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Threatening processes

A survey of koala road kills in New South Wales

Canfield, PJ 1991, Journal of Wildlife Diseases, vol. 27, no. 4, pp. 657-660.

With increasing fragmentation of remnant forest along Australia’s east coast, motor vehicle accidents have become a significant cause of injury and death in koala populations. In a survey of koala road kills conducted in the northern coast of New South Wales between 1984 and 1990, 75 koalas were found to have died from injuries relating to motor vehicle accidents. After analysis, it was identified that healthy, young to middle-aged male koalas were more prone to vehicular incidents, especially during the mating period.

Assessing the significance of endemic disease in conservation – koalas, chlamydia, and koala retrovirus as a case study

McCallum, H, Kerlin, DH, Ellis, W & Carrick, F 2017, Conservation Letters, e12425.

The value of disease management as a tool for biological conservation is often contested. The koala presents an ideal case study for examining this debate. Endemic diseases, most notably chlamydiosis and koala retrovirus (KoRV), are highly prevalent throughout koala populations. The extent to which disease contributes to population decline, however, is not agreed upon.

Aversive behaviour by koalas (Phascolarctos cinereus) during the course of a music festival in northern New South Wales, Australia

Phillips, S 2016, Australian Mammalogy, vol. 38, pp. 158-163.

By monitoring changes in movement and behaviour of a resident koala population, this study investigated the extent of disturbance caused by a five-day musical festival in northern New South Wales. Seven koalas were monitored over a period of 6 months, whereby three koalas demonstrated extreme aversive behaviour in response to the festival, evacuating their known ranging areas. Three other koalas displayed aversive responses, but remained within known ranging areas.

Bearing up well? Understanding the past, present and future of Australia's koalas

Black, KH, Price, GJ, Archer, M & Hand, SJ 2014, Gondwana Research, vol. 25, pp. 1186-1201.

Evidence from fossil records of the family Phascolarctidae indicates that these specialist folivores, of which the modern koala Phascolarctos cinereus is the last surviving member, are particularly sensitive to climate change. Knowledge about the nature and rate of change in previous palaeocommunities of phascolarctids together with data relating to the responses of modern koala populations to historic climatic extremes indicate that the future survival of the species is under threat.

Behavioural determination of visual function in the koala (Phascolarctos cinereus)

Schmid, LM, Schmid, KL & Brown, B 1991, Wildlife Research, vol. 18, no. 3, pp. 367-374.

Reduction of vision in koalas was found here to result in significant behavioural changes. Maintaining a minimum level of vision appears necessary for koalas to be able to locate and climb trees, as with severely obstructed vision, captive koalas were not able to reach or climb a nearby tree.

Conserving koalas: A review of the contrasting regional trends, outlooks and policy challenges

McAlpine, C, Lunney, D, Melzer, A, Menkhorst, P, Phillips, S, Phalen, D, Ellis, W, Foley, W, Baxter, G, de Villiers, D, Kavanagh, R, Adams-Hosking, C, Todd, C, Whisson, D, Molsher, R, Walter, M, Lawler, I & Close, R 2015, Biological Conservation, vol. 192, pp. 226-236.

The koala has suffered a 50% decline in its distribution since European colonisation began in Australia, and consequently its conservation has become a national priority. The purpose of this review was to synthesise current knowledge of koala populations and their threats to identify a way forward for their conservation.

Consistent patterns of vehicle collision risk for six mammal species

Visintin, C, van der Ree, R & McCarthy, MA 2017, Journal of Environmental Management, vol. 201, no. 1, pp. 397-406.

The authors of this study developed a quantitative risk model framework for evaluating the extent to which the variables of species occurrence, road speed and traffic volume influence the risk of wildlife-vehicle collision for a section of road. The framework was applied to examine the risk of wildlife-vehicle collisions on Victorian roads for six species including the koala.

Decline causes of koalas in south east Queensland, Australia: a 17-year retrospective study of mortality and morbidity

Gonzalez-Astudillo, V, Allavena, R, McKinnon, A, Larkin, R & Henning, J 2017, Scientific Reports, vol. 7, 42587.

South-east Queensland koala populations have been in decline for several decades. The authors of this study examined a comprehensive database of 20,250 koala admissions into wildlife hospitals in the region between 1997 and 2013 to identify the causes of morbidity and mortality that have contributed to this decline. The results suggest that chlamydiosis, motor vehicle trauma and wasting are the most frequent conditions observed and that they frequently co-occur within individuals.

Decline of the urban koala (Phascolarctos cinereus) population in Warringah Shire, Sydney

Smith, P & Smith J 1990, Australian Zoologist, vol. 26, nos. 3-4, pp. 109-129.

Koala populations within Warringah Shire, Sydney have rapidly declined over the last 50 years. Initial declines can be attributed to habitat loss, as primary koala habitat was converted to urban area from the 1970s onwards. Surviving populations are now restricted to two main areas: Barrenjoey Peninsula and Ku-ring-gai Chase National Park, with only rare sightings in other areas of the Shire.

Failure to respond to food resource decline has catastrophic consequences for koalas in a high-density population in southern Australia

Whisson, DA, Dixon, V, Taylor, ML & Melzer, A 2016, PLoS One, vol. 11, no. 1, pp. 1-12.

Between September 2011 and November 2013, the growth and consequent collapse of a koala population resulting from a decline in key food trees was documented. During the study, population density grew from 10.1 to 18.4 koalas/ha, with a significant decline in manna gum (Eucalyptus viminalis) canopy condition taking place as a consequence of high browsing pressure. Individuals were shown to remain in small home ranges (0.4-1.2ha), regardless of the severity of food tree defoliation.

Foxes in trees: a threat for Australian arboreal fauna?

Mella, VSA, McArthur, C, Frend, R & Crowther, M 2018, Australian Mammalogy, vol. 40, no. 1, pp. 103-105.

For the first time in Australia, researchers have observed red foxes (Vulpes vulpes) climbing trees. It is not yet known whether such behaviour is common or if red foxes can prey upon arboreal species; however, this surprising behaviour may have negative consequences for koalas.

Individuals matter: predicting koala road crossing behaviour in south-east Queensland

Dexter, CE, Appleby, RG, Scott, J, Edgar, JP & Jones, DN 2018, Australian Mammalogy, vol. 40, no. 1, pp. 67-75.

An investigation into the factors influencing the movements of koalas has revealed that, within a population, not all koalas are equally likely to cross a road. Road mitigation strategies that target those individuals most at risk of vehicle strike are likely to deliver greater benefits for koalas than strategies that do not account for these inter-individual differences.

Modelling climate-change-induced shifts in the distribution of the koala

Adams-Hosking, C, Grantham, HS, Rhodes, JR, McAlpine, C & Moss, PT 2011, Wildlife Research, vol. 38, pp. 122-130.

Climate change is resulting in shifting distributions of koala populations throughout Australia as a direct result of increased temperatures and decreased rainfall. Bioclimatic models based on current koala localities and several climate change scenarios were used in this study to predict future climatic envelopes of koala populations. Results showed a likely progressive movement eastwards and southwards in Queensland, New South Wales and Victoria.

Modelling mammalian extinction and forecasting recovery: koalas at Iluka (NSW, Australia)

Lunney, D, O’Neill, L, Matthews, A & Sherwin, WB 2002, Biological Conservation, vol. 106, pp. 101-113.

The authors of this study modelled the effects of several population-boosting scenarios to evaluate the factors likely to be most important in the extinction and recovery of the koala population at Iluka, New South Wales. Improvements in neither mortality nor fertility rates reversed extinction risk. Only metapopulation planning to facilitate immigration into the koala population combined with increased fertility was found to restore the population to its initial size.

Morbidity and Mortality in the Koala (Phascolarctos cinereus)

Backhouse, TC & Bolliger, A 1961, Australian Journal of Zoology, vol. 9, no.1, pp. 24-37.

Of 28 koalas autopsied in 1960, pneumonia was the leading cause of death in this mortality study, which also presented as a comorbidity with trauma. Other significant causes of death were hepatitis, yeast infections of the species Cryptococcus neoformans, leukaemia and anaemia. Ovarian cysts were observed in a number of the koalas, but it was only the cause of death for koalas whose cysts had become infected. Finally, senility-associated diseases such as cardiac failure were seen at a low level.

Post-fire survival and reproduction of rehabilitated and unburnt koalas

Lunney, D, Gresser, SM, Mahon, PS & Matthews, A 2004, Biological Conservation, vol. 120, pp. 567-575.

Comparisons of koalas rehabilitated after sustaining burn injuries following a fire event against uninjured koalas found no significant difference in post-release survival and reproductive success between the two groups, indicating human intervention and rehabilitation efforts can be beneficial to conservation efforts following fire.

Skeletal fluorosis in marsupials: a comparison of bone lesions in six species from an Australian industrial site

Death, C, Coulson, G, Kierdorf, U, Kierdorf, H, Ploeg, R, Firestone, SM, Dohoo, I & Hufschmid, J 2017, Science of the Total Environment, vol. 584-585, no. 1, pp. 1198-1211.

Koalas and other marsupials living in high-fluoride environments are at risk of developing skeletal fluorosis. The severity of skeletal lesions in an affected animal is positively associated with bone fluoride levels. Of the six species studied here, all exhibited either localised or generalised periosteal hyperostosis but the distribution of lesions varied according to the animal’s mastication and gait.

The causes and prognoses of different types of fractures in wild koalas submitted to wildlife hospitals

Henning, J, Hannon, C, McKinnon, A, Larkin, R & Allavena, R 2015, Preventative Veterinary Medicine, vol. 122, pp. 371-378.

Fractures, whether caused by cars, dog attacks or falls from trees, regularly result in the death or euthanasia of wild koalas. It is, therefore, important for koala conservation and management to identify patterns and risk factors regarding the prevalence of fractures. Within this study, data collected from over 2000 wild koalas with fractures admitted to south-east Queensland wildlife hospitals were analysed. Head fractures and vehicle collisions were the most common type and cause of fractures respectively.

Time-delayed influence of urban landscape change on the susceptibility of koalas to chlamydiosis

McAlpine, C, Brearley, G, Rhodes, J, Bradley, A, Baxter, G, Seabrook, L, Lunney, D, Liu, Y, Cottin, M, Smith, AG & Timms, P 2017, Landscape Ecology, vol. 32, no. 3, pp. 1-17.

The effects of changes in landscape or climate on the prevalence of chlamydiosis in koalas may not manifest until several years after the initial change occurred. Disease prevalence and body condition of koalas in southeast Queensland were quantified to determine both the spatial factors that affect these variables and the time delay, if any, of the effect. For landscapes in which the area of suitable habitat increased, koalas had high body condition scores but also high disease prevalence three years later. Alternatively, when the extent of urbanisation in a landscape increased, koala populations exhibited an increased prevalence of chlamydiosis four years later and decreased body condition one year later. An increase in annual rainfall was associated with immediately improved body condition and reduced disease prevalence after two years.

Tree use by koalas (Phascolarctos cinereus) after fire in remnant coastal forest

Matthews, A, Lunney, D, Gresser, S & Maitz, W 2007, Wildlife Research, vol. 34, pp. 84-93.

Resource depletion as a result of wildfire has a short-term impact on koala populations in remnant forests. The present study revealed that koala populations at Port Stephens in New South Wales returned to utilising burnt trees shortly after intense wildfires that occurred in 1994, and some koalas were even observed using burnt trees exclusively. Furthermore, the authors noticed differences in the preferences and uses of tree species between the sexes, breeding and non-breeding females, day time and night time, as well as between seasons.