Behavioural Determination of Visual Function in the Koala (Phascolarctos cinereus)
Leisa M. schmidAB, Katrina L. Schmid and Brian Brown
School of Optometry, Queensland University of Technology, Brisbane, Qld 4001, Australia.
A To whom correspondence and reprint requests should be sent.
B Present address: Vision, Touch and Hearing Research Centre, Department of Physiology and Pharmacology, University of Queensland, Brisbane, Qld 4072, Australia
A behavioural estimate of the koala's dependence on vision was made using fabric hoods to degrade the vision of ten male koalas. Koalas were placed on the ground in a square enclosure, with a centrally placed 'tree'. With unobstructed vision, the koalas quickly travelled across the ground to the tree and climbed it. However, with severely reduced vision, the koalas would not search for or climb the tree. When their vision was obscured, the koalas tended to raise their forelegs when walking, taking high, reaching steps. The koala appears to require a certain minimum level of vision before climbing trees. Ocular chlamydial infection, which can cause a significant visual loss, may result in similar changes in behaviour and thus contribute to mortality.