Sarcophilus vs gulo part 4

(writing in progress)

Here’s an aspect that seems to have been quite overlooked by all previous writers on the topic of the Tasmanian devil: the relationship between scavengers and large, bone-gnawing rodents.
 
My main point is that it is impossible to understand the role of Sarcophilus as a bone-eater without the context that Australia is unique among large land-masses in lacking any large, fully terrestrial rodent that competes for the consumption of bones. Put another way: Australia lacks not only hyena-like eutherians but also bone-gnawing rodents of any considerable size or abundance, and this is why Sarcophilus, although of modest size and with only modest ability to break bones in its jaws, was the ‘top scavenger’ on the vast landmass comprising Australia, New Guinea and Tasmania.
 
In our comparisons with Gulo, it is easy to invoke the wolf and two species of bears as competitors with the wolverine for carcases and bones. However, it takes some lateral thinking to notice another competitor in the same environment: the North American porcupine Erethizon dorsatum.
 
Consider for a moment that this porcupine, although so easily overlooked in the boreal guild of bone-eating scavengers, is itself far more massive than Sarcophilus. The mean body mass for E. dorsatum is about 9 kg, compared with only about 6.5 kg for Sarcophilus. And, incidentally, it is far longer-lived as well, with a maximum lifespan of up to 30 years instead of 7.5 years.
 
Unlike bears, E. dorsatum does not hibernate, and so it potentially continues to consume bones through winter.
 
Now, one of the remarkable features of Australia – and one which is anomalous relative to the general theme that islands favour large rodents in place of other lineages of mammals – is that there are no large rodents indigenous to this continent. The largest non-aquatic species is Mesembriomys gouldii (about 0.6-0.65 kg) but this is restricted to tropical woodlands no farther south than the Gulf of Carpentaria. Hydromys chrysogaster can exceed a body mass of 1 kg and lives to this day in Tasmania, but is tied to water. The largest rodent in southern Australia is Leporillus conditor (about 0.35 kg), which reached no farther southeast than the northwestern tip of Victoria and was absent from Tasmania. The largest terrestrial rodent indigenous to Tasmania are Mastacomys fuscus and Rattus lutreolus (both about 120 g) and even these are restricted to the sort of dense vegetation which Sarcophilus – with its dependence on paths – tends to avoid. An indigenous rodent of about 0.2 kg, namely Conilurus albipes, occurred on the southeastern Australian mainland, but it did not occur in Tasmania and is now extinct.
 
Recent studies have shown how squirrels consume bones: https://www.bu.edu/research/articles/squirrel-bone-gnawing/ .
 
The following article shows that Erethizon dorsatum is frequently attacked by the wolverine: http://journals.sfu.ca/cfn/index.php/cfn/article/view/1727 .
 
So one cannot really understand the biology of Gulo fully without mentioning the largest rodents in its habitat, on which it preys and which compete with it for bones. What this means is that the main competitors for bones with Gulo are the wolf, two species of bears (warm season only) and the North American porcupine (possibly more in winter than in summer).
 
We can thus characterise Australia, in terms of bone-eating scavengers, in at least two different ways. Firstly, it is the only landmass – other than perhaps Madagascar where I suspect that extinct hippos filled this niche – on which the largest bone-eating scavenger weighed only <10 kg. Secondly, it is the only landmass on which the largest fully terrestrial, incidentally bone-eating rodent weighed <1 kg, with most of the landmass (i.e. the whole extratropical zone) having no such rodent >0.5 kg, and with the largest living rodent in the remaining habitat of Sarcophilus being only <150 g.

(writing in progress)

Posted by milewski milewski, June 07, 2022 17:59

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This documentary 'Wolverine, ghost of the northern forest' (https://docuwiki.net/index.php?title=Wolverine:_Ghost_of_the_Northern_Forest and https://www.youtube.com/watch?v=uUCwdHBoIfk) is worth watching with the audio on, because it is nicely done, informative, recent, and authentic.
  
A highlight of this documentary is that it shows an unexpected degree of sociality in Gulo. As in Sarcophilus, ‘solitary’ does not well describe this predator and scavenger. It has the kind of unapparent sociality possible in an animal with such extreme powers of smell that it is unnecessary for individuals to be near each other for them to have an active and interactive family life or social network. There is even a suggestion of paternal care in Gulo.
 
There is what I take to be authentic evidence of a wolverine being killed by wolves even with many tall trees close by into which the wolverine might potentially have escaped by climbing. What is most interesting about this footage is that the wolves seem to have made no attempt to eat the wolverine after killing it.
  
I think I may have been succumbing to exaggeration in my recent estimates of body mass. Perhaps the thick fur is fooling me. But the individual illustrated below, which is the largest of those depicted in this documentary, is only 16 kg. It looks about as large as the hand-reared specimen in my recent emails, which I estimated at 20 kg or more. I think I erred, and that the hand-reared specimen in question must have been considerably less than 20 kg.

(Nick wrote: When animals kill other species that are close competitors and potential predators hey usually dont eat them because its mote about warfare than predation. Wolves rarely eat puma but go to some lengths to kill them. Same for lions and  and leopards and hyena also different species of  eagles and i have seen the same phenomena when a devil killed a spotted-tailed quoll. One could even say the same for humans (re wolves etc). I wonder Iif the wolverine killed by wolves was injured or just svtewed up tactically.)

Posted by milewski 4 months ago (Flag)

Worth watching re the wolverine is https://www.youtube.com/watch?v=tO3BOPgEGMU , partly because it actually shows this carnivore chasing a snowshoe hare. As with most such documentaries, the best way is to mute the soundtrack so that the footage can be studied free of the banal narrative. From about minute 25 onwards we see the newborns, which are said to weigh about 80 g and prove to be surprisingly pure white.

From this footage I learned three things in particular.
 
Firstly, it is now clear to me that the tail is used as a ‘flag’ more by Gulo than by Sarcophilus. Although the tail is no longer in the former than in the latter, its distal half tends to be erected in Gulo in a way I’ve never seen in Sarcophilus; and because there is pale-dark contrast on the tail itself by virtue of the pale of the rump extending on to the proximal part of the tail in Gulo, the tail has a similar overall appearance as we see in Crocuta when that form of hyena is excited. Indeed, I can’t offhand recall any evidence of the tail being used for communication in Sarcophilus, apart from the fact that in a few individuals of Sarcophilus the very tip of the tail may be white. As regards the tail, it is Gulo rather than Sarcophilus that is more similar to hyenas.
 
Secondly, the vocalisations and hisses produced by the wolverine in antagonistic situations are interestingly complex. Although Mellivora vocalises characteristically in similar situations (and this is where the name ‘ratel’ comes from), my impression is the Gulo is less stereotyped and more nuanced in its vocalisations than Mellivora. Is Sarcophilus on the simple side, or on the complex side, in its vocalisations when confronting adversaries, whether conspecific or allospecific?
 
Thirdly, the footage of a wolverine walking along a fallen log showed me that the walking gait of Gulo in such situations is technically a cross-walk. Although this is by no means a perfect cross-walk such as we see in baboons in similar situations, it is also not the amble that most terrestrial mammals use. The walking gait of Gulo, at least in situations where stability is questionable, is similar to that of forms such as the klipspringer: it moves one limb at a time but, because left hind is lifted before right fore is planted (and right hind is lifted before left fore is planted) the gait falls into the category of cross-walk rather than amble. My examination of footage of Thylacinus walking suggests that the walking gaits of Gulo and Thylacinus are similar, and overall I find no suggestion of any important difference in walking gaits between Gulo and dasyurids in general. All of these forms walk by lifting one foot after another and in all cases the walking gaits are somewhere between a perfect amble and a perfect cross-walk. Monkeys cross-walk almost perfectly and the carnivores in question certainly do not walk that way; the polar bear ambles and the carnivores in question do not have as close-to-perfect an amble as does the polar bear.
 
Also, I was puzzled by the footage showing Gulo sparing a marmot for no apparent reason. I can only presume that this was a captive (hand-reared) individual of Gulo set loose for filming, and that it was so satiated that it was not hungry. But that hardly explains why the marmot seemed only mildly afraid of the wolverine. Something funny going on there? if you look in the final credits you’ll see acknowledgement of ‘captive animals’ in the plural. I infer that much if not most of the footage of Gulo in this film was of captive animals let loose for filming in set-up situations. This probably applies also to the scene of wolf vs wolverine.
 
In the sequence where the biologist takes a captured male individual out of the log trap, I estimate that this individual Gulo had a body mass of about 15 kg. This is at least double the body mass of Sarcophilus, not so?

Posted by milewski 4 months ago (Flag)

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