Recently I had the amazing opportunity to visit Yookamurra Sanctuary as part of the Ecological Society of Australia conference in Adelaide. Yookamurra is a 5000 ha reserve about 2 hours north-east of Adelaide, which is owned and managed by Australian Wildlife Conservancy. Within the property is a 1100 ha area surrounded by a predator-proof fence, which protects reintroduced populations of Boodies or Burrowing Bettongs (Bettongia lesueur), Woylies or Brush-tailed Bettongs (Bettongia penicillata), Numbats (Myrmecobius fasciatus), Bilbies (Macrotis lagotis), Bush-stone Curlews (Burhinus grallarius), and many other native species such as Southern Hairy-nosed Wombats (Lasiorhinus latifrons) and Malleefowl (Leipoa ocellata).
We arrived at Yookamurra in the late afternoon on a sweltering 39 degree day. After settling into our dongas, Yookamurra’s ecologist Noel Riessen took us for a walk through some of the old growth Mallee. The property contains one of the largest areas of intact old growth Mallee in Australia, and some of the trees on the property may be well over 600 years old. This means that fire was probably quite rare, even before European settlement, so fire management is very important to protect this ecosystem.
While there was very little animal activity in the heat of the day, the evidence of their nocturnal foraging was obvious. The ground was littered with diggings of many shapes and sizes, some freshly dug and some gradually filling in with litter and soil. This is what I came to see – it was very exciting for me to see the effects of digging animals in an arid ecosystem, and compare it with my own research on eastern bettongs in temperate grassy woodland. Like eastern bettongs, truffles make up a large part of the diet of Boodies and Woylies, and they turn over large volumes of soil in the process of finding them. Interestingly, the Boodie and Woylie diggings had the same sloped, conical shape as eastern bettongs but are much larger, around 15cm in diameter and 10-15cm deep, while eastern bettongs only dig down around 5cm. This might indicate that the truffles are buried deeper in the drier soils, and would have implications for the amount of effort taken to get the same amount of food, and the amount and depth of soil disturbance.
Noel said that the digs are great spots for seeds to collect and germinate, and described them as ‘perfect flowerpots’ – although I saw very little evidence of this at this time of year, only a few dried up ward’s weeds (Carrichtera annua) growing in the digs. Another interesting aspect is the impact of the digging on the biological soil crust, which was a diverse mix of lichens, mosses and liverworts. These cryptogams help to increase water infiltration and prevent erosion and run-off, but I wonder how the disturbance affects these qualities and how long it takes for the dig to fill in and the crust to reform.
After dinner, as the sun went down and the temperature started to drop, we ventured back out into the mallee to look for the diggers themselves. We had to walk carefully to avoid stepping in all the holes! But we did manage to see a few Boodies, a Brush-tailed Possum, heaps of bats and a fast-moving flash that I’m assured was the back end of a Bilby. Later that night we also had the opportunity to drive to a wombat warren in another part of the reserve, where we were lucky enough to catch a glimpse of a couple of Southern Hairy-nosed Wombats.
After only a few hours’ sleep, we were up again before the sunrise for a bit of bird watching. We didn’t have to go far; the area around the education centre was absolutely teeming with birds, attracted to a small water trough nearby. We saw Mulga Parrots and Purple-crowned Lorikeets and lots of others, although I was too busy looking at the ground hoping to catch a glimpse of a Numbat just waking up (no such luck). Numbats are one of the few animals that are day active, because they eat termites that only come up to the surface at warmer temperatures. It’s easy to see why the animals are mostly nocturnal though – by 7am it was already pretty warm and heading for another 40 degree day.
The last stop on our trip was to a wombat warren outside the feral-proof fence. Southern Hairy-nosed Wombats are quite social and dig huge complex warrens that can go many metres underground. Many other animals (such as bettongs, wallabies, reptiles etc.) use the warrens to escape the heat and predators. The wombats also have a big effect on the vegetation surrounding the warren, and Gunnar Keppel and his students* from the University of South Australia have been studying the vegetation and the wombats’ diet.
Previously it was thought that the wombats ate mainly native grasses, but in the Murraylands native grasses are not available for much of the year. Using DNA extracted from wombat scats, we now know that they eat a range of native grasses, shrubs and forbs, and also some weeds – in particular the Thread Iris (Gynandriris setifolia) which is a small geophyte with a nutritious tuber. Up to 70% of the wombats’ diet is made up of these tubers at certain times of the year, so it seems that they provide an important resource (Allen 2013). But this also means that the wombats are disturbing large areas to dig up the tubers, and this may be changing the vegetation and encouraging other weeds to invade – including potato weed which is thought to be toxic to many animals including the wombats.
The field trip was a fantastic experience; it was particularly interesting for me to see the complex relationships between the local and reintroduced digging animals and the vegetation in an arid system, and I learned a lot that will inform my research. I feel very lucky to have had the opportunity to visit Yookamurra and see the great work being done there by AWC and the researchers from the University of South Australia.
*Joshua Allen (2013) Inter-seasonal variation in the diet of the southern hairy-nosed wombat (Lasiorhinus latifrons). Honours Thesis, School of Natural and Built Environments, University of South Australia, Mawson Lakes, South Australia.