Failure to Respond to Food Resource Decline Has Catastrophic Consequences for Koalas in a High-Density Population in Southern Australia

Whisson, Desley A.; Dixon, Victoria; Taylor, Megan L.; Melzer, Alistair

doi:10.1371/journal.pone.0144348

Cited by 43 publications

(45 citation statements)

References 25 publications

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“…A total of 10 adult male koalas served as subjects in the playback experiments. Individual males were identified using a combination of very‐high‐frequency (VHF) radio collars and ear tags (Sirtrack Pty Ltd, Havelock North, New Zealand) (sensu Whisson, Dixon, Taylor, & Melzer, ). The study site was a 5.5‐hectare manna gum ( E. viminalis ) woodland with a total population density of 7.3 adult koalas per hectare (October 2015 estimate).…”

Section: Methodsmentioning

confidence: 99%

Subharmonics increase the auditory impact of female koala rejection calls

2017

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Although non‐linear phenomena are common in human and non‐human animal vocalisations, their functional relevance remains poorly understood. One theory posits that non‐linear phenomena generate unpredictability in vocalisations, which increases the auditory impact of vocal signals, and makes animals less likely to habituate to call repetition. Female koalas (Phascolarctos cinereus) produce vocal signals when they reject male copulation attempts that contain relatively high levels of non‐linear phenomena, and thus may function as attention grabbing vocal signals during the breeding season. To test this hypothesis, we used playback experiments: firstly, to determine whether female rejection calls induce heightened behavioural responses in free‐ranging male koalas during the breeding season, and secondly, to examine how the relative amount of non‐linear phenomena in rejection calls influences male behavioural response. The results show that male koalas look for longer towards speakers broadcasting playback sequences of male bellows followed by a series of female rejection calls than those broadcasting only male bellows. In addition, female rejection call sequences with more subharmonics, higher harmonics‐to‐noise ratios, and less biphonation produced the greatest male looking responses. Our findings support the hypothesis that female koala rejection calls function to grab male attention during the breeding season, and indicate that subharmonics are the main acoustic feature that increases the auditory impact of these vocal signals.

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Section: Methodsmentioning

confidence: 99%

Subharmonics increase the auditory impact of female koala rejection calls

2017

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“…1). Population density of both the Raymond Island and Cape Otway koala populations is considered to be high (Menkhorst 2008;Whisson et al 2016).…”

Section: Sample Collection 25mentioning

confidence: 99%

Using non-invasive sampling methods to determine the prevalence and distribution of Chlamydia pecorum and koala retrovirus in a remnant koala population with conservation importance

et al. 2018

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Context. Pathogenic infections are an important consideration for the conservation of native species, but obtaining such data from wild populations can be expensive and difficult. Two pathogens have been implicated in the decline of some koala (Phascolarctos cinereus) populations: urogenital infection with Chlamydia pecorum and koala retrovirus 5 subgroup A (KoRV-A). Pathogen data for a wild koala population of conservation importance in South Gippsland, Victoria are essentially absent.Aims. This study uses non-invasive sampling of koala scats to provide prevalence and genotype data for C. pecorum and KoRV-A in the South Gippsland koala population, and compares pathogen prevalence between wild koalas and koalas in rescue shelters. 10 Methods. C. pecorum and KoRV-A provirus were detected by PCR of DNA isolated from scats collected in the field. Pathogen genetic variation was investigated using DNA sequencing of the C. pecorum ompA and KoRV-A env genes.Key results. C. pecorum and KoRV-A were detected in 61% and 27% of wild South Gippsland individuals tested, respectively. KoRV-A infection tended to be higher in shelter koalas compared with wild koalas. In contrast with other Victorian koala populations sampled, greater pathogen diversity was present in South Gippsland. 15 Conclusions. In the South Gippsland koala population, C. pecorum is widespread and common whereas KoRV appears less prevalent than previously thought. Further work exploring the dynamics of these pathogens in South Gippsland koalas is warranted and may help inform future conservation strategies for this important population.Implications. Non-invasive genetic sampling from scats is a powerful method for obtaining data regarding pathogen prevalence and diversity in wildlife. The use of non-invasive methods for the study of pathogens may help fill research 20 gaps in a way that would be difficult or expensive to achieve using traditional methods.

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“…We use the term “overabundant” here to describe a koala population that occurs at a density that results in defoliation of preferred food trees. If unmanaged, this can lead to widespread tree death, nutritional stress in the koala population, and even death of koalas due to starvation (e.g., Martin, , , ; Whisson et al, ; Figure ). Overabundance can occur where there are only two koalas per hectare (Menkhorst, ), but higher densities are typical.…”

Section: Where Does Koala “Overabundance” Occur?mentioning

confidence: 99%

“…On one hand, the koala is portrayed as a species that will be extinct by 2050 (Australian Koala Foundation, ); yet this is countered by reports of koala “overabundance” from the southern states, with calls to cull, sterilize, or translocate koalas to reduce high‐density populations (Natural Resources Committee, South Australia, ; Possingham et al, ; South Australian Government, ). In some cases, high‐density populations have caused complete and widespread canopy defoliation resulting in mass starvation of koalas (Menkhorst, ; Whisson, Dixon, Taylor, & Melzer, ). Although koalas in southern states are not listed as “vulnerable” under National legislation, nor listed in any special conservation category under state legislation, their management is considered differently to other common native wildlife.…”

Section: Introductionmentioning

confidence: 99%

“…South Australian and Victorian state governments abide by national policy to reject culling of “overabundant” koalas (Australian and New Zealand Environment and Conservation Council, ; DELWP, ; South Australian Government, ). Management of overabundant koala populations therefore relies on translocation and fertility control measures that are expensive and may have poor welfare outcomes for koalas (Duka & Masters, ; Whisson et al, ; Whisson, Holland, & Carlyon, ). Furthermore, implementing such measures over large spatial scales where there may be thousands of koalas is logistically difficult and economically not feasible.…”

Section: Introductionmentioning

confidence: 99%

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When an iconic native animal is overabundant: The koala in southern Australia

Whisson

Ashman

2020

Conservat Sci and Prac

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Management of overabundant native species is challenging at the best of times but is even more so when it involves an iconic species that is threatened in part of its range. Here, we examine koala overabundance, a situation that arises in some locations within the species' southern range. We consider the variable conservation status of the koala throughout its range, discuss where and why overabundance occurs, and its consequences. Programs to manage koala overabundance and impacts are generally ineffective, relying on costly and slow acting fertility control and translocation, and implemented only when a crisis already has occurred. A change in management approach is needed. Decisions should be based on an evidence-based and transparent decisionmaking framework that involves predicting where overabundance is likely, where damage costs will be high, and where proactive management is likely to be effective. With more than 65% of Australia's koala population occurring in the south and declining northern populations, a more considered approach to managing southern koalas for conservation of the species is needed.

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Failure to Respond to Food Resource Decline Has Catastrophic Consequences for Koalas in a High-Density Population in Southern Australia

Cited by 43 publications

References 25 publications

Subharmonics increase the auditory impact of female koala rejection calls

Subharmonics increase the auditory impact of female koala rejection calls

Using non-invasive sampling methods to determine the prevalence and distribution of Chlamydia pecorum and koala retrovirus in a remnant koala population with conservation importance

When an iconic native animal is overabundant: The koala in southern Australia

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