Mention koalas and the image that comes to mind is that of a cuddly animal snoozing, whilst clinging on to a tree trunk for dear life - and rightfully so, given that the animals sleep for up to 20 hours a day! However, while the fact that their sedentary lifestyle is caused by their unusually small brains and the limited nutritional content of the eucalyptus leaves they consume is well-known, what was never questioned was their penchant for tree trunks. Turns out that the smart koalas have figured out that staying close to trees is the best way to beat the heat, during the hot Australian summers.
The surprising revelation was made by University of Melbourne ecologist, Michael Kearney and doctoral student Natalie Briscoe, who stumbled upon the discovery while conducting a study to investigate how the animals are able to survive the summer temperatures that often exceed 104°F (40°C).
The question was particularly relevant for the koalas given that the small marsupials do not drink any water and instead rely solely on the liquid present in the eucalyptus leaves they devour voraciously. While this is enough to sustain them during the cooler winter months, it could become an issue during the sweltering summers especially since climate change is expected to result in even more extreme temperatures.
The researchers began by placing radio collars on 37 koalas that reside on French Island in the state of Victoria, and tracking their movements during the winter of 2009 and then again during the peak summer months from December 2010 to March 2011. In addition to keeping detailed records of the movements of the collared animals, they also observed an additional 130 koalas that reside in the same region.
What they discovered was that the smart animals not only change their sleeping areas depending on the weather, but also, the trees they sleep on. During the summer, they gravitate toward the part of the tree trunk or branch that is closer to the ground. In winter, they happily perch higher up, spending a bulk of their time on outstretched branches. In addition, during the hottest days, many koalas appeared to find solace in Acacia trees, a fact the researchers found intriguing given that the animals do not eat the leaves.
To investigate the reason behind this deliberate behavior, the researchers used an infrared thermometer to measure the temperatures of four species of trees - three eucalyptus and one Acacia, during the hottest summer months. This revealed what the koalas have known all along - the tree trunks and the branches that are closer to the ground sport a much lower temperature than the surrounding air. Also, of the four measured, it was the Acacia tree trunks that were the coolest - by as much as 9°F!
This led Kearney and Briscoe to speculate that the koalas tree-hugging behavior was critical to their survival especially during the summer months. In order to verify their hunch, the researchers devised an equation to determine just how effective 'tree-hugging' could be. After taking their fur into account, they calculated that a 25-lbs koala was able to rid 68% of its excess heat on a 95°F day, by simply hugging a tree in a shady spot. Pretty cool!
The team who published their findings recently in the science journal, Biology Letters, believe that koalas aren't the only ones taking advantage of the phenomenon. They suggest that there is a whole microclimate in the shady trunks that is important for well-being of many animals, ranging from tree-dwelling primates to birds.
These new findings will go a long way in helping wildlife researchers trying to create special sanctuaries to protect the vulnerable koalas from the perils of climate change as well as loss of habitat. Now, in addition to the eucalyptus trees that are the marsupial's primary source of food, they will include a spattering of Acacia trees to ensure that they have access to natural air conditioning, should they need it.
Though often referred to as 'bears', koalas are not a member of the Ursidae family of mammals that conventional bears belong to. Rather, they are a species of marsupial. Found primarily in Australasia, the mammals are characterized by the pouch they carry their babies in. Koala offspring, which are the size of a small bee and blind when born, spend the first six months of their life nestled inside the mother's protective pocket and the next six, clinging on to her back or belly. Endemic to eastern Australia, the nocturnal animals depend solely on eucalyptus leaves for their survival, eating as much as 2.5-lbs a day and even storing some for snacks, inside the pouches of their cheeks. In fact, the animals eat so many of the leaves that they emit the distinct odor of eucalyptus oil that is strong enough to keep predators at bay!
Resources: nationalgeographic.com, news.yahoo.com, latimes.com