The end of the line? Sandalwood surveying on Bon Bon Reserve
For National Tree Day, Richard McLellan takes us into the South Australian outback for a sandalwood survey, exploring the significance of the species and its unfortunate plight.
Insights into diet, health and density of arid zone wombats on Bon Bon Station Reserve
Bon Bon Station Reserve is home to what is believed to be the northern most population of Southern Hairy-nosed Wombats. This population also holds the distinction of existing in one of the lowest rainfall zones across the species’ distribution, recording an average of just 150 mm annually.
Although wombats live in semi-arid and arid zones, droughts are their biggest killer and a significant threat to the species’ long-term persistence.
As drought events are predicted to increase in severity, frequency, and duration in the future, studying wombats living in different rainfall zones is important to understand how wombats, and indeed other marsupials living in these environments, are impacted by drought, and how they may adapt to drier conditions.
Researching the answers to these questions is the basis of my PhD project. One aim of this research is to understand how the diet of Southern Hairy-nosed Wombats changes in different rainfall zones across their distribution and how this relates to the diversity of the gut microbiome of animals within the same study populations.
This is important as the microorganisms in the gut are responsible for extracting vital nutrients and energy from the diet that wombats can’t extract themselves. This is particularly important for wombats in regions with low rainfall where vegetation may be scarce and of poor quality, as found on Bon Bon Station Reserve. Not only can the diversity of the gut microbiome inform us about what vegetation wombats can digest, but it can also be used as an indicator of health.
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Preserving microbiome samples Photo David Taggart
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Burrows overlooking a salt lake Photo David Taggart
Remarkably, both the diet and the gut microbiome of an animal can be characterised through DNA found in scats.
With this in mind, Dr David Taggart and I headed to Bon Bon Station Reserve in November 2021. To get an accurate picture of the wombat gut microbiome, fresh scats were collected. This meant visiting two field sites in the early mornings across three days to search around burrow entrances and nearby scratching posts for fresh samples.
Our first site was a sandy slope overlooking a picturesque salt-lake. After a few false starts getting lost following the tracks of a wandering wombat, taking some time getting our eye in spotting warrens, and watching a Mulga Snake slither down a burrow, we found the ten scat samples I needed from this site.
To avoid deterioration of the microbes within the scat due to time and temperature, and to prevent contamination from contact with soil, scats were preserved soon after collection. To do this, and in as sterile a manner as possible, the inside of the scats were scooped out and mixed with ethanol before being frozen. In the field this can be difficult, involving multiple changes of gloves and frequent sterilising of equipment with bleach and ethanol, all while hunched over in the dirt next to a car for some shade and protection from the wind.
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Wombat tracks in the sand Photo Shannon Kleemann
Along with the collection of scat samples, we also surveyed a subset of the warrens at Bon Bon to record warren characteristics including: soil type, diameter and the number of active and inactive burrows. This data can be used to help approximate wombat density at Bon Bon and along with other study sites in the state, paint a picture of how rainfall and soil type effects wombat abundance.
The next day took us to the rocky hills further north on the reserve. Here, the soil type and shrubs hid the burrows so well that searching by sight alone seemed impossible, and even with the use of a GPS warrens remained undetected until we were right on top of them.
To our dismay, even after extensive trekking to the most warren-dense areas, most burrows were not particularly active. Luckily, we had the third morning to visit both field sites to collect the extra samples I needed. It was good timing too, as the periodic rain that had started not long before our trip commenced, became heavier and caused the closure of many unsealed roads to our south and most of the tracks across the reserve.
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A Mulga snake cohabitating in a wombat burrow Photo Shannon Kleemann
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Warrens were hidden by rocky soils and shrubs Photo Shannon Kleemann
Now that I have my samples, the next step is to extract and sequence the microbial and plant DNA. These will be compared to a library of known DNA sequences to tell us what the wombats are eating and what microbes are helping them digest their food.
After a second collection period in Autumn, I’ll be able to compare the diet and gut microbiome of the wombats at Bon Bon across seasons, and to study sites on the Eyre Peninsula and in the Murraylands. This research not only addresses a knowledge gap in the species’ ecology across an important part of its range (Bon Bon Station Reserve), but will broaden our understanding of the impacts of changing rainfall and soil type on Southern Hairy-nosed Wombat diet and microbiome, and along with other data collected across my PhD, provide a basis to model the likely impacts of climate change on wombat health, breeding and survival into the future.
