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Behaviour & communication

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.

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Discrimination of sex and reproductive state in koalas, Phascolarctos cinereus, using chemical cues in urine

Charlton, BD 2014, Animal Behaviour, vol. 91, no. 1, pp. 119-125.

Koalas can determine both the sex and oestrous stage of other individuals by detecting unique chemical cues in their urine. During their breeding season, male and oestrus female koalas at Lone Pine Koala Sanctuary demonstrated a higher interest in the urine of males than did nonoestrus females, which avoided male urine. Male koalas investigated the urine of an oestrus female, but not that of a nonoestrus female.

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Disentangling the mechanisms of mate choice in a captive koala population

Brandies, PA , Grueber, CE, Ivy, JA, Hogg,  CJ & Belov, K 2017, PeerJ Preprints (Not Peer Reviewed).

Successful captive breeding is a major contributor to the conservation of many threatened species; however, the sustainability of several captive breeding programs is limited by pair incompatibility. If captive breeding is to be both successful and sustainable, an understanding of the behavioral and genetic drivers of pair incompatibility is essential.  To determine what behavioral and genetic drivers influence pair incompatibility of captive koalas, analyses of 28 years of pairing data from the studbook for the San Diego Zoo koala colony and genetic analyses of 70 banked koala DNA samples from the same colony were performed. Both behavioral and genetic determinants were found to contribute to captive koala mating success.

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Estimating the active space of male koala bellows: propagation of cues to size and identity in a Eucalyptus forest

Charlton, BD, Reby, D, Ellis, WAH, Brumm, J & Tecumseh Fitch, W 2012, PLoS ONE, vol. 7, no. 9, e45420.

The acoustic cues that most reliably distinguish the bellow of one male koala from another can be transmitted across a distance of up to 50 metres in a eucalypt forest. The acoustic features that indicate the size of a male, however, can be reliably communicated over a longer distance of up to 150 metres in the typical habitat of the koala.

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Female koalas prefer bellows in which lower formants indicate larger males

Charlton, BD, Ellis, WAH, Brumm, J, Nilsson, K & Fitch, WT 2012, Animal Behaviour, vol. 84, no. 1, pp 1565-1571.

Formants, the frequencies produced by vibrating air in the vocal tract, are acoustic cues that female koalas can use to evaluate the size of a bellowing male. Oestrus female koalas at Lone Pine Koala Sanctuary looked significantly more towards and spent significantly more time in close proximity to speakers broadcasting bellows with lower formant values, indicating a large male caller, than to speakers broadcasting higher formant values produced by a smaller male.

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Free-ranging male koalas use size-related variation in formant frequencies to assess rival males

Charlton, BD, Whisson, DA & Reby, D 2013, PLoS ONE, vol. 8, no. 7, e70279.

Male koalas detect acoustic cues in the bellows of their competitors to the caller’s body size and change their own vocal response accordingly. When exposed to a bellow from a large, as opposed to a small, caller during the breeding season, male koalas produce a delayed bellow of greater duration.

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Heterosexual and homosexual behaviour and vocalisations in captive female koalas (Phascolarctos cinereus)

Feige, S, Nilsson, K, Phillips, CJC & Johnston, SD 2007. Applied Animal Behaviour Science, vol. 103, no. 1, pp 131-145.

Female koalas in captive environments engage in both homosexual and heterosexual interactions, although only heterosexual interactions have been recorded in nature. In captivity, female koalas also produce acoustic bellows, a sexual behaviour typically only observed in males. This study of koalas in Lone Pine Koala Sanctuary revealed that homosexual interactions between females comprised the same component behaviours and vocalisations as, but were shorter in duration than, heterosexual interactions.

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Perception of male caller identity in koalas (Phascolarctos cinereus): acoustic analysis and playback experiments

Charlton, BD, Ellis, WAH, McKinnon, AJ, Brumm, J, Nilsson, K & Tecumseh Fitch, W 2011, PLoS ONE, vol. 6, no. 5, e20329.

The bellow of a male koala is unique from that of other koalas to the extent that bellows can be consistently discriminated between and identified to individuals. Both male and female koalas that were familiar with the bellow of a particular male dishabituated in response to the bellow of an unfamiliar male and displayed comparatively greater interest in the novel stimulus.

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Perception of size-related formant information in male koalas (Phascolarctos cinereus)

Charlton, BD, Ellis, WAH, Larkin, R & Tecumseh Fitch, W 2012, Animal Cognition, vol. 15, no. 1, pp. 999-1006.

This report is the first to document evidence of male koalas being able to perceive variations in formant spacing in the bellows of other males that convey the caller’s body size.

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Subharmonics increase the auditory impact of female koala rejection calls

Charlton, BD, Watchorn, DJ & Whisson, DA 2017, Ethology, vol. 123, no. 1, pp. 571-579.

Subharmonics in female koala vocalisations made when rejecting a mating attempt create an unpredictable acoustic pattern that may serve to attract a higher-quality mate.

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The acoustic structure and information content of female koala vocal signals

Charlton, BD 2015, PLoS ONE, vol. 10, no. 10, e0138670.

Female koalas produce distinct categories of vocalisations that differ in acoustic structure. Some of these vocalisations contain acoustic cues to the caller’s identity, age and sex, which is likely of great adaptive significance to male koalas.

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The association of tooth wear with sociality of free-ranging male koalas (Phascolarctos cinereus Goldfuss)

Logan, M & Sanson, GD 2002, Australian Journal of Zoology, vol. 50, no. 1, pp. 621–626.

This study found that tooth wear is associated with the reproductive efforts of male koalas. Koalas with very low and high tooth wear were found to have decreased reproductive efforts, while koalas with intermediate tooth wear were found to exert higher reproductive effort.

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The effects of tooth wear on the activity patterns of free-ranging koalas (Phascolarctos cinereus Goldfuss)

Logan, M & Sanson, GD 2002, Australian Journal of Zoology, vol. 50, pp. 281–292.

This study found that increased tooth wear affects adult koalas in multiple ways. Koalas with significant tooth wear spend less time sleeping and being inactive than those without. They also spend less time moving about and stay within smaller areas. On the other hand, they spend more time feeding and have more spaced out feeding times, thus becoming less nocturnal.

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Tree-hugging behavior beats the heat 

Briscoe, NJ 2015, Temperature, vol. 2, no. 1, pp. 33-35. 

  

  Koalas change their behaviour to use temperature variation in microclimates to cool themselves down by hugging cool tree surfaces during hot weather to increase heat loss. They were observed to minimise evaporative water loss through spending more time in shaded areas and hugging trunks of trees of the species Acacia mernsii, which has a cool trunk temperature.

 

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