Scientists analyzed more than 20,000 hospital records of koala disease and death from 1997 to 2013.
Car accidents seem to be the major cause of koala death.
Chlamydia, a sexually transmitted disease that also affects humans, is the second most frequent cause of koala death in southeast Queensland.
Koalas in the state are also frequently killed by domestic dogs.
Koalas, the eucalyptus-loving cuddly marsupials found only in Australia, are declining rapidly.
In some areas, their numbers have plummeted by more than 80 percent, with koala populations in the state of Queensland being some of the worst hit.
Now, a new study suggests that cars and a sexually transmitted disease, Chlamydia, are to blame for their decline in south-east Queensland.
By analyzing more than 20,000 hospital records of koala disease and death from 1997 to 2013, researchers found that trauma due to collisions with cars was the most frequent cause of death in these animals.
Nearly a quarter of the koalas (Phascolarctos cinereus) hit by cars were otherwise in good health, the researchers report in the study published in Scientific Reports. This is worrying, they say, because it suggests that car accidents are removing healthy, breeding animals from the local populations.
The second most frequent cause of death among Queensland’s koalas appears to be Chlamydia, a sexually transmitted disease that also affects humans.
The strain of Chlamydia that infects koalas can have devastating effects. The disease affects both male and female koalas, and their babies can also get infected while suckling from their mothers in the pouch. Chlamydia can cause the animals to become blind, infertile, or develop urinary and respiratory infections, making it difficult for them to avoid predators or find food. The disease is believed to be prevalent across half the koala populations in Australia.
Koalas in Queensland are also frequently killed by domestic dogs, the study found. However, trauma by animal attacks has shown a slight but steady decrease over the past few years, the researchers write. This “may reflect the efforts from the QLD State sponsored Koala Plan to identify threats, incorporate careful planning of koala sensitive areas in development, and educate regarding responsible pet ownership,” they add.
“Based on this information and its own research with other koala care facilities, the research team has developed a database which, for the first time, provides accurate scientific information on the specific threats facing south-east Queensland koalas,” Queensland Environment Minister, Steven Miles said in a statement. “This is one of several projects funded by the State Government to boost our knowledge and understanding of the threats facing koalas, so we can ensure work to secure viable and healthy koala populations across the state is based on evidence and scientific research.”
Co-author of the study Rachel Allavena, an Associate Professor at the University of Queensland’s School of Veterinary Science, added: “It’s important data collected over the span of the koala population crash. Populations throughout ‘Koala Coast’ declined by about 80 per cent over this period, so this iconic and famous species is in real trouble in our area.”
The koala was previously listed as Least Concern on the IUCN Red List. But due to its dwindling numbers, the species was up-listed to Vulnerable in 2016. The Australian government also lists koala populations in Queensland and New South Wales as vulnerable to extinction.
The researchers hope that their findings will help government agencies, conservation groups, and hospitals better target resources to protect and treat these threatened animals.
- Viviana Gonzalez-Astudillo, Rachel Allavena, Allan McKinnon, Rebecca Larkin, Joerg Henning. Decline causes of Koalas in South East Queensland, Australia: a 17-year retrospective study of mortality and morbidity. Scientific Reports, 2017; 7: 42587 DOI: 10.1038/srep42587
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