More on the back-of-foreleg bar in the common eland, including a new partial explanation

 (writing in progress) 

The common eland has a northern subspecies (Taurotragus oryx livingstonii, https://www.destinationuganda.com/travel-guide/mammals/common-eland/ and https://www.dreamstime.com/group-eland-scientific-name-taurotragus-oryx-pofu-swaheli-serengeti-national-park-tanzania-group-eland-image106269671).

This subspecies is peculiar in that, of all its markings, the most conspicuous is a back-of-foreleg bar, which can alternatively be called an ulnal flag.

The following illustrate the back-of-foreleg bar = ulnal flag in Taurotragus oryx livingstonii.

ADULT FEMALES
The following is a near-perfect depiction for the purposes of a field-guide: https://naturfotografen-forum.de/data/o/111/557352/image.jpg
Taurotragus oryx livingstonii adult female:https://upload.wikimedia.org/wikipedia/commons/0/0f/Elenantilope_Taurotragus_oryx_Tiergarten-Nuernberg-1.jpg
Taurotragus oryx livingstonii adult female: http://www.hlasek.com/foto/taurotragus_oryx_bf4175.jpg
Taurotragus oryx livingstonii adult female: http://wildlife-media.at/bild/43122/elenantilope-mit-madenhacker0Dmasai-mara-kenia.jpg
Taurotragus oryx livingstonii adult female: http://www.rauschenbach.de/Mali/mihingo%20waterhole%20Bild%201628.jpg
Taurotragus oryx livingstonii adult females: https://c2.staticflickr.com/8/7060/13452917915_9aaf6afe4c_b.jpg
Taurotragus oryx adult female: http://2.bp.blogspot.com/-PTRKbQGbhO0/VL4rsuvDxVI/AAAAAAAAJTc/2i6jrLlpLNA/s1600/Elenantilope%2B2014_09_16%2BUG%2BMburo%2BFZ1000%2B167.jpg
Taurotragus oryx livingstonii adult female: http://l7.alamy.com/zooms/70ccf7fe19cf4adb90e1fb626efb0504/elenantilope-taurotragus-oryx-nrnberg-bayern-deutschland-e0fafj.jpg
Taurotragus oryx livingstonii adult female: http://images.fotocommunity.de/bilder/saeugetiere/pflanzenfresser-schweine/eland-antilope-29c92664-3a73-4356-b86e-6847bcf429ba.jpg
https://www.dreamstime.com/antilope-africa-savanna-wildlife-safari-antilope-antelope-africa-savannah-wild-nature-african-wildlife-game-safari-image205158958
https://www.dreamstime.com/common-eland-taurotragus-oryx-southern-antelope-savannah-plains-east-africa-species-family-bovidae-genus-wild-image114964585
https://depositphotos.com/543911962/stock-photo-common-eland-taurotragus-oryx-large.html
https://www.dreamstime.com/common-eland-taurotragus-oryx-southern-eland-eland-antelope-savannah-plains-antelope-east-southern-africa-image115575217 and https://www.dreamstime.com/antilope-antelope-africa-savannah-wild-nature-african-wildlife-game-safari-natural-reserve-savanna-image206639043 and https://www.dreamstime.com/antilope-antelope-africa-savannah-wild-nature-african-wildlife-game-safari-natural-reserve-antilope-africa-savanna-image205158959
https://www.dreamstime.com/common-eland-taurotragus-oryx-southern-eland-eland-antelope-savannah-plains-antelope-east-southern-africa-image115575182

ADOLESCENT MALES
https://www.dreamstime.com/eland-standing-long-grass-looks-back-image132824701
https://www.dreamstime.com/royalty-free-stock-images-beautiful-giant-eland-antelope-largest-entelope-world-image37754459
https://www.dreamstime.com/stock-image-beautiful-giant-eland-antelope-savanna-grassland-largest-entelope-world-image37943041
https://www.dreamstime.com/common-eland-stands-grass-profile-image163837293
https://www.dreamstime.com/stock-photo-common-eland-tragelaphus-oryx-male-image77404827

ADULT MALES
https://www.dreamstime.com/royalty-free-stock-image-eland-largest-antelope-africa-image15636256
https://www.dreamstime.com/common-eland-bull-red-billed-oxpecker-mana-pools-national-park-zimbabwe-image172742545
https://prehistoric-earth-a-natural-history.fandom.com/wiki/Common_Eland?file=1a7fc4b7089a77ee51b3f5d2c51fe3a9.jpg

MATURE MALES
Taurotragus oryx livingstonii mature male: https://upload.wikimedia.org/wikipedia/commons/7/70/Taurotragus_oryx_-Disney's_Animal_Kingdom_Lodge,_Orlando,_Florida,_USA-2010-01-19-_03.jpg
Taurotragus oryx livingstonii mature male: http://safaritalk.net/uploads/gallery/album_1134/gallery_19319_1134_17249005.jpg
Taurotragus oryx oryx mature male:http://www.lexikon-tiere.de/elenantilope.jpg

JUVENILES AND ADOLESCENT FEMALES
https://www.dreamstime.com/stock-image-two-eland-masai-mara-image10679161

ADOLESCENT FEMALES
https://www.dreamstime.com/common-eland-taurotragus-oryx-single-mammal-kenya-september-image161969370
https://www.dreamstime.com/common-eland-taurotragus-oryx-grazing-trees-common-eland-taurotragus-oryx-grazing-trees-grassland-habitat-image174523119
https://www.dreamstime.com/common-eland-taurotragus-oryx-grazing-trees-grassland-habitat-common-eland-taurotragus-oryx-grazing-trees-image174523144
https://www.dreamstime.com/common-eland-taurotragus-oryx-grazing-trees-grassland-habitat-image174523066

The following shows the lower cheek-spot and nearly the maximum size of the dewlap-tuft. The mid-ventral stripe is surprisingly poorly developed. The neck is not as grey or as pale as in T. oryx oryx. There is no sheen on the cheeks in this illumination.
 
The following individual again shows the lower cheek-spot. The mane is well-developed, but the tail-tassel as small as is typical in T. oryx oryx. The dewlap is as large as it ever gets in the female, but in this individual lacks a dark dewlap-tuft. There is no blaze on the cheeks and junction with neck, possibly because of the angle of the light. The dark apical back-of-ear with its tiny white tip is just discernible.
 
The following is an unusual individual lacking vertical stripes, despite conforming in every other way with T. o. livingstonii.
 
The following shows all the ‘points’ that ‘punctuate’ the female northern eland. The colouration of the neck and cheeks is typical.
 
The following shows the general lack of sexual dimorphism in colouration.
 
Taurotragus oryx livingstonii subadult female (right), mature male (middle), adult male (left foreground):
http://l7.alamy.com/zooms/eae06b93fa644d3ab235d88085117219/eland-taurotragus-oryx-lake-mburo-national-park-uganda-eg9tey.jpg

The following shows that the neck does not give an overall pale impression in the female northern eland, and that the dewlap-tuft is not nearly as conspicuous as the tail-tassel.
 
The following shows the pale ‘blaze’ of the cheeks, which shows above the vegetation cover when the animal raises its head to browse. It also shows that the underside of the tail shaft near the tassel is whitish. Note the bleached dewlap-tuft.
 
The following shows the precociality of the mane on neck and withers, which actually seems to become proportionately shorter in adults. Juveniles are somewhat brighter-hued than adult females.
 
Taurotragus oryx livingstonii adult females & juveniles:
http://www.naturfoto-cz.de/bilder/auer/elenantilope-IMG_1384fmw.jpg

The following individual has a modest tail-tassel but well-developed mane and mid-dorsal stripe, and also a dark dewlap-tuft. The moderately dark face is typical. The limited extent of pale at junction of cheeks and neck is typical. Note the lack of any balding on shoulders or neck.
  
The following zoo specimen, shorter-legged than in the wild, shows all aspects of the typical colouration.
 
Taurotragus oryx livingstonii:
http://www.biolib.cz/IMG/GAL/BIG/26750.jpg

The following shows the infant, complete with both cheek-spots and only a tiny hint of the dewlap-tuft. The body proportions are extremely juvenile but the colouration essentially already adult.
 
Taurotragus oryx livingstonii:
http://www.zoo-wuppertal.net/0-pics/4-tiere/saeugetiere/paarhufer/horntraeger/elenantilope/2011/20110624-nachwuchs/20110624-049-elenantilope-jungtier+.jpg

The following shows the typical cinnamony cervical fur-patch and the tonal contrast on the ‘chin’. The mid-ventral dark stripe is poorly developed.

The following shows that, at this angle, the sheen on neck and cheeks is NOT apparent. The small size of tail-tassel is typical, one of the most reliable differences between the two subspecies. Note the limited extent and limited intensity of the hoof-linings.
 
Taurotragus oryx oryx mature male & mature female:
http://l7.alamy.com/zooms/7031c4364000411c962d901374ff8a97/eland-in-tala-game-reserve-near-pietermaritzburg-kwazulu-natal-south-c79dbt.jpg

The following is typical for the southern subspecies in colouration although, as a zoo specimen, rather mishapen.
 
Southern eland:
 
Neck pale and shiny; back-of-foreleg bar not noticeable; tail-tassel small and faded; mid-ventral stripe not noticeable.
 
Taurotragus oryx oryx mature male:
http://www.safarinjema.com/uploads/images/Eland.jpg

Northern eland:
 
Neck no paler than body; back-of-foreleg bar noticeable; tail-tassel large and dark (not well-shown by this photo); mid-ventral stripe noticeable.
 
Female:
 
Vertical striping present; neck no paler than body except near junction with cheek (not well-shown by this photo); back-of-foreleg bar noticeable; tail-tassel large and dark; hooves with noticeable dark borders (the latter point not well-shown by this photo). 

This bar is not,  in itself, unique. Most tragelaphins (https://en.wikipedia.org/wiki/Tragelaphini) possess dark pigmentation in this part of the anatomy, corresponding approximately to the ulna.

However, what is unique to the northern ssp. of the common eland is that this bar is retained in particularly vivid form, whereas the rest of the animal is relatively plain.
 
So, what is the adaptive function for the back-of-foreleg bar in a subspecies of this, the largest of all antelopes?
 
I suspect that the answer is infrasound.
 
Any sound of frequency <50 Hz is inaudible to human ears.

However, various large mammals use such sounds, and this extends down to ungulates as small as the okapi (Okapia, https://en.wikipedia.org/wiki/Okapi), which has about the same body mass as the common eland. This is known by virtue of fieldwork in zoos by Elizabeth von Muggenthaler. See, for example, https://www.semanticscholar.org/paper/Giraffe-Helmholtz-resonance-Muggenthaler/e307549059070fd66e6f3183282ce550240f41d3 and https://www.researchgate.net/publication/288641659_Giraffe_Helmholtz_resonance and https://asa.scitation.org/doi/10.1121/1.4800658.
 
Over the last few decades, there has been a growing list of large ungulates known to communicate in infrasound. It has, therefore, been a matter of time before the common eland is added to this list. This is an extremely large-bodied antelope. Furthermore, like the giraffe, it seems remarkably silent to human ears.

A clicking sound so known in mature males of the common eland, made by a guitar-like effect of the sinews in the carpal joint.

What has occurred to me is that this may have an infrasonic component. I suspect that it is not just mature males but all adults, and possibly even juveniles, of the common eland that communicate frequently via infrasonic clicking/twanging of the ‘wrists’.
 
The common eland is gregarious. However, it tends to forage in a rather scattered formation (much like giraffes), because of its partly browsing habits. It also tends to be extremely mobile, indeed fully migratory in many populations. And extremely flighty, fleeing from vehicles even when these are still far away in national parks.

So, for group-members to stay together can be challenging, particularly in patches of relatively dense vegetation or at night.

I hypothesise that the common eland uses the infrasound emanating from the clicking carpal joints to facilitate the monitoring of each other’s whereabouts by herd members.
 
A paper was recently published in which the clicking by mature males was studied. It was found that the click can be used as an audial expression of the body mass of the individual, thus facilitating inter-male rivalry. That may well be true, but what the authors did not seem to consider was that the same clicking sound a) has an infrasonic component that can be made even by small individuals of the species, and b) functions also in routine communication in aid of group-cohesion. This would explain why there is nothing special about the mature male in the possession of the back-of-foreleg bar; it is equally well-developed in females and indeed is present in full form already at birth in both sexes equally.
 
The point of the new idea is that the clicking of the carpal joint is the audial version of an optical signal: the flashing of the back-of-foreleg bar as the animal walks away from the observing individual. The animal gives off two sensory clues to the fact that it is walking, and the direction in which it is walking. If the observer cannot hear the striding, it will be able to see it; and if it hears the clicking (in infrasound in most cases) it will be able, by observing the timing/coordination, to pinpoint the location of the individual making the clicking.
 
I also suspect (as an implication of all previous observations in the literature) that, even in mature males, the carpal clicking can be ‘switched on and off’ voluntarily.

It makes sense that such a loud sound would not be compulsory in a species that has a secretive component to its behaviour, and which certainly has an element of concealment in its colouration (in the case of the northern eland, essentially the same disruptive pattern that confers camouflage in tragelaphins generally, albeit in rather rudimentary form). I also doubt that the clicking continues when the eland breaks into a trot (I don’t think that has been studied yet in the field).
 
So this is my new hypothetical perspective on the northern ssp. of the common eland: when you look at an adult female walking away from you (for this is the angle from which the back-of-foreleg bar is most noticeable), you are looking at an animal which is often (unless alarmed and trying to slip away silently) simultaneously clicking away infrasonically with its carpal ‘twang’.
 
In a nutshell, the new idea is that the distinctive back-of-foreleg bar of the common eland is the visual equivalent of an infrasonic click, used for emphasis (amplification as it were of the announcement that a herd member is departing) and for ‘triangulation’ to determine as rapidly as possible the precise location of this individual.
 
I predict that it is only a matter of time before some field scientist is able to show, using the right equipment, that

• the carpal clicking in females is voluntary (switched on and off),
• the carpal clicking in females is infrasonic (<50 Hz and therefore inaudible to humans and also many of the natural predators of the common eland), and
• that the sensory system of the common eland is easily able to detect both the sound and the visual ‘strobing’ produced by the stride (the eyes of ungulates being extremely sensitive to movement, even in dim light).

If I am right, the implication is that, although the back-of-foreleg bar may retain some function as a DISRUPTIVE marking (i.e. one helping to confer camouflage, e.g. in dim light or small groups in relatively dense cover, when the northern eland ‘freezes’ to allow a predator to pass it by without spotting it), the concealing function of the bar is trivial relative to its ADVERTISING function. I.e. interspecific concealment vs intraspecific advertisement, the latter winning hands-down as the main function of the back-of-foreleg bar.

Please remember that, to fulfil the camouflaging function, such a bar could have been located in various places on the legs or elsewhere on the animal’s physique. The fact that it located virtually at the carpal joint, where the distinctive clicking known to occur in the common eland emanates, seems to me to be too much of a coincidence.
 
(writing in progress)

Publicado el julio 9, 2022 10:17 TARDE por milewski