July 29th 2009
Island koalas' secrets studied
It has often been claimed that Magnetic Island's koala's are the most northerly population to be found in Australia. According to experts, recently researching Magnetic's koalas, however, this is not true. But, when it comes to actually seeing a wild koala this far north, then it might as well be. This also applies for the researchers who are trying to find out, among other things, and with climate change in mind, just how our koalas deal with heat and our harsh, late dry season and why the population appears to remain fairly stable without the booms and busts commonly experienced elsewhere.
The JCU team is headed by Associate Professor Andrew Krockenberger from the School of Marine and Tropical Biology (Cairns) who ran a field camp last week with zoology students at the Picnic Bay Recreation Centre.
One PhD student from Melbourne University with a particular interest in koalas was Natalie Briscoe who has studied koalas on French Island. This is her first time on Magnetic and, with the group, was catching, weighing and measuring koalas around Magnetic's famous Forts walk, where Island koalas appear most frequently.
“I'm interested in what maintains the koala population at this level. On other islands you see them boom and bust,” said Natalie.
The whole question is a rather open one and the team is interested to hear opinions from locals – particularly longer term residents with any observations of koala's in larger numbers than normal in times past.
Natalie has also been measuring factors such as wind speed and temperature on koala behaviour.
The team caught and released six koalas during the study period and are hoping to begin to understand just how far each koala ranges, what their territories are and what their densities are like.
Andrew Krockenberger says that koalas have been found as far north on the mainland as Shiptons Flat near Cooktown but, “They are very hard to find this far north.”
He also believes that our koala's are significantly smaller than those found in southern states. “Males grow up to 15kgs in the south but we found one that was about four years old at 7.5kgs,” he said, adding, “It might grow a bit more.”
Something that will be looked at in terms of climate and, ultimately, how koalas can deal with climate change, is changes fur density and other proportions. “We are modelling how much heat they are gaining in the sun relating to how much food they need to eat and their energy budgets.” said Andrew.
Just why the Magnetic koala population has seemingly remained so stable over the years is important to the team as population booms and the great difficulties of relocation at places like Kangaroo Island have been a sad feature of koala management.
Andrew has a hunch that it is, in fact, Magnetic's long and harsh dry season that keeps the koala population here from exploding.
“Natalie is looking in general at how climate affects them in the late dry. She's doing modelling on changes in climate patterns to predict effects in terms of distribution. Water is particularly important,” say Andrew. Over-heated koalas deal with the higher temperature by panting and licking their arms which leads to water loss.
Andrew is something of a koalapaedia and is happy to tackle popular koala misconceptions. If you believe, for instance, that koalas gain all their moisture from gum leaves and don't drink, then think again. During the heat wave and devastating bush fires in Victoria this year koalas were being revived and drinking directly from water containers. Andrew believes they probably drink dew from leaves as well.
And while their preferred food is leaves from our steely-trunked blue gums (Eucalyptus tereticornis) and narrow-leafed iron bark (Eucalyptus creba), Andrew says that Koalas have been documented eating paperbarks and even radiata pines, “but not in huge proportions.”
Andrew thinks that our dry season is, “crunch time for the eco-system,”
“The harsh late dry may slow down youngsters and the newly weaned or females don't manage to raise babies,” says Andrew. But he acknowledges other factors such as diseases like chlamydia (known to be a problem for Island koalas) and even leukemia, which he is aware of from “very anecdotal” reports.
Magnetic Times found this koala crossing the West Point
track last week and noticed its arms, legs and underbelly
were wet. It had come from the mangroves!
Yet another factor - which relates to the Magnetic Island koalas not actually being native to Magnetic but introduced in the 1930s - is the “founder effect” by which the first koalas may have had a genetic condition which has affected reproduction rates. Predation from dogs is another factor as is that from large pythons as well as fires. Large pythons are however very rare on Magnetic and although Magnetic Times has reported occasional and viscious dog attacks on koalas it seems unlikely they are keeping a booming population at bay. As for fire, Andrew says, “My gut feeling is that if many koalas are getting burned people would know about it.”
It seems that koalas grow to different ages in different places. According to Andrew, Twenty years is pretty old in some populations while twelve is old in northern NSW. Nobody knows how long the Magnetic koalas live for and determining the age of the animals is difficult with living animals. Tooth wear is one, not very accurate method. The best age indicator is “growth rings” which can be found in the “cementum” around the roots of koalas' teeth. Not to be tried on living animals, Andrew is however particularly keen to check on dead koalas and is urging locals who come across road-killed koalas to pass on their location or take the bodies to the QPWS rangers' Office in Picnic Bay (Ph: 47785378).
It seems like the most important terrestrial animal to Magnetic Island's tourist appeal are more mysterious than we might think. But the work of Andrew and Natalie, which will see them returning periodically to Magnetic, may slowly help us understand and better look after our fluffy Island icons in a time when the need for knowledge to mitigate climate change and other threats has never been greater.
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