Seasonal oestrous cycle activity of captive female koalas in south-east Queensland
Ballantyne, K, Lisle, A, Mucci, A, Johnston, SD 2015, Australian Mammalogy, vol. 37, pp. 245-252.
Over a four-year period, 33 mature, captive female koalas were investigated regarding the seasonality of their oestrous behaviour, with the potential impacts of rainfall, temperature and photoperiod explored specifically. Findings revealed noticeable seasonality in behavioural oestrus, as well as a significant correlation between oestrous cycle activity and both average monthly temperature and photoperiod.
For the duration of the study, individuals were housed in single-sex enclosures. Oestrous detection involved the introduction of a ‘teaser’ male into each female enclosure, where he was permitted to urinate and vocalise. Females were deemed to be in oestrus if response behaviour encompassed ear flapping, jerking, homosexual mounting and bellowing. Strong seasonality in behaviour was displayed, with most koalas in oestrus between October and March. While oestrus behaviour was associated with mean monthly temperature and photoperiod, a more powerful relationship was observed when accounting for time of year (breeding versus non-breeding season). No significant relationship was identified between behaviour and rainfall. Data on mating occurrence and births indicate that, while breeding may take place throughout the year, mating is considerably more successful between November and April.
This study corroborates the existing literature, presenting clear seasonality in koala births, which aligns with an increased prevalence of oestrous expression. Months displaying highest oestrus behaviour were also those with increasing day-length, with a noticeable drop in this behaviour occurring in late Autumn and Winter. These findings thus indicate that day-length plays a potential role in commencing oestrous cycle activities. A similar trend was observed for temperature, where peak oestrous behaviour occurred during months of warmer temperatures. This can be explained as warmer conditions allow individuals to focus on reproductive activities, with energy previously required for thermoregulation reallocated. It is likely that, because individuals were captive and food was not a limited resource, the influence of rainfall on oestrous seasonality did not manifest. Alternate findings are likely to have been observed in wild populations, where quality of food resources is heavily dependent on annual rainfall.
The koala breeding patterns identified in this study are clearly affected by seasonality, with factors such as temperature and photoperiod influencing the commencement of oestrous behaviour. Future climate change scenarios are thus likely to impact the timing of the koala breeding season and as such, the combined effect of environmental factors (including temperature and rainfall) requires further investigation.
Summarised by Julian Radford-Smith
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