Drop, bears: chronic stress and habitat loss are flooring koalas

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Koalas are stressed out by a range of pressures, from habitat loss to dog attacks.
Edward Narayan, Author provided

Edward Narayan, Western Sydney University

Koalas are under a lot of stress. Heatwaves, land clearing and even noise pollution are all taking a toll.

Each year, hundreds of koalas are taken to veterinary clinics after being rescued from roadsides or beneath trees, and the incidences increase during the summer months.

Chronic and ongoing pressures such as habitat destruction are overwhelming koalas’ ability to cope with stress. Koalas are nationally listed as vulnerable, so it’s important to understand how they are affected by threats that can reduce life expectancy and their ability to cope with problems.

What is stress?

The term “stress” was coined in 1936 by Hans Sayle after experiments on rats. Sayle demonstrated that the adrenal glands, which sit on top of the kidney and produce the stress hormones adrenaline and cortisol, can swell in response to any noxious stimulus or due to pathological state. In addition, there are changes in the tissues and glands involved in the basic functioning of the immune system, reproduction and growth.

Read more: What happens to your body when you’re stressed

The short-term stress response is not necessarily bad, because it prepares the body to cope with external challenges. For example, tadpoles that are exposed to dragonfly nymphs grow larger and have bigger tail fins than other tadpoles.

However, chronic stress over a long time can seriously affect an animal’s health (humans included) and survival rates.

How do koalas respond to stress?

Koalas release the stress hormone cortisol in response to any unpleasant stimulus like being handled by humans (oddly, males are much more stressed by handling than females, unless the females are lactating).

Koalas have biological feedback mechanisms that can regulate the amount of cortisol they produce, so they can carry on with their day-to-day routine. However, if koalas are continuously stressed by something large and permanent, such as land clearing of their territory, it’s difficult for them to relax from a stressed state.

When this happens, the body undergoes a barrage of sub-lethal chemical changes. The resulting chronic stress can negatively affect the animals’ reproductive hormones and immune system function.

Koalas, like all animals that call Australia home, have basic physiological and behavioural adaptations needed for life in Australia’s often extreme environment. But human-induced threats such as land clearing continue to create ecological imbalances, and chronic stress makes it very difficult for koalas to cope with environmental change.

How much stress can a koala bear?

As my review of the research shows, the most common sources of stress for koalas are heat stress, car impacts and dog attacks. Foetal development of koalas could also be impacted by maternal stress due to lack of adequate food from gum trees in drought periods.

Urban and fringe zones (areas between rural and urban zones) are particularly stressful for koalas, with added pressures like noise pollution and a higher chance of land clearing.

All of these factors create a continual strain on koala physiology. The sight of a koala dead by the road is the distressing culmination of multiple, complex and dynamic environmental influences.

Clinical research has shown that wild koalas are suffering from chronic stress. Koalas are often rescued with signs of trauma, caused by car accidents, burns or dog attacks, which is very difficult to handle in veterinary clinics.

Koalas are a living treasure, the only extant representative of the family Phascolarctidae. They live exclusively on Australia’s east coast, but are considered rare in New South Wales and South Australia.

There are now numerous local dedicated koala conservation centres aimed at safeguarding their habitat and educating the public. Koalas also help increase public awareness of conservation among both young people and adults.

But more research is needed in studying how they respond to the stresses of life in a human-dominated landscape. Techniques such as non-invasive hormone monitoring technology can be used to provide a rapid and reliable index of how our koalas are being affected by stress.

The ConversationSimply put, if land clearing is not reduced now we will continue to add invisible stress on koalas. Our children may one day be more likely to see a koala dead on the road than one happily cuddling their gum tree.

Edward Narayan, Senior Lecturer in Animal Science; Stress and Animal Welfare Biologist, Western Sydney University

This article was originally published on The Conversation. Read the original article.


A cull could help save koalas from chlamydia, if we allowed it

Desley Whisson, Deakin University

Whether it’s sharks, crocodiles or kangaroos, culling animals is always a contentious topic. But when the iconic koala is the species for which culling is being advocated, it sparks even more interest and debate.

Such was the case this week when researchers from Queensland and New South Wales published a study recommending that koalas be culled in the name of conservation.

Their proposal is for the selective culling of individual koalas suffering from chlamydia in an attempt to reverse the disease’s impact on vulnerable populations.

Koala chlamydia

Chlamydia is a sexually transmitted bacterial disease (a different strain to that which afflicts humans) that causes infertility and blindness in koalas, and is one of several factors thought to be behind the decline of koala populations in the eastern states. Koalas suffering the disease gradually become weak, stop eating, and die.

Although affected koalas sometimes may be found and taken into care, to date there have not been any systematic programs to combat the disease in wild populations. Given the negative effects of chlamydia on koala populations in some regions there is an urgent need to look at management options, including one that may seem quite radical – culling diseased individuals.

The current study considered a declining population on the “Koala Coast” of south-east Queensland. The researchers used computer simulations to model several disease management scenarios. The simulation that had the most positive effect on long-term population growth involved culling chlamydia-infected koalas that were already sterile and dying, and treating other infected koalas with antibiotics.

The study found that, to grow the Koala Coast population, around 10% (or 140 individuals) of koalas would need to be captured and culled or treated each year.

Killing for conservation

The idea of culling diseased individuals to manage disease and its impacts on wildlife populations is not new, and has met with both success (such as with Chronic Wasting Disease in deer in North America) and dismal failure (in the case Devil Facial Tumour Disease in Tasmanian Devils).

The effectiveness of these programs depends largely on the behaviour and ecology of the host species, and the distribution and nature of the disease. When enough is known about these aspects, computer modelling is useful for determining the potential effectiveness of a selective culling approach and for helping guide management actions.

But while modelling may inform us that culling is scientifically the best management approach, deciding whether and how to go ahead is complex, even more so when koalas are involved.

Koala management is closely scrutinised both nationally and internationally. The koala is the only native Australian species for which culling has been consistently dismissed as a management option (for overabundant populations in the southern states).

Although the current proposal for selectively culling diseased koalas isn’t “culling” as defined in the National Koala Conservation and Management Strategy, it still raises a question about killing koalas for conservation.

In 1997, culling was proposed as a component of an integrated strategy to manage high density populations of koalas on Kangaroo Island, South Australia. Despite having a sound scientific basis and the endorsement of many experts, it sparked much outrage and ultimately led to a decision at the Commonwealth level that culling will not be considered for management of koalas.

This decision has resulted in millions of dollars being spent on fertility control and translocation programs in Victoria and South Australia over the last two decades. These programs attempt to address situations where overpopulation of koalas is causing significant damage to local ecosystems.

Although some have brought positive outcomes after many years of intensive effort (for instance at Kangaroo Island and Mount Eccles in Victoria), these interventions are logistically challenging, extremely costly, and sometimes may have poor welfare outcomes for individual koalas.

Consequently, “do nothing” is the default management approach for many situations. But this can have drastic consequences for koalas, their habitats, and the other species that rely on those habitats.

Such was the case at Cape Otway in late 2013 when the Victorian government’s “do nothing” approach led to unsustainably high koala population densities, causing widespread defoliation of trees and the starvation of thousands of koalas. Around 700 koalas in irreversibly poor condition were killed when the government finally intervened on animal welfare grounds. Meanwhile, thousands of koalas likely suffered a slow death out-of-sight.

Although some trees recovered following the dramatic decline in koala numbers, high fertility has resulted in the population increasing again, and another imminent starvation event.

We do it for other animals, why not koalas?

Many wildlife researchers and managers would argue that a better approach for these situations would be to cull some koalas when it is clear that even more koalas will die if no action is taken.

This is not to suggest that culling be undertaken indiscriminately, nor in all situations. But it should be considered in circumstances where science indicates that it is the most effective approach to maintaining a healthy ecosystem and population of koalas.

It is the same approach that is used for numerous other native species in Australia and worldwide, so why shouldn’t it be considered for koalas, too?

Considering the outrage over killing Cape Otway’s starving koalas to reduce suffering, it seems that there may be little public support for culling koalas for any reason. It will be interesting to see how this new proposal to cull diseased koalas in Queensland and New South Wales will be received.

There likely will be opposition to culling and more support for a “treatment only” approach, despite its lower predicted effectiveness. However, one would hope that decision-makers place more weight on the scientific rigour of the research behind the proposal rather than the emotive argument that it is wrong to cull koalas.

The Conversation

Desley Whisson, Lecturer in Wildlife and Conservation Biology, School of Life and Environmental Sciences, Deakin University

This article was originally published on The Conversation. Read the original article.