Journal archives for May 2021

May 12, 2021

Bleeze, flag and semet: necessary new words for describing adaptive colouration in ungulates

All of Biology depends on precise use of words. And much of what makes the thousands of photos of ungulates and other mammals on iNaturalist interesting is the patterns of colouration.

However, words to describe adaptive colouration have been so imprecise and inconsistent that it has been hard to write coherently on this topic. Both the anatomical parts and the features of colouration have been misnamed, or named by misleading analogy.

Describing the carpal joint - which is actually homologous with the human wrist - as the 'knee' is a gross example of this. Confusion between the withers and the shoulders is a subtler but equally important case. However, in anatomy at least the correct word already exists in most instances.

When it comes to important aspects of colouration, we may not progress in our thinking until we fill in the gaps in our lexicon. Here, I introduce three new terms: the bleeze, the flag and the semet.

Various ungulates feature a conspicuous pale patch, informally called a 'blaze'. A typical example is the blesbok (Damaliscus pygargus phillipsi), named after the Afrikaans translation of blaze. The metaphor applies because flame can be eye-catchingly pale, lighting things up. However, should we not avoid ambiguity with combustion? I suggest the new term 'bleeze', applicable only to the biological topic of colouration. We would describe the face of the blesbok as featuring a bleeze, not a blaze. An additional advantage is that bleeze can be defined to include conspicuously dark features, such as that on the face of the eastern white-bearded wildebeest (Connochaetes albojubatus) - or the juvenile of the blesbok itself.

The bleeze is, by its nature, large and prominent enough to be conspicuous to scanning predators even when the animal stands still. However, many large mammals feature pale/dark patterns which are easily overlooked until moved or raised. For these dynamic forms of advertisement, I suggest the term 'flag' instead. The most obvious examples are the caudal flags of the many species of ungulates which raise dark/pale tails in alarm or flight. However, in principle the term can also apply to the ears (e.g. impala, Aepyceros melampus), the feet (e.g. bush duiker, Sylvicapra grimmia), or the buttocks (e.g. steenbok, Raphicerus campestris).

The third word, 'semet', is newly derived from the Greek word for sign (think of semaphore or aposematic). This refers to dark/pale features too small-scale to matter for detection by potential predators, but moved in certain ways for social communication within the species. For example, many species of ungulates have subtle markings around the mouth, or at the base of the ears, which help companions to monitor each other's cud-chewing or listening - facilitating the spread of any alarm within seconds. And then there are many social signals involving colouration, used in rivalry and courtship, which are candidates for also being called semets.

Posted on May 12, 2021 01:23 by milewski milewski | 0 comments | Leave a comment

Introducing and naming cud-chewing displays

Many ungulates deal with predation partly by being gregarious. Even 'solitary' species may rest in sight of a mate or parent when ruminating, i.e. chewing the cud. A 'strength in numbers' is that the group - whether it numbers two or twenty - functions as a unit in cooperative vigilance by virtue of its collective eyes, ears and noses. The moment one individual becomes suspicious and stops chewing to listen up, the apprehension needs to be communicated efficiently across the 'white noise' of the tooth-grinding of group-members.

The point of mutual monitoring of the routine chewing of companions would be to detect any interruption immediately, and to direct attention accordingly.

Ruminants have a problem which humans do not: they spend much of their lives, both night and day, noisily grinding the cud - while at the same time maintaining constant vigilance by hearing.

The visual system of ungulates is extremely sensitive to slight movements. However, it makes adaptive sense that various species would have evolved patterns of colouration around the mouth to accentuate, or 'amplify', the chewing motion, particularly when the light is dim. And that each species would produce its own 'signature' pattern.

Is it possible that, once the naturalist has a search-image along these lines, the diverse patterns of dark and pale on the lips, chin, cheeks and muzzle of various ruminants may start to look less like random scribblings of capricious Nature and more like functional adaptation?

Here is one example to start with, illustrating the common eland (Taurotragus oryx): https://depositphotos.com/58556159/stock-video-common-eland-head.html.

Note the puzzlingly intricate pattern on the face. The dark muzzle contrasts with the pale mouth, and the whitish of the chin is bordered on its posterior side. Why would such a pattern have arisen?

In my last Journal Post I proposed the new term 'semet' for patterns of this small scale, functioning at the close range of social communication but not mattering much to the large-scale conspicuousness or inconspicuousness of the figure to scanning predators. Because this particular category of semet concerns movements of the mouth, I propose calling it a 'buccal semet'. We can expect the buccal semet of the common eland to be a dark/pale pattern unique to this species.

Of course the idea is still just hypothetical that ruminants are adapted to spot interruptions in the rumination of companions. And any new technical term may sound awkward at first. But could this open a new line of investigation into the subtle messages hidden in our photos of ungulates?

Posted on May 12, 2021 11:57 by milewski milewski | 1 comment | Leave a comment

May 04, 2021

Why no gazelle at the southwestern tip of Africa?

Mediterranean-type climates, with dry summers and rainy winters, occur both in South Africa and along the Mediterranean coasts of North Africa and the Levant. And gazelles have been evolving and shifting their ranges across Africa and Asia for millions of years. However, a puzzling faunistic difference is that four species of gazelles (Gazella cuvieri, Gazella dorcas massaesyla, Gazella gazella gazella, and Eudorcas rufina) are indigenous to the northern area whereas no species of gazelle is indigenous to the southern area.

In South Africa there is one species of gazelle, namely the springbok (Antidorcas marsupialis). However, this has not naturally penetrated the mediterranean-type climate of Western Cape Province. Furthermore, even within its distribution in South Africa the springbok avoids stony slopes, in contrast to Cuvier's gazelle in the Atlas ranges of Morocco-Algeria and the mountain gazelle, which is named after its association with stony slopes in e.g. Israel.

Why are there these disparities? One partial explanation involves competing members of the ruminant fauna.

A crucial difference is that the grey rhebuck (Pelea capreolus), mountain reedbuck (Redunca fulvorufula), common eland (Taurotragus oryx), steenbok (Raphicerus campestris) and Cape grysbok (R. melanotis) of South Africa have no counterparts in North Africa or the Levant. These species were, until recently, common in the relevant environments near the southwestern tip of Africa. Among them, they arguably usurped the niche of gazelles.

The grey rhebuck and mountain reedbuck prefer stony slopes, and the distribution of the former included most of the South African area of mediterranean-type climate. Both are similar in body size and partly similar in diet to the springbok. The common eland is extremely large (adult female about 500 kg) and the two species of Raphicerus smaller than gazelles, but all have diets which overlap those of gazelles enough for them to be potential competitors.

To 'rewild' the climatically similar stony slopes near Casablanca in the north and Cape Agulhas in the south of the same continent, we would reintroduce to the northern area only Cuvier's gazelle, but to the southern area at least three species: grey rhebuck, common eland and steenbok/Cape grysbok. One would be naive to think that the same ecological function could be restored by simply 'reintroducing' the springbok in Agulhas National Park (see photo by cypseloides, here in iNaturalist), even though it is by far the most similar antelope to Cuvier's gazelle that is available in the southern African fauna.

Posted on May 04, 2021 04:45 by milewski milewski | 0 comments | Leave a comment

May 06, 2021

A realistic approach to subspecies-identification in the springbok

Naturalists interested in the subspecies of the springbok (Antidorcas marsupialis) should read https://www.zobodat.at/pdf/Zeitschrift-Saeugetierkunde_46_0189-0197.pdf. Although now forty years old, Groves (1981) is still the best reference on a topic which will probably never be resolved satisfactorily.

Zoologists failed to document the nominate subspecies. The Karoo springbok (Antidorcas marsupialis marsupialis) occurred in Namaqualand, the Karoo, Eastern Cape, Free State, Gauteng, and the southern part of Northwest Province, with possible extensions into Mpumalanga, Limpopo, and even Kwazulu-Natal Provinces. Despite the extreme abundance of this form, the museums of the world have virtually no study-skins and only a few skulls. The Karoo springbok was, like the quagga (Equus quagga quagga), taken for granted until it was too late; and far fewer specimens were collected scientifically than for the quagga.

We cannot know exactly what subspecies marsupialis looked like in its original, fully wild condition. It is technically extinct because artificial reintroductions failed to discriminate against subspecies hofmeyri of the Northern Cape, and then there has been nearly a century of advertent and inadvertent selective breeding by farmers, partly to promote mutant genotypes. Body size is too adaptable to mean much, and the facial colouration varies individually in all the subspecies.

South Africa has thus lost its national mammal as a subspecific genetic entity, and more unfortunately we can never define what that entity was in the first place. Our best guess, based on a south-north cline from the northeastern Karoo to Angola (Groves 1981), is that the springbok of the Klein Karoo and Eastern Cape had extremely short, smooth horns in the female, and was not as pale as conspecifics in the Kalahari.

Groves found only 33 study-skins of the whole species of the springbok to examine in the museums of the world, and ironically 39% of these came from Angola and Kaokoland, which remain so remote that iNaturalist still features few photos from these areas. More particularly, we have the odd situation that subspecies angolensis is the best-represented of all the subspecies in terms of study-skins (13 of the 33 specimens examined by Groves), but so poorly represented photographically that to this day no photo shows clearly the darkness of colouration which Groves found relative to subspecies hofmeyri south of the Kunene River, in Kaokoland (also surprisingly well-represented, by 7 study-skins).

The false notion that angolensis extends to northern Namibia, including Etosha, seems to have arisen in Cain et al. (2004) Mammalian Species no. 753 (available free on the Web). Although ostensibly an authoritative summary of the springbok, this misportrayed the subspecies in its distribution map.

My suggestion for iNaturalist: for photos from Angola, assume angolensis; for photos from the Namib, northern Namibia, Botswana and the Kgalagadi Transfrontier Park, assume hofmeyri; and for all other locations just identify to species-level because the subspecies-status has been irretrievably compromised.

Posted on May 06, 2021 20:16 by milewski milewski | 0 comments | Leave a comment

May 07, 2021

At last, clear photos of the Angolan springbok

Rogerio Ferreira has just kindly supplied a good series of photos of the Angolan springbok (Antidorcas marsupialis angolensis), at https://biodiversidadeangola.com/mammals/scientific/9527.

As it turns out, the darkness of the pygal band and other markings, described by Groves (1981) and used as a partial justification to raise this taxon to full species-status by Groves & Grubb (2011), is not striking. The appearance is, after all, similar to that of subspecies hofmeyri, bearing in mind that even within hofmeyri the specimens from southeastern Botswana were paler than those from Namibia (Groves 1981).

In my view, the possibility that the Angolan springbok is a separate species (Groves & Grubb 2011) has not stood up to scrutiny. And even as a subspecies it is not nearly as distinctive as the black-faced impala (Aepyceros melampus petersi) is from the common impala.

If so, how would this change our overall view of subspecific variation in the springbok?

We can accept that the female horns vary in length along a south-north cline culminating in angolensis. However, clinal variation is not the same as subspeciation. If we assume that the geographical variation in body size and the relative length of the legs is phenotypic as much as genotypic in the springbok, what emerges is a species more noteworthy for its uniformity than for its subspeciation. It seems possible, after all, that the original wild springbok of the Eastern Cape, near Addo, was similar enough (except for the shortness of the female horns) that most naturalists would not have noticed any differences in body size or colouration from the Angolan springbok, 2500 km and 20 degrees of latitude distant.

And what this would mean in turn is that, although Science let the nominate subspecies disappear as a 'pure' entity before it was properly described, Nature may have, as it were, let us off lightly for that lapse.

Posted on May 07, 2021 13:07 by milewski milewski | 0 comments | Leave a comment

May 08, 2021

Similarities and differences: impala vs springbok

The two commonest antelopes in southern Africa are the impala (Aepyceros melampus) and the springbok (Antidorcas marsupialis). Here are some similarities and differences perhaps new to readers.

In flight from predators, both bound high into the air even where there are no obstacles, while being perversely reluctant to jump over fences (instead preferring to crawl under them). However, the impala differs from the springbok in that it neither trots nor stands on its hind legs to reach food.

Both have complex tails with two tracts of erectile fur, unlike any other ungulate. However, in the impala the piloerections are to the side and inwards (ventral), whereas in the springbok the piloerections are outwards (dorsal).

Both have one infant at a time and form creches. However, the impala has a flesh-coloured udder with four teats whereas the springbok has a black-pigmented udder with two. And the hiding period of infants is shorter in the impala than in the springbok, which is the opposite of expectations given that the impala is the more cover-dependent of the two species.

Both use urine and faeces for social communication, with similar postures. However, of the two species the territorial male piles his feces only in the impala.

Both are exceptionally noisy for antelopes in masculine display despite the normal appearance of the larynx; and both can utter their loudest calls while running after rival males (in contrast to deer which roar, bellow or grunt only while standing or walking). However, only the impala intersperses its rutting vocalisations with alarm-snorts.

Both have patterns of colouration similar to gazelles. However, that of the impala has a mainly camouflaging effect, which is odd for a species in which even infants are gregarious. By contrast the colouration of the springbok is more conspicuous than in any of its closest relatives, the true gazelles (Gazella).

Both stot in earnest seemingly only for the painted hunting dog (Lycaon pictus). Both the kick-stotting of the impala and the head-down bouncing of the springbok are styles unique to these species. However, only in the springbok is the same stotting display also performed by the female in courtship.

Posted on May 08, 2021 05:25 by milewski milewski | 0 comments | Leave a comment

May 14, 2021

A comparison of the goitred gazelle and the springbok

Two gazelles, the goitred gazelle (Gazella subgutturosa) of the Iranian region and the springbok (Antidorcas marsupialis) of South Africa, make for an obvious comparison because they live in similar semi-arid grasslands in opposite hemispheres. Adults can hardly hide in these exposed environments. And a puzzling difference in adaptive colouration is that the goitred gazelle tends to blend into its surroundings whereas the springbok tends to stand out even at a distance.

What makes the springbok so conspicuous is its boldly dark flank-band offset by white highlights on the face, rump, flanks and upper legs. In the goitred gazelle the basic pattern is similar but toned down to a semblance of camouflage.

Both species greet scanning predators by stotting displays, but these accentuate the differences. The goitred gazelle merely bounces up and down with its black tail erect. By contrast the springbok has the most extreme bouncing performance seen in any antelope, blazening an uniquely extended white crest which is normally hidden by folds of skin running along the rump.

Consider the different regimes of natural predation in the Iranian region and South Africa. Here, the counterintuitive principle is: the more intense the predation, the more conspicuous the ungulate evolves to be.

In both regions, the natural predators included large cursorial canids (wolf vs painted hunting dog) which scanned the groups of gazelles by day and carefully chose the least-fit member before starting a chase of endurance. This preliminary scrutiny means a selective pressure for self-advertisement ('showing off') instead of keeping a low profile.

A crucial difference was that the northern species was the only wild ruminant in most of its habitat, whereas the southern species coexisted with the red hartebeest (Alcelaphus caama), the blesbok (Damaliscus pygargus phillipsi) and/or the black wildebeest (Connochaetes gnou). The greater reliability of prey in South Africa might have maintained a denser population of predators, thus boosting the risk of any particular group of prey animals being spotted by the painted hunting dog. An evolutionary tipping point may have been reached, flipping the adaptive colouration of adults from concealing to revealing.

The best chance for the individual springbok is not to self-efface, either in the landscape or in the group. Instead it is to announce itself as vitally as possible, disqualifying itself from being worth chasing at all. In the case of the goitred gazelle as for most other antelopes, encounters with predators remained infrequent enough that it made sense to bet-hedge rather than committing to conspicuousness. Red hartebeest, blesbok and black wildebeest also have dark/pale features (bleezes) obvious to predators, but their overall colouration is ambivalent. This may be because all are larger and more enduring in flight than the springbok, and thus less vulnerable to the painted hunting dog.

Posted on May 14, 2021 06:16 by milewski milewski | 0 comments | Leave a comment

May 17, 2021

Introducing the erectile bleeze, one of the most striking features of adaptive colouration in mammals

Various species of ungulates have pale or dark patches on their bodies which are so large that they reveal rather than conceal the whole figure of the animal in its normal surroundings by day. These are usually gregarious species of open vegetation, which have abandoned any attempt to hide as adults and instead find 'safety in numbers' by various means. Perhaps the best example is the springbok (Antidorcas marsupialis), which shows conspicuous white on the rump and, separately, on the flanks.

In a recent Post I suggested that we refer to such bold features, which are likely to be noticeable to scanning predators even when the ungulates stand still, as bleezes. 'Bleeze' is a precise-minded technical variant of the informal and ambiguous words 'blaze' (English) and 'bles' (Afrikaans).

A few species of ruminants take this specialisation further: their bleezes can be expanded by unfolding of the skin and erection of the fur, which produce what I propose we call an 'erectile bleeze'. In the case of the springbok, the anatomy of the skin-folds is so complicated that nobody has yet clearly described it.

The dark-edged white bleeze on the hindquarters, without unfolding and erection, is limited to a diamond shape running from the buttocks to the rump, encompassing the white base of the tail. With full activation this fluffs out, expands fourfold, becomes far more visible in profile, and appears for the first time on the back (see eighth photo in https://ca.finance.yahoo.com/news/springboks-pronking-joy-071753589.html). The word 'crest' falls short because most of the erectile bleeze is a double (left-right) ridge of long fur, parting widely around the tail-base (see sixth photo in https://www.africahunting.com/threads/namibia-namibia-safari-with-kowas-beginning-the-end.11723/page-3) and ending separately on the two buttocks where it has a vertical orientation at right angles to the horizontal orientation seen on the back.

Photos of the springbok can be confusing, because in some instances the unfolding/erection is only partial. For example, the section on the buutocks can be flared without white appearing on the back. And when the animal erects all of its fur after rain, the bleeze may appear 'half-mast'.

Several other species of ruminants, including other genera of gazelles, possess an erectile bleeze on the hindquarters. However, only in the springbok is it the case that the bleeze and the erectile bleeze, although overlapping in anatomical position, are so different in shape and size that the two can hardly be described without resorting to different names.

Posted on May 17, 2021 00:25 by milewski milewski | 0 comments | Leave a comment

Ungulates are surprisingly inept at using their horns against predators

Most species of ungulates have pointed 'weapons' of some kind on their heads, be these horns, antlers or long canine teeth. In males, these are used in fights of rivalry, and in species in which horns or antlers occur also in females they are used for social threats in certain situations. One might, therefore, expect the horns, antlers and teeth of ungulates also to be used to stab when ungulates are attacked by predators.

The surprise is that most species of ungulates turn out to be inept in defending themselves from predators, which means that the pointed structures on their heads function far more as adornments than as weapons; and their deployment is ritual rather than violence.

The problem seems to be that the 'hardware' is not matched by suitable 'software', i.e. the brains of ungulates do not seem to be programmed for adept aiming and striking at the bodies of predators, regardless of how precise their use is in masculine sparring. Ungulates generally rely on rapid flight and reproduction in order for the population to survive predation. When cornered they seem to lack the behavioural versatility to fight in more than a tokenistic way. Once wounded, they go into shock and seem to lose will and coordination.

There seem to be a few exceptions to these generalisations, such as the rocky mountain goat (Oreamnos americanus), black wildebeest (Connochaetes gnou) and muskox (Ovibos moschatus). However, most ungulates with defensive reputations in the semi-popular literature, such as oryxes, are more inept than the fearsome shapes of their horns might suggest. The African buffalo (Syncerus caffer) is certainly dangerous to humans when wounded, but its horns are too blunt to stab an antagonist, and various video-clips show how inept it is versus the lion (Panthera leo) even when there are opportunities to strike blows. The lion is intimated more by the bulk of buffaloes than by the horns as such.

The hook-lipped rhino (Diceros bicornis) is certainly defensive, to the point of seeming aggressive. However it too tends to be inept in actually striking blows, partly owing to incongruously poor eyesight.

It is in the light of this general pattern, in which most ungulates are almost as vulnerable to predators as they would be were their horns absent, that we can understand the basic nature of Spanish bullfighting: choreography rather than a real contest of impalation. The matador pierces the bull, which is incapable of reciprocating - except by accident.

Posted on May 17, 2021 13:10 by milewski milewski | 0 comments | Leave a comment

May 20, 2021

A little-known aspect of the erectile bleeze of the pronghorn

The pronghorn (Antilocapra americana) is a gregarious species of ruminant living in open vegetation. The large patch of whitish on its hindquarters, and broadly whitish flanks, make it conspicuous to scanning predators even at a distance. Upon alarm the fur on the hindquarters is erected to form a disc-like shape, revealing a white so pure that it seems almost luminous.

What is not well-known is that the back-of-neck also contributes to this display. Under certain conditions, a dark patch appears on the back of the neck in conjunction with the erection of the fur on the hindquarters. This can be called a 'mane', but this word fails to do justice to the complexity of the structures (e.g. see https://www.inaturalist.org/observations/36998216, and my comment on that photo).

The mane of the pronghorn is unlike that of any other ungulate. Its peculiarities remain to be fully investigated, but three are relevant here. Firstly, it is more erectile than expected in ruminants, and virtually disappears when fully folded. Secondly, it is proportionately larger in juveniles and females than in adult males. And thirdly, it seems to be activated in two different ways, and their intermediates: vertically erected to a tomahawk-shape or spread sideways into a broad dark patch.

My impression is that the mane of the pronghorn is displayed in different ways by the adult male vs by the female/juvenile. In the former, it is vertically erected (to the tomahawk-shape) as a minor component of display in certain postures of masculine rivalry and courtship. In the female/juvenile, the circumstances of its vertical erection are poorly understood but it seems to be spread laterally as part of anti-predator alarm. This provides a dark-pale contrast otherwise lacking in the overall display, an accentuation consistent with the stotting behaviour shown more by juveniles than adults.

If this interpretation is correct, then I would call the pattern seen in the stotting juvenile a bimodal erectile bleeze. What are added by the erections/activations are the extension of white on the rump and haunches, and extensive darkness on the back-of-neck.

Is there a skin-fold on the nape of the pronghorn, similar to that on the rump of the springbok (Antidorcas marsupialis) albeit smaller and less noticeable to naturalists?

Posted on May 20, 2021 12:54 by milewski milewski | 0 comments | Leave a comment