Koalas are one of Australia’s most iconic marsupials, but they face a complex array of threats challenging their long-term survival in the wild. Due to significant population declines, the koala population across Queensland, New South Wales, and the Australian Capital Territory was officially uplisted to endangered status in February 2022. The dangers facing these animals extend beyond traditional predation, encompassing factors related to human expansion, widespread disease, and large-scale environmental shifts. Understanding these multifaceted threats is necessary for effective conservation efforts.
Natural Predators
Koalas generally have few natural predators because they spend most of their time high in the canopy of eucalypt trees, often sleeping for up to 20 hours a day. They become vulnerable when they descend to the ground to move between trees or find water. Australia’s native wild dogs, the dingoes, are considered primary natural predators, accounting for a large percentage of predation deaths in some areas.
Young koalas (joeys) are particularly susceptible to predation, even while still in the safety of a tree. Large birds of prey, such as the powerful owl and the wedge-tailed eagle, hunt joeys from the branches. Occasional threats also come from large reptiles like goannas and carpet pythons, which prey on smaller or injured koalas.
Human-Caused Dangers
The most pervasive threats result directly from human development and activity, making them the leading cause of mortality in many populations. Habitat destruction and fragmentation remain the biggest threat, driven by urban expansion, agriculture, and land clearing. Clearing eucalypt forests deprives koalas of their specialized food source and shelter, forcing them onto the ground more frequently.
When koalas move across fragmented landscapes, they face dramatically increased risks from motor vehicles. Collisions with cars are a major cause of death, especially where roads cut through former koala habitat. Studies show that nearly half of koalas admitted to wildlife hospitals suffer trauma linked to human activities, primarily vehicle strikes and dog attacks.
Domestic dog attacks are another significant danger, separate from wild dingo predation, and are concentrated in peri-urban areas. Koalas are highly vulnerable when they are on the ground, which is where over 66% of koala deaths occur. Fencing and poorly planned residential areas also restrict koala movement, preventing access to necessary food trees and mates.
Disease and Health Crises
Infectious diseases significantly impact koala survival and reproductive success. The most well-known biological threat is Chlamydia, a bacterial infection caused primarily by Chlamydia pecorum. This disease causes severe health problems, including painful conjunctivitis that can lead to blindness, urinary tract infections, and reproductive tract infections resulting in female infertility.
The impact of Chlamydia is often worsened by the presence of Koala Retrovirus (KoRV), which is similar to HIV. KoRV is found throughout many koala populations and is linked to immune suppression, making the marsupials more susceptible to secondary infections like Chlamydia. High levels of the retrovirus increase the risk of developing chlamydial disease symptoms by over 200%.
KoRV is also directly implicated in the development of cancers, particularly lymphosarcoma and leukemia. The combination of widespread immune suppression from KoRV and the debilitating effects of Chlamydia creates a double burden that severely limits the ability of populations to recover.
Environmental Catastrophes
Large-scale environmental events alter koala habitat and push them past their physiological limits. Catastrophic bushfires, such as the 2019–2020 “Black Summer” fires, have devastated millions of hectares of eucalypt forest, killing thousands of koalas and destroying their long-term food supply. Fires also increase stress, making surviving koalas more susceptible to diseases like Chlamydia.
Increased frequency and intensity of drought and heat stress pose a challenge to the species. Koalas typically obtain most moisture from eucalypt leaves, but prolonged drought makes the leaves less nutritious and hydrating. High temperatures, often exceeding 37.7 degrees Celsius, lead to severe dehydration and heat exhaustion, forcing koalas to descend to the ground in search of water where they face other dangers.