature Park: Cowes, Vic.
Reed, A. (2002). Koalas and Chlamydia. Friends of the Koala Inc. Newsletter, 48, pp. 3-4.
Site last updated Spring 2011. © Friends of the Koalas