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For approximately 22 km, the Snowy Mountains Highway travels along the border of a local national park. This stretch is a death trap for wombats crossing the road to get to the attractive grazing land which is on both sides of the road. |
| Erin Roger, who is completing a doctorate at the University of NSW, is involved in painstaking research with the aim of determining how wombats are managing to survive in the area, given the high road kill rates.
The first step was to establish base line data for the populations in the area. Erin used burrow surveys to determine which individuals were living where and which burrows were occupied.
All photos and figures from Erin Roger.
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Erin developed a habitat suitability map to establish where wombats were likely to be located. This was generated using environmental variables that were likely to predict where wombats would be in the landscape. Two of the variables are: Distance from forest because wombats prefer a mixed forest and open vegetation area - they use forested areas for their burrows and safety but prefer open grasslands for grazing. Slope because their burrows are often built on slope to prevent them from being flooded. The habitat suitability map indicated that the area close to the highway was very good habitat and that the landscape beyond this was quite marginal and suggested that the more optimal land adjacent to the highway was drawing the wombats in with a good mix of cover and grazing land.
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Below: Computer generated map using presence of burrows and environmental variables as predictors of wombat presence. The dark blue to pink areas on the figure are good habitat. These are areas where the most burrows were located and have environmental characteristics that wombats select for, such as a mix of forest and open grazing land and within proximity to drainage lines. The light blue and aqua coloured areas are more marginal habitat. Mostly characterised by heavy forests and poor drainage.
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The map also located source patches - locations where most wombats were located. While these were usually well away from the road, they have finite carrying capacity and so population density is important and as an area reaches its maximum carrying capacity, wombats are likely tor disperse from the site and possibly to the locations next to the highway. | | Interestingly it is the adult females who tend to disperse from an area. This seems to be a ploy by the mother to help her joey survive. Once the joey is weaned, the mother leaves the area and her joey has her territory and burrow, thus ensuring optimal survival for her offspring. While females are mainly dispersing, the road kill ratio is about gender equal, reflecting the much wider home ranges of males and their attraction to the females.
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The next step in the research will be to use GPS collars to find out when the wombats are crossing the road and where they are going. It is not known if the road kill is age related because wombats have rootless, evergrowing teeth, making it impossible to age an adult wombat. It is quite possible that the roadside population may be (for example) quite old - another factor that could contribute to an unexpected sudden decline in their numbers. The data for the habitat suitability map were used in a computer program to generate ‘a ‘patch map’ which showed where the subpopulations were in the landscape. Seven subpopulations were identified; two being roadside groups and a few acting as ‘source populations’. These are the populations from which wombats were likely to be dispersing to the roadside.
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The program was used to model the projected survival of the roadside groups. Setting the survival rate at the current rate (which is about 50% of the group annually) the model predicts that the roadside populations will be extinct within 50 years. The model also showed that dispersal from source groups was crucial for survival and if it should decease (say by 30%) the roadside groups will have disappeared within 15 years. |
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Figure above shows the annual mortality for wombats along the stretch of highway.
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There is little interest in the survival of the common wombat because the species is regarded as abundant. The threats to their survival are all introduced: road kill, foxes, sarcoptic mange and most importantly, loss of habitat. However without research and monitoring little is actually known about their true representation or their environmental importance. |
| They are superbly adapted to their environmental niche and can even survive bushfire, hiding in the safety of their underground burrows.
They occupy a wide environmental niche but little is known about their importance for maintaining a healthy ecosystem even though they are our only major burrow digger with extensive turnover of soil and they are wide ranging browsers who may be important in seed dispersal.
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The final phase of Erin Roger’s research will focus on the environmental credentials of wombats which may help raise community awareness of and interest in this poor cousin of the cuddly koala.
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