How do human activities impact koalas?

The koala (Phascolarctos cinereus) is an iconic Australian species primarily found in eucalypt forests along the eastern and southeastern coasts of Australia. Despite their uniqueness and popularity, koalas face numerous threats to their survival, primarily due to human activities. Ongoing habitat destruction, fragmentation, and alteration has severely impacted population numbers exposing them to many significant threats including starvation and exposure due to lack of shelter, predation by dogs, collisions with vehicles, and disease. Additionally, recent bushfires and drought events have further exacerbated their vulnerability.

Habitat loss

Koalas are listed as vulnerable under the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, with Queensland, New South Wales, and the Australian Capital Territory declaring koalas as endangered in February 2022 [1]. One of the most significant threats to koalas is habitat loss, driven primarily by urbanisation, deforestation, and land clearing for agriculture (including timber harvesting). As human populations expand, natural habitats are increasingly being converted into urban and agricultural landscapes, depriving koalas of their food sources and shelter and exposing them to hazards. Data collected by the Port Macquarie Koala Hospital over a nine-year period found that nearly half of the admissions were associated with human activities. For example, 24.9% of koalas admitted were found in a dangerous area (e.g. motorways, telegraph poles or in urbanized areas), followed by vehicle collisions (17.4%) and dog attacks (7.4%) [2].

Koalas are renowned as specialist folivores, meaning they have a highly specialised diet primarily comprising eucalyptus leaves of two to seven particular tree species present in their home range. This dietary specialisation has evolved over millions of years, allowing koalas to efficiently extract nutrients from the tough, fibrous leaves of eucalyptus trees, giving them a competitive edge with other folivores. However, this specialisation also makes koalas highly dependent on specific plant species, and as a result, habitat loss and land clearing, be it for urban development, road infrastructures, agriculture or coal mining, have devastating and multifactorial impacts on koala populations [3].

Energy expenditure and competition

The loss of native forest cover reduces the availability of trees koalas can use as shelter from predators, shelter from extreme climatic events like heatwaves, and as a food source. As a result, increased competition for vital resources leads to aggression resulting in some individual koalas travelling more frequently, for longer distances and using more energy to forage and survive.

Predation

To meet their nutritional requirements in a fragmented habitat, koalas are forced to move in barren or nutritionally poor landscapes, meaning not only are they unable to feed for extended periods but they are also more exposed to predation, particularly by dogs. Predation results in fear, stress, anxiety, pain and death.

Vehicle collisions

When their habitat is cleared for new road infrastructures, koalas must cross roads to move between viable patches of vegetation within their home range. This leads to increased collisions with vehicles, especially when the roads being crossed have high speed limits. The impact of vehicle collisions on koala populations is concerning with statistics suggesting an average of 400 koalas dying each year in South-East Queensland [4].

Physical injury

In addition to predation and vehicle collisions, koalas are injured due to land clearing and tree harvesting (including plantation timber). Despite the use of different detection methods, it is still extremely difficult to spot individuals due to koalas being well camouflaged between the leaves of top branches of eucalyptus trees and usually being present at low densities. Even with the use of spotlighting, scat surveys or the deployment of acoustic sensors and heat-detecting drones, it is very difficult to confidently determine if any individuals inhabit a specific area. Therefore, tree-harvesting activities often result in serious injuries and/or death of koalas nestled up in the trees that are cut down [5,6].

Stress and disease

Koalas living in trees adjacent to land clearing are also impacted. Increased levels of stress hormones have been found in wild koala populations exposed to habitat clearance, bushfires, droughts and other environmental stressors, which can increase susceptibility to disease. For example, Chlamydia, a sexually transmitted disease, has become increasingly prevalent in koala populations in recent decades. Some koala populations in NSW had been able to cope with the disease for years until the significant environmental stressors due to nine heatwaves in 2008 caused a decrease of their immune defenses and rendered them susceptible to chlamydiosis [7,8].

What needs to be done?

Human activities pose significant threats to koalas, ranging from habitat loss and fragmentation to distress and disease spread resulting in injury, suffering and death. There is an urgent need to fully understand the impact of land clearing to enable the development of effective conservation strategies to help safeguard koala populations into the future.