North American moose turns to face human aggressors and make them regret their pursuit. Photo by Janis Powell.

I’ve said it before and I’ll say it again: one of the most familiar and frequently encountered of mammal groups (at least, to those of us in Eurasia and parts of the Americas) – DEER – are weird and fascinating when you get to know them. The whole antler thing is bizarre, but the behavioural diversity and flexibility present in this group is also remarkable and a nice illustration of how ‘familiar’ groups do so much more than people usually imagine. I’ve written about deer quite a few times on Tet Zoo before (see links below); here, I want to talk about a few unusual things they do that I haven’t discussed before. For knowledgeable readers: apologies if this is not new to you.

The Moose Alces alces is an incredible beast, for a whole load of reasons. Right now I want to concentrate on a few behavioural things about it. When confronted by predators, the majority of deer run away. And this is true for many moose – their large size, long limbs and endurance mean that they’re able to out-pace many potential predators.

Moose in confrontational pose used to face down potential aggressor. Herbivores and carnivores are not necessarily as different as we usually imagine. Illustration from Valerius Geist's 1999 Deer of the World.

However, moose also exhibit an interesting tendency to response aggressively to predators, sometimes facing them down, posturing at them and even roaring at them. In other words, moose will aggressively face-down predators and other aggressors. Geist (1999) described the aggressive moose roar as “more reminiscent of a large carnivore’s roar than that of an herbivore” (p. 237), and suggested that it might intimidate wolves. The head-down posture, down-sloping neck and raised hackles of a moose aggressively approaching a potential predator are all highly reminiscent of the aggressive posture practised by carnivorans. Is this a coincidence? This behaviour isn’t completely unique to moose within deer, since Sambar Rusa/Cervus unicolor will also do the same thing. Intriguingly, both Sambar and Moose are (often) especially dark compared to most other deer. The suggestion has been made that big mammals that respond aggressively to potential predators are often dark (Geist 1999). [Photo below by Yathin S. Krishnappa.]

A Sambar adopts a confrontational pose when confronted by Dhole (Cuon alpinus). Photo by Yathin S. Krishnappa, image CC BY-SA 3.0.

Some of you will have seen the recently released video of April 2014 where a husband and wife team pursue a moose on snowmobile but then regret their actions when the moose stops running, turns to face them, and approaches them in the aggressive, confrontational fashion just described. Afraid, they draw a handgun and fire a shot into the air to scare the animal away. I will refrain from being too judgemental. Whatever, they don’t shoot the moose and it escapes unjust and untimely death.

"Sambars are highly capable of moving about on their hind legs". More stuff from Geist's 1999 Deer of the World.

Moving on... some deer are surprisingly proficient at bipedal standing and walking. I’m not referring to behaviour whereby they stand momentarily while fighting, or lean their forelimbs on tree-trunks while standing up tall to browse at height; rather, I mean that they can actually balance and walk bipedally, unassisted, with the body held in a vertical pose. This behaviour is best known for Sambar, the males of which will stand and walk bipedally in order to mark overhead branches with scent or ‘horn’ them with their antlers. Note that intermittent bipedal behaviour is present elsewhere in deer – a few species stand bipedally to ‘box’ intraspecifically, or to fight off predators (including humans: link to mandatory video).

Pelvic and lumbar musculature of the fabled bipedal goat (below) compared with a normal, quadrupedal goat (above). Image from Slijper (1942).

Raising the body vertically requires the presence of modified muscles associated with the pelvis and lumbar region. Do sambar and other semi-bipedal deer have any particular modifications that reflect their bipedal abilities? I don’t know, and (so far as I can tell) no-one has done any work that seeks to test this. Some of you will be aware of the aberrant bipedal goat of 1939, born without forelimbs and which met a young and untimely accidental death at just a year old. It was described by Slijper (1942) and shown to possess a number of unusual pelvic and lumbar features not seen in normal goats. Relative to quadrupedal goats, it had more flexed hindlimbs and a narrower pelvis, longer gluteal muscles reinforced by novel tendons, diminutive psoas muscles, and a shallower, more barrel-shaped thorax (Slijper 1942).

Front cover of Geist (1999), a book cited several times in this article. Other books on deer are available, and Geist (1999) is certainly not perfect. However, it contains an extraordinary number of interesting observations and hypotheses.

While this individual goat serves as an excellent example of how phenotypically adaptive animals can be in the face of aberration, its anatomical peculiarities also help show which features are advantageous for a bipedal artiodactyl and would (presumably) be selected for in a lineage that took to using bipedal behaviour on regular occasion. Some of these features, and others, have been identified in the assorted extinct artiodactyls, sloths, chalicotheres and other mammals known or suspected to be habitual bipeds (Coombs 1983, Hooker 2007). Are they also present – perhaps in incipient form – in Sambar? I don’t know and haven’t seen any studies that might shed any light on this question.

And... some ‘historical’ questions: if we can identify osteological characters that link to bipedality in deer, is this a ‘new thing’ unique to one or two lineages? Is it a widespread thing that we’ve overlooked? Is it, even, a primitive thing that’s been lost in some or many lineages? And were the fossil relatives of modern Sambar equally as bipedal, or even more so? After all, the modern Sambar is only one of numerous, diverse Pliocene and Pleistocene ‘rusine’ deer (Leslie 2011).

More on deer some other time. Still aiming to cover the megalocerines some time.

PS - this is Tet Zoo ver 3’s 299th article. The next article - the Big 300 - will be unusual....

For previous Tet Zoo articles on deer, see...

Refs - -

Coombs, M. C. 1983. Large mammalian clawed herbivores: a comparative study. Transactions of the American Philosophical Society 73 (7), 1-96.

Geist, V. 1999. Deer of the World. Swan Hill Press, Shrewsbury.

Hooker, J. J. 2007. Bipedal browsing adaptations of the unusual Late Eocene–earliest Oligocene tylopod Anoplotherium (Artiodactyla, Mammalia). Zoological Journal of the Linnean Society 151, 609-659.

Leslie, D. M. 2011. Rusa unicolor (Artiodactyla: Cervidae). Mammalian Species 43, 1-30.

Slijper E. J. 1942. Biologic-anatomical investigations on the bipedal gait and upright posture in mammals, with special reference to a little goat, born without forelegs. Proceedings of the Koninklijke Nederlandse Akademie Van Wetenschappen 45, 288-295, 407-415.