Targeted field testing of wildlife road-crossing structures: koalas and canopy rope-bridges
Goldingay, RL & Taylor, BD 2017, Australian Mammalogy, vol. 39, pp. 100-104.
Wildlife road-crossing structures aim to provide safe passage for wildlife movement and dispersal. A three-year targeted field test of canopy rope-bridges revealed that koalas did not utilise these structures to move between trees, instead travelling along the ground.
With the ever-expanding road networks in Australia, wildlife road-crossing structures have been installed in many places to minimise their impacts on native wildlife. Since different animals exhibit different dispersal and movement behaviours, they will require different traverse structure designs. It is therefore essential to monitor and evaluate the effectiveness of these traverse structures for the specific species that these structures are designed to target. The present study investigated the usage of four different designs of rope-crossings by koalas in Lismore, New South Wales, and found that none of the structures were used by koalas during the 2.9-year monitoring period. The authors attributed this finding to a mismatch between the ecology and behaviour of the koalas and the rope-bridges. The home ranges of koalas, in general, are quite large, and they can travel an average of 38 to 66 m a day. Koalas are also routine ground travellers and are highly mobile on ground. It was therefore apparent that the koalas did not need to utilise these structures to travel around. Furthermore, leaves of neighbouring trees often differ significantly in their concentration of formulated phloroglucinol compound (which influences feeding selection), thus trees connected by rope-bridges (to adjacent trees) may have been less attractive to koalas than other trees. Moreover, the design of some of the rope-bridges may have limited the koalas’ access to and across these structures, e.g. the 3-sided bridge that contained metal plates and multiple ropes that are difficult for koalas to climb.
As a result of their findings, the authors suggested the installation of wildlife underpasses and overpasses would be a more appropriate option to allow safe passage across road for the koalas.
Summarised by Cherie Chan
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