Gippsland Bobucks:
future research prospects.
The Bobuck Survey of 2006 - 2008 is finished and done, folks. No more field trips and no more robot photography in Gippsland for me. But, you never know, others may wish to look more closely at these curious critters at some time in the unknown future.
I sure hope so. Mainly because I have a hunch that a closer look just might pay a handsome scientific dividend. If I were a zoology student, or a zoology student's academic supervisor, and if I were casting about for a research project I'd be mighty tempted by these little guys.
Debbie Hynes
Southern Bobucks:
a case of Darwinian adaptation?
| January, 2010. |
Given that these animals occupy an environmental niche that is atypical for their species, one wonders if the population in SW Gippsland may represent a case of evolution at work?
Most readers would, of course, be familiar with Charles Darwin's theory of evolution by natural selection. The insights given us by Darwin constitute the most profound revolution in history in our thinking about how Nature works, about the origin of our own species and, indeed, of all living things upon the planet Earth.
The truths that Darwin uncovered are deeply unsettling and even today some religiously minded folk have trouble coming to terms with the full implications of his ideas.
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Foxes deterred?
Conventional wisdom holds that Bobucks require den hollows in trees to protect themselves from the freezing cold of winter nights in the mountains and for refuge against predators. Obviously, severely low temperatures are not a factor in lowland, coastal Gippsland.
Gippsland Bobucks do not appear to require tree hollows at all. Many, indeed most, of the areas where this survey detected them offer only young regrowth eucalyptus or spindly Tea Tree. Acacia species, in particular Acacia dealbata, are present in some locations but absent in others: there is no correlation of Acacia with the presence of Bobucks, however. Suitable tall-tree hollows appear to be in grievously short supply. Yet predation pressure on the species in the Victorian alps is said to be so severe that both Bobucks and Common Brushtail possums will only resort to ground denning if forced to (How, 1972; Cowan, 1989).
A curiosity of the survey was that foxes and Southern Bobucks apparently do not mix.
When examining images collected, it even came to be a rule of thumb: if the cameras observed foxes, there would be no Bobucks at that location. If Bobucks appeared in the first images, no foxes would be seen.
But we know that the Bobucks of Gippsland are to be found in areas (Gurdies/Bald Hills) where fox numbers are very high and where few suitable tree refuges are available. These Bobucks appear to spend nearly all their time on the ground, where foxes are. Yet they are thriving.
Have they perhaps evolved some means of deterring Reynard the Fox? Uniquely(?) among marsupials, males and females of this species form monogamous pair bonds and they defend a territory together. In such a case the entire group, parents and offspring, would be full siblings. Evolutionary theory tells us that such groups do indeed act with greater cohesion than unrelated individuals. Perhaps they have evolved a system of group defense against against predators, based upon altruistic behaviour engendered by kinship?
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All this is pure speculation but, if correct, it could be important. Conventional wisdom would have it that what the Bobucks in Gippsland are doing they ought not to be doing. Small and medium sized native animals are believed to be massacred by exotic predators like foxes, feral cats and dogs. Yet here is a smallish, ground dwelling native marsupial that is not only surviving but thriving in the face of such odds. They may even be able to drive foxes away: that is unheard of. It could even open up possibilities for the conservation of other, less reslient, Australian marsupials.
Bobuck "Corridors"?
An obvious question about these Bobucks is how did they come to colonise south west Gippsland? Are wildlife corridors important for their success? They do not appear to need the same food resources as their mountain cousins: Acacia dealbata does not seem to be a decisive factor for their range and the literature suggests that, unlike Common Brushtail Possums (Trichosurus vulpecula), they can't metabolise terpenes present in eucalyptus leaves. So what do they subsist upon?
Two elements of their environment that do appear to be important for them are water and ground cover. Wherever the Survey found Bobucks, a source of surface water was nearby. They don't seem to favour tree stands where ground cover such as bracken or reeds are absent, either.
Taken together, do these factors mean that they use water courses to penetrate inland? Our hunch is that they do. If so, then water courses may be important wildlife corridors not only for Bobucks but for other animals as well. Every effort should be made to conserve such habitat. Revegetation programmes, such as conducted by Landcare and the DSE should be continued. It's having an effect!
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Bobuck Tunnels???
This is actually where the informal name for my Survey comes from: the Bobuck Underground.
At two locations, namely The Gurdies Reserve and Koonwarra, the cameras detected bobucks apparently coming and going from underground tunnels. At first we assumed these tunnels were the result of wombats' work: yet of wombats there was no sign. Perhaps they were old, abandoned wombat tunnels, then?
At first, that is what we thought about Koonwarra. But then, at The Gurdies Reserve, we noticed a newly dug excavation, a large, unfinished tunnel dug into the root structure of a "Messmate" tree. We deployed a camera expecting to see an industrious wombat at work, at last.
But our camera saw not wombats but Bobucks! What? Everyone knows Bobucks can't dig tunnels. The idea seemed preposterous. And yet ... something digging the Gurdies tunnel had kicked fresh dirt onto the camera view-screen, as can be seen in the pictures below. No other animals but black Bobucks were seen and they were apparently entering the tunnel during its construction.
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All this is highly speculative, we'll readily admit. We have not proved that Bobucks dig tunnels because we haven't put a video camera down there to actually record what they're doing. The cameras we used only take still images.
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Our current suspicion - and that's all it is as of now, February 2010 - is that these Southern Bobucks' apparent association with underground tunnels may be due to the availability of desirable fungi. In other words, they're not excavating tunnels for habitation: rather, they're hollowing out underground cavities in pursuit of whatever fungus it is that they feed upon. The excavations could therefore represent the work of many Bobucks over a substantial time: the "tunnels" may encourage fungus growth and are not a habitation or refuge as such. In other words, perhaps they're "mining" for their food, returning to the dig site as the fungi re-grows?
Rather than an unprecedented innovation, this would rather be an extension of behaviour they're already known for in the highlands. There, they scratch about under the damp leaf litter of the forest floor for certain fungi. Perhaps the sorts of fungi that they seek only grow around the roots of trees in the dry sandy soil of Gippsland? Perhaps that is why the tunnels seem only to appear there? The root structure prevents the tunnel from collapsing in the loose, friable sandy-clay. Such soil is soft and easy to dig, which would greatly help animals who have no special physical adaptations for digging.
If the above speculations eventually turn put to be anywhere near the mark, then what we may have is a niche population of marsupials who have adapted to a severely disturbed environment by evolving novel behavioural strategies to feed themselves and to defend themselves. Actually, we would not say they have merely "adapted". We would instead say they have prevailed, against all odds.
So, what do the authors really think is going on with these Southern Bobucks in Gippsland? We don't know, of course, but it's just possible this might be a case of Darwinian micro-evolution at work, before our very eyes. In a mammalian species, too, which is not something you see every day. So yes, a zoology student or a research supervisor in search of something novel and perhaps important to study might do worse than take a closer look at the Southern Bobucks, Trichosurus cunninghami, of south west Gippsland.
Debbie Hynes
Mike Cleeland
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Copyright © 2009 to D. Hynes. All rights reserved.
