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Using complementary remote detection methods for retrofitted eco-passages: a case study for monitoring individual koalas in south-east Queensland

Dexter, CE, Appleby, RG, Edgar, JP, Scott, J & Jones, DN 2016, Wildlife Research, vol. 43, no. 1, pp. 369-379.

This study employed a variety of techniques to monitor the use of infrastructure retrofitted to provide safe passage under or over roads by individual koalas. By doing so, researchers were able to better understand the roles that wildlife crossing structures might play in preventing wildlife-vehicle collisions and enhancing koala habitat and population connectivity.

  Six study sites were selected across south-east Queensland at which existing infrastructure had been retrofitted to provide passage for wildlife to cross roads. All koalas found within an area approximately 1.5km2 around each wildlife crossing structure were captured and fitted with a subcutaneous radio frequency identification (RFID) tag. These koalas were also marked with plastic ear tags for visual identification, which were later replaced by wireless identification (WID) ear tags. In combination with these technologies, other monitoring methods including GPS/VHF collars, camera traps, and sand plots were employed to monitor use of the eco-passages by koalas. The researchers required a road or structure crossing to be recorded by at least two monitoring methods to be verified. Fifteen tagged koalas were observed to complete 130 crossings over the 30-month monitoring period. Of these, 41 crossings using eco-passages were made by seven koalas. The other 89 crossings were completed by thirteen individuals, and these were either on the road surface, or the mode of passage could not be confirmed. It is interesting to note that road crossings, either on the road surface or using crossing structures, were undertaken by only a small subset (21%) of tagged koalas.

  Vehicle strikes are a significant source of mortality for koala populations. Additionally, roads can present barriers to the natural movements of koalas that can negatively affect dispersal and metapopulation dynamics. As a consequence, road mitigation structures such as fauna overpasses and underpasses have gained attention from governments and transport managers as strategies to maintain habitat connectivity in urbanised landscapes. Given the significant costs associated with these structures, however, it is important to understand the benefits that they are likely to provide for wildlife to ensure that mitigation is cost-effective. This study has built upon previous studies that record species’ presence in or on road crossing structures by documenting passage usage at the individual level, which is necessary for identifying the factors that may influence whether and how an animal uses a crossing structure.

  The authors of this study suggest that complementary monitoring techniques such as those employed here are ideal for capturing detailed data about the use of road crossing structures to make judgments about their effectiveness. Complementary monitoring methods not only provide information about the movements of specific individuals of interest within a population but importantly generate both broad- and fine-scale data that can assist in understanding the role of wildlife crossing structures at both the individual and landscape level.

 

Summarised by Joanna Horsfall

 

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