Body language in equids, with particular reference to the 'chestnut', part 1
(writing in progress)
I have spent much time studying the details of colouration in equids (e.g. ear markings) and a particular detail of anatomy (the size, tone, and location of the chestnut on the foreleg).
Do these subtleties matter in the intraspecific communication system of equids?
Many biologists might ask ‘what do such details matter in the scheme of things, particularly given that many equids have such gross patterns of colouration such as full-body striping, which surely outweighs such fine details?’ Another possible query might be: ‘We haven’t even worked out how the gross striping and other major patterns of colouration in equids functions, so why preoccupy oneself with all this fine detail?’
What many naturalists may not realise is just how sensitive the eyesight of equids is to tiny details of form and movement.
Equids have large eyes, even by the standards of other ungulates. Furthermore, it has been shown beyond doubt that the domestic horse is capable of reading human body language so subtle that even humans can hardly pick up on it.
The classic case is Clever Hans, please see https://en.wikipedia.org/wiki/Clever_Hans .
Clever Hans, a horse that lived at the turn of the last century, was so good at picking up tiny shifts in posture in humans that it could virtually read their minds, in the sense of using these visual cues to give humans the answers they wanted to various quantitative questions. The horse tapped out numbers with its foot, which is impressive enough. However, it got the correct answers because it could see humans who know the correct answers, and even though these humans were making no attempt to give the horse clues the horse was still reading these clues in the form of extremely subtle body language.
Now, it is one thing for a prey species of open terrain, such as the horse, to have excellent vision, particularly for even the slightest movements. That is fully understandable. However, what Clever Hans showed is that the visual and mental system of the domestic horse – despite any dumbing-down by artificial selection for docility and obedience – went far beyond the mere perception of danger. The horse is capable of using body movements as language, in the sense that it ‘read’ with a subtlety far beyond what could ever possibly be needed in anti-predator behaviour.
If such powers of perception are far ‘over the top’ for detecting danger directly, the most plausible explanation is that they function socially, including the enhancement of gregariousness in detecting prey. In other words, not only are equids reading each other physically in extremely subtle ways as part of their social interactions, but they are possibly monitoring each other so that any detection of danger by one individual is instantly communicated to all members of the herd.
They are, in a sense, using a kind of ‘internet’ intraspecifically. I’m not claiming that equids are capable of mind-reading, although it’s possible that they are indeed capable of that. What I’m claiming is that the visual communication system of equids is so astonishingly subtle and fine-tuned that what might look to us like trivial changes in appearance come over loud and clear to the equids.
If so, one can see how apparently trivial details of anatomy and colouration, such as the back-of-ear patterns and chestnut, could function to announce messages at the same time as being nested within an overall pattern that functions to hide the animal from predators or confuse the predator’s target-image during attack. In other words, equids could be a combination of gross-scale and fine-scale patterns which operate at different levels.
If one accepts this conceptual framework, something as subtle as the form and appearance of the chestnut can suddenly become relevant.
The chestnut is a fine detail of equid anatomy - so fine indeed that the literature largely disregards it. However, the variation among lineages of equids is surprising.
When I first started to look at the chestnut, I made the same assumption that I think most zoologist would have made: that the chestnut is some kind of evolutionary vestige (a bit like the dewclaw in dogs) and that owing to this ‘ancestral’ reflection it would turn out to be similar in all equids.
The tacit idea here is that certain small features of anatomy do not matter but simply persist in forms that don’t get in the way, e.g. nipples in male mammals. So I was not expecting to find clear differences in form or appearance of the chestnut when I first started to flick through photographs a week ago.
What I found, instead, is surprising variation among lineages of equids, w.r.t. the chestnut, i.e. the kind of pattern one would expect for an anatomical feature that is very much functional and still subject to natural selection.
For example:
African wild asses differ from Asiatic wild asses, the chestnut being small in the former but large in the latter.
The domestic donkey seems to have ‘evolved’ a larger chestnut than its recent ancestor the African wild ass.
The chestnut in horses is surprisingly different in location and form from those of asses and zebras.
The various zebras vary greatly in the appearance of the chestnut, in a way that correlates only partly with patterns of striping on the foreleg.
Within a single species, Equus quagga, we have a wide range of conspicuousness of the chestnut, from virtually hidden by striping in the Mozambique zebra to a virtual punctuation mark in the extinct quagga. Although ALL the striping has been ‘blanked out’ on the legs of the extinct quagga, its chestnut remains prominent and so the chestnut is the main feature of colouration on the legs in this subspecies. It is, indeed, so conspicuous in the extinct quagga that it is extremely unlikely – given the extreme finesse of equid vision described above – that it would not have been used in the intraspecific communication system of the quagga.
In other words, this is what I am starting to think: that in certain equids such as the extinct quagga, the chestnut was analogous with PUNCTUATION in human written language.
At this point I find myself having reached the limits, both conceptually and terminologically, of the existing ‘paradigm’ in biology, and so it gets hard to communicate my hypotheses. What we face is the challenge of pioneering a new way of thinking about visual communication in animals.
Here is a crude start:
The chestnut of the extinct quagga (and indeed all Asiatic wild asses) is a PUNCTUATION MARK, valuable for interspecific communication via movement of the body. The idea here is that equids ‘read’ each other’s movements in a way analogous with how we read words on a page.
If I am right, we have the prospect of a new insight into the colouration biology of the quagga, because at face value this animal comes over as having lost much of the detail of zebras in its appearance. I.e. the quagga comes over as ‘blurred’ and even ‘degraded’ owing to the ‘dissolution’ of fine detail in its striping – including, by the way, the pattern on the back-of-ear. The chestnut hints that there’s more to this than meets the eye?
All perissodactyls, including equids, may be more vulnerable to predation than coexisting ruminants. This is because the intensity of predation is basically set by the reproductive rates of the ruminants, but the perissodactyls all reproduce slowly relative to ruminants.
So, to take an example: if 1000 gnus support 10 lions, and 100 zebras live in the same area, the lions will tend to take the zebras at the same rate as the gnus, but the zebras cannot replace themselves as rapidly as the gnus. The relatively slow rate of replacement of predated individuals in equids is because of slower somatic growth and delayed sexual maturity.
Equids gestate for about a year whereas like-size ruminants gestate for only about 8 months. Zebras do have a growth-spurt when juvenile, to outgrow the smaller predators as rapidly as possible, but then they reach sexual maturity a year or three later than like-size ruminants do. (Zebras also live longer than like-size ruminants do, which of course makes sense). This combined with the fact that zebras are fattier (yellow subcutaneous fat, inter alia) than any wild ruminant other than elands exacerbates the situation. So as I see it zebras need to be better-defended against predation than like-size ruminants, which helps to explain their bizarre colouration of stripes. Part of the whole picture is that equids have proportionately larger eyes than ruminants despite being diurnal (i.e. the huge eyes of zebras are not explained by nocturnal vision).
So, to my mind it makes sense that the visual faculties of zebras should be superior even to those of ruminants (which have excellent vision in the scheme of things), and that there should be additional features facilitating the monitoring of conspecifics, e.g. the chestnut.
I do not think that horses (domestic or wild) use the chestnut for communication, because these equids have an inconspicuous chestnut. However, I do think that Asiatic wild asses and some subspecies of plains zebra use the chestnut for communication.
I suspect that equids are extremely efficient at reading the punctuation of the chestnut, rather than having a particularly complex syntax in which this punctuation occurs. I.e. I think the emphasis is on getting a great deal of information from an extremely rapid glance or scan, while the head is down, grazing.
We humans read slowly but with great depth/complexity. Equids read rapidy but with superficiality, because most of what they are doing (in the case of the chestnut at least) is simply to monitor the ‘mood’ of conspecifics in a scattered herd. In a relaxed mood while routinely grazing, the chestnut (which can be seen even from a head-down position because of the location of the chestnut on the leg) moves intermittently in a certain pattern as the grazing conspecific gradually progresses across the lawn.
This pattern of movement is what I think the watching equid is monitoring, and it’s doing this for not one but perhaps up to 20 conspecific individuals in a single sweep of the eye, while not even stopping its noisy chewing at ground level.
The literature on the domestic horse seems quite clear (without disagreement) that individuals of Equus caballus show a great deal of body and facial language, some gross, some subtle. Any of dozens of books on the horse will explain in some detail the movements, gestures, and expressions involved, all of which seem to have been fairly thoroughly studied. It comes down to posture and facial expression mainly (including even expressions of the eyes).
This is why someone like Monty Roberts has been able to achieve such astonishing subtlety in training untrained horses, simply by ‘body-talking’ to them in a way that most human observers would miss completely. He’s written a book about this, earning him the title of ‘horse-whisperer.’ I think that similar principles were used by various populations of native Americans who used horses intimately in lands ranging from the American prairies to the Pampas. No kit or gear or even reins, just efficient communication between human and horse by means of subtle signs and gestures.
But, again, equids are not particularly cerebral in the way that some primates are, the impressive thing is the efficiency more than the complexity. In their own way equids have faces as expressive as those of humans, although most human spectators miss these expressions because they’re not educated to notice them and they partly use different facial structures such as the ear pinna. The horse even fang-bares like a carnivore.
Humans are more complex in body language (e.g. hand-gestures) than an equid can be, but the horse is probably more efficient than a man at reading appropriate gestures, i.e. it can do so extremely rapidly and based on extremely small movements, i.e. the letters and words in the ‘virtual script’ are seen in a kind of exaggerated differentiation.
Imagine how an illiterate would regard the printed page as a meaningless jumble, or how we Europeans see both Chinese faces and Chinese literary characters as ‘all the same’. A horse might have only a few hundred words in its vocabulary but it reads them as writ large even though they’re writ small, and does so with extreme economy of eye and head movements, using a panoramic retina that makes no particular attempt to focus but, as it were, reads 20 pages all at once. In a typical panoramic view there might be up to 20 conspecific individuals scattered about at various distances from the viewer.
The viewer can take in that entire seen in one glance lasting only a fraction of a second, using the accentuation provided by features including the chestnut (in the case of non-territorial spp. of equids such as E. quagga and E. khur, but not territorial spp. such as E. grevyi and E. africanus which live in relatively small groups and know every individual around them most of the time), in the same sense that punctuation in our own writing serves to accentuate the dynamic features of the writing.
Punctuation in our writing helps to give ‘flow’, and I suggest that punctuation in the extinct quagga and Asiatic wild asses similarly aids in conveying ‘flow’ to the eye of the beholding equid.
(writing in progress)
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