Designing a devil road grid – A practical challenge for engineers and biologists
A key aim of the Save the Tasmanian Devil Program is to maintain the devil population in the wild and the best way to stop the spread of the facial tumour disease is to prevent diseased devils coming into contact with healthy ones. A primary management strategy for the Program, therefore involves isolating large areas of natural landscape so as to keep healthy devils separated from diseased devils – in the wild.
Keeping unwanted devils out is not so difficult if the area is naturally disconnected like Maria Island, but it’s more challenging in the case of isolation areas on the Tasmanian mainland. Hence, the Program is looking at a range of strategies to prevent devil movement into landscape isolation areas including barrier fences, buffer zones, road grids, natural animal deterrents and trapping programs.
A particular investigation being undertaken at present is how to restrict devil movement along roads which intersect the isolation areas. Central to this is the design of a suitable road grid which restricts devils whilst enabling public road use. This is a challenging task, requiring professional engineering principles and specifications, combined with scientific knowledge of devil behaviour.
An experimental road grid was designed by local engineering firm, Pitt & Sherry and tested by the Program on devils in the semi-wild Free Range Enclosures. Video surveillance shows that although the grid was effective in over a third of the cases, devils are very determined, agile, strong and versatile animals when it came to crossing the experimental grid. They use their tails and chins like a fifth and sixth leg. They appear ambivalent to losing their footing, quite confidently just trying to find purchase in another manner. This ability, coupled with their going-forward type determination, makes the development of the grid very difficult.
A total of 639 videos of devils interacting with the grid were catalogued and scored according to the devils reactions. Of these, 34% of the encounters with the grid were devils which inspected it and then turned away, 31% of the encounters resulted in devils crossing the grid with relative ease, 16% of crossings were with difficulty and 5% of animals never crossed the grid.
These results are now being used to modify the road grid design and demonstrate the importance of combining a range of deterrent solutions for devil movement on roads. Previous trials of devil audio devices, for instance, have shown that the sounds of dogs barking make devils ‘nervous’, and the hisses and growls that devils make when warning each other of their presence, may also act as a deterrent.
These audio and visual deterrents will be trialled next in conjunction with a modified road grid for which the Program is seeking further engineering input. Interested engineers (or anyone who has an engineering brain and is a keen practical problem solver) who might be able to help with design improvements for the devil road grid, are asked to contact the Program. There are hours of video footage available to observe the devils response to the experimental road grid. A short compilation of some of this surveillance shows how the devils navigate the obstacle grid.