Bobucks & Brushtails: comparisons
One objective of this exercise was to answer a technical question: can automatic cameras distinguish between closely related and physically similar animal species? In order to make a (+) identification, it is necessary to be able to examine a specimen's "diagnostic" features in some detail. Can a robotic camera do this under "field conditions" - namely at night, in rain and/or temperatures below the dew point?
Bobucks, Trichosurus cunninghami, are similar in many ways to their cousins the Common Brushtail Possums, Trichosurus vulpecula. However, there are enough physical differences between the two that they are classified as separate species. Have the authors brought digital automatic photography to the point where small divergences can be discerned without the necessity for trapping the animals? In other words, can the cameras used in this exercise allow an observer to tell apart these two cousins?
In order to capture images with the necessary level of detail the camera must, obviously, be placed in close proximity to the subject. Since most Australian native animals are nocturnal in habit, operation at night is called for. These conditions are easy to specify but, until now, have been extremely difficult to implement "out there". So much so that professional wildlife photographers, using traditional methods of wildlife photography, have sometimes dismissed automatic photo traps as "a waste of time", Raithby & Beste (1971).
How can we be sure we have images of Bobucks?
Novel camera technology, developed by the authors, allows images of wild animals to be captured at close quarters in wilderness settings. But is it helpful for the purpose of identifying native fauna?
For visual identification, the ears appear to be the most prominent distinguishing feature between T. cunninghami and T. vulpecula. The ears of T. vulpecula are longer, relatively more slender and pointed than those of T. cunninghami. T. vulpecula has a lighter coloured coat and has a brown stripe running vertically down its chest. This feature appears to be absent on T. cunninghami.
In the table below we align head & shoulders excerpts from the images of the provisionally identified Bobucks with images of Common Brushtail Possums. The cameras used in this exercise can capture very many images: several hundred archived pictures of Common Brushtails are available to choose from. Therefore, we select frames where a Brushtail Possum's posture, body size and distance from the camera match reasonably closely those of the proposed Bobuck images. Are they the same kind of animal or do the images from Westernport show a different species?
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TABLE #1: Comparison of T. vulpecula with the Gurdies Animals.
The Common Brushtail Possum - Trichosurus vulpecula. The Gurdies Animals - are they Bobucks (Mountain Possums), Trichosurus cunninghami?
Profile view of an adult Common Brushtail possum. |
Note the raindrops on the animal's coat. Wet, rainy conditions clearly do not deter them from moving about at night. |
T. vulpecula foraging. |
The Gurdies Bobuck in similar mode. |
Crouching and watching the camera. Note the ears |
The Gurdies animal likewise attentive to the camera. |
Frontal view, ears alert. T. vulpecula. |
Frontal view, ears alert. A Gurdies animal looks heavier of build, broader in the face and with short, round ears. |
In left profile, T. vulpecula |
And a Gurdies Bobuck in left profile. |
Standing up, ears alert for danger. |
By contrast, the Gurdies animals' ears look more widely spaced? |
Mother and joey T. vulpecula surprised by a camera. Ears slender and pointed. |
A Gurdies T. cunninghami surprised by a camera. Much shorter, rounded ears clearly evidenced. |
Other Animals Photographed.
A question of interest is - what animals do these Gurdies Bobucks share their habitat with? The cameras detected Bush Rats, Rattus fuscipes, for one. Doubtless there are other fauna about - foxes and feral cats certainly, probably swamp wallabies and other marsupials. A longer survey would give a more complete picture of the Bobucks' environment.
The authors believe the animals here documented in The Gurdies may represent a relict that has been cut off from other population centres. How long they have been isolated is not clear at this time. Their absence from previous surveys, together with the sparseness of local lore about them or of sightings or captures in the district, suggests that The Gurdies population is extremely small. (@ 2006: later camera surveys showed the population is large and widespread.)
The authors feel that this circumstance is quite remarkable. These animals apparently live only a few hundred metres from the main arterial highway into South West Gippsland and Philip Island, namely the Bass Highway, yet they have remained uncatalogued and virtually unobserved for who knows how long.
Bobucks are basically an alpine species. The photos show they have many physical adaptations that allow them to cope with the extreme cold they must endure above the snow line in the Victorian Alps over winter : short ears, large body size, dark colour, generally "stumpy" build. These are attributes commonly found in cold adapted species because they help minimise the loss of body heat.
Yet it is apparent these Gurdies Bobucks have learned to cope with an atypical, tree lined swampy habitat near the shore of Westernport Bay. Presumably they are confined to scattered "habitat islands" such as this creek. Where other such "islands" are to be found is not known at this time. (2006: later survey work disclosed that they are very widespread.)
They would seem to represent an unusual adaptation by a peripheral subset of an established, alpine based species to a niche environment. However, the true explanation for their presence here in The Gurdies, is obscure at present. Indeed virtually everything about them - their origins, their numbers and distribution, their mode of living - is obscure at the present time. (As of 2006)
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Copyright © 2009 to D. Hynes. All rights reserved.
