Adaptive colouration in the bontebok (Damaliscus pygargus pygargus), part 1: adults

Also see https://www.inaturalist.org/journal/milewski/75748-adaptive-colouration-in-the-blesbok-damaliscus-pygargus-phillipsi-part-1-adults#

The bontebok (Damaliscus pygargus pygargus) is one of the most vividly-coloured wild ungulates on Earth.

However, its colouration has not previously been described coherently, relative to a conceptual framework based on adaptation. Furthermore, previous descriptions have been limited by the lack of suitable terms.

A reminder of the difference between a bleeze and a flag:

A bleeze is a large-scale feature of colouration, so bold that it makes the whole figure conspicuous even at a distance, and even when the animal is stationary.

A flag is a relatively small, or normally hidden, feature of colouration, which becomes conspicuous with motion.

The bontebok can be described as 'pied' (https://dictionary.cambridge.org/dictionary/english/pied). However, this is unsatisfactory, because

it does not elucidate the functional organisation of the markings, and
it does not distinguish between an adaptive design and that seen in pied individuals and breeds of domestic mammals (https://en.wikipedia.org/wiki/Piebald).

Various wild ungulates possess bleezes. However, what makes the bontebok unusual is that

it possesses three bleezes,
one of these, viz. the lateral bleeze, occupies the whole side of the torso from the dorsal to the ventral edge, and
consequently, the entire adult figure can be seen as a composite bleeze, i.e. an example of thoroughly conspicuous colouration (https://www.gettyimages.com.br/detail/foto/bontebok-imagem-royalty-free/982765768?adppopup=true).

In this account, I ignore the hues on the pelage of the bontebok, and consider only the tones (white, shades of grey, and black). This is because ungulates and their carnivoran predators do not perceive hues in the same ways as humans do.

OVERALL VIEWS

https://www.shutterstock.com/it/image-photo/walking-field-bontebok-mediumsized-generally-dark-484356043

https://www.inaturalist.org/observations/11251852

https://www.dreamstime.com/bontebok-damaliscus-pygargus-image129038646

https://www.alamy.com/stock-photo-bontebok-damaliscus-pygargus-pygarus-de-hoop-nature-reserve-western-59178463.html?imageid=04F0A152-6CA3-4A65-9067-0364F1A5F09E&p=22059&pn=4&searchId=dca6a568865628209af3d56514ac1f36&searchtype=0

https://www.alamy.com/stock-photo-a-portrait-of-a-bontebok-antelope-in-south-africa-47742290.html?imageid=53CB260B-D3BB-4DD7-B43C-33C570D2CC36&p=158473&pn=1&searchId=abde0ec3b06a08943ffb523ff66f0db0&searchtype=0

https://www.alamy.com/bontebok-damaliscus-pygargus-in-game-park-in-south-africa-looking-over-its-shoulder-image245661564.html

https://www.dreamstime.com/bontebok-damaliscus-pygargus-image129038241

https://www.inaturalist.org/observations/51830740

FACIAL BLEEZE

The conspicuously pale patch on the rostrum of adults of Damaliscus pygargus (https://www.inaturalist.org/taxa/42275-Damaliscus-pygargus) constitutes what is probably the clearest example of a facial bleeze, in any mammal.

In the bontebok, this patch is pure white, contrasting with the dark ground-colour of the face and neck.

https://www.alamy.com/stock-photo-bontebok-blesbok-damaliscus-dorcas-standing-south-africa-47895393.html?imageid=A30EE114-7C91-437B-A4EE-F0E2062F42F1&p=33610&pn=6&searchId=ab384b9287a9a62b3e65ec702d7129d5&searchtype=0

https://www.alamy.com/stock-photo-bontebok-damaliscus-dorcas-at-bontebok-national-park-in-south-africa-38098213.html?imageid=2F8F0D32-30E5-4683-816A-5422AC0E0766&p=60598&pn=2&searchId=595b2aef109e6e3945fa2d85a0f44eb0&searchtype=0

https://www.alamy.com/stock-photo-bontebok-antelope-121112217.html?imageid=C030CB48-025D-450C-9009-14F6598A42A7&p=353301&pn=1&searchId=abde0ec3b06a08943ffb523ff66f0db0&searchtype=0

https://www.gettyimages.com.au/detail/photo/bontebok-damaliscus-dorcas-at-bontebok-national-royalty-free-image/523049311?phrase=bontebok&adppopup=true

https://www.alamy.com/stock-photo-a-pair-of-bontebok-antelopes-damaliscus-pygargus-dorcas-south-africa-85437994.html?imageid=8C3973B1-D533-4CA3-B604-463AAB155B2F&p=70019&pn=1&searchId=abde0ec3b06a08943ffb523ff66f0db0&searchtype=0

There is minimal variation in the facial bleeze, between the sexes, and among individuals. However, a few individuals show slight expansion at the base of the horns (https://www.alamy.com/stock-photo-blesbok-or-bontebok-damaliscus-dorcas-dorcas-syn-damaliscus-pygargus-78567725.html?imageid=967A4632-A630-4F22-84B5-7F50172963C0&p=183822&pn=2&searchId=dff47d9894fdcd82529cde91c8758091&searchtype=0).

Comparison with blesbok (https://www.inaturalist.org/journal/milewski/75748-adaptive-colouration-in-the-blesbok-damaliscus-pygargus-phillipsi-part-1-adults#):

The pale rostral patch on the face seems proportionately slightly smaller in the bontebok than in the blesbok, owing to what I perceive to be a difference in the size of the head.

Furthermore, in the bontebok the pale on the face tends not to expand with age, as it does in the blesbok (https://www.shutterstock.com/it/image-photo/blesbok-antelope-damaliscus-pygargus-standing-grass-1329980789 and https://www.inaturalist.org/journal/milewski/75871-a-previously-overlooked-expansion-of-the-bles-in-the-blesbok-signifying-full-maturity-beyond-adulthood#).

However, the facial bleeze is as well-developed in the bontebok as in the blesbok, because it seems exempt from the glandular staining seen in males of the blesbok (https://www.alamy.com/a-blesbok-antelope-damaliscus-pygargus-south-africa-image66899227.html?imageid=AA000BC4-7506-4457-96A0-B91FB81FCF46&p=70019&pn=1&searchId=a83f931787d9571cb0a25aca9f82d745&searchtype=0 and https://www.alamy.com/stock-photo-portrait-of-a-blesbok-antelope-damaliscus-pygargus-south-africa-59076858.html?imageid=9FB1F37F-B684-4FE4-A0A4-9A9AC4C55B63&p=70019&pn=1&searchId=a83f931787d9571cb0a25aca9f82d745&searchtype=0).

LATERAL BLEEZE

The lateral bleeze of the bontebok is, proportionately, one of the largest bleezes seen in any ungulate. It extends from the withers and the back to the ventral edge of the thorax and the belly. It also Includes the posterior surface of the upper foreleg, and the anterior surface of the hindleg just below the knee (https://www.inaturalist.org/observations/3985830 and https://www.inaturalist.org/observations/38720040).

The pattern is one of horizontal banding on a broad design, in which the upper and lower panels are pale, with the flanks forming a dark median panel.

However, an important qualification is that the upper panel appears pale partly owing to sheen. Its conspicuousness thus depends on illumination.

https://www.dreamstime.com/stock-photo-bontebok-field-looking-perfect-medium-sized-generally-dark-brown-antelope-prominent-wide-white-image77512668

https://www.agefotostock.com/age/en/details-photo/bontebok-damaliscus-dorcas-dorcas-de-hoop-reserve-south-africa-africa/RHA-743-243/1

https://www.agefotostock.com/age/en/details-photo/bontebok-damaliscus-dorcas-dorcas-bovidae-antelope-mammal-animal-cape-of-good-hope-national-park-south-africa-africa/H44-10978980/1

https://www.alamy.com/stock-photo-bontebok-damaliscus-pygargus-pygarus-at-the-base-of-the-langeberg-59175692.html?imageid=FE1F6904-9478-4A53-8A24-5E8D481C7E90&p=22059&pn=3&searchId=6d8a7f95c3b92935b5e8c1d5d07d00ff&searchtype=0

https://www.alamy.com/bontebok-in-the-bontebok-national-park-swellendam-western-cape-south-africa-image342638387.html?imageid=5C55BBE5-4514-4B34-AEDA-ACC05175FD68&p=22337&pn=3&searchId=6d8a7f95c3b92935b5e8c1d5d07d00ff&searchtype=0

https://www.inaturalist.org/observations/113481398

https://www.inaturalist.org/observations/115575412

https://www.inaturalist.org/observations/80586175

https://www.alamy.com/stock-photo-bontebok-antelope-114770771.html?imageid=0A5EB348-1301-4DC3-B4AD-F99E5785ACEA&p=353301&pn=4&searchId=29c543d132619cf1217ce0a23a3945c6&searchtype=0

https://www.gettyimages.com.au/detail/photo/bonteboks-grazing-royalty-free-image/541049632?phrase=blesbok&adppopup=true

The design of the lateral bleeze of the bontebok is such that in bright sunlight at midday, when the ventral white is inconspicuous owing to shading, the dorsal sheen is 'switched on' owing to sheen (https://www.inaturalist.org/observations/27337501 and https://www.inaturalist.org/observations/27289820).

Comparison with blesbok:

A categorical difference is that, unlike the bontebok, the blesbok lacks a lateral bleeze.

The pelage of the flanks is not necessarily any paler in the blesbok than in the bontebok. However, the differences are that, in the blesbok,

the dorsal sheen is poorly-developed,
the pale ventral pelage is restricted, and reduced to a combination of countershading and an abdominal flag, and
the white anterior edge of the hindleg, just below the knee, is narrower than in the bontebok.

Furthermore,

the abdominal flag of the blesbok (https://www.inaturalist.org/observations/130975314) does not occur in the bontebok, having been subsumed within a broader white, ventral panel, and
the ulnar flag of the blesbok does not occur in the bontebok, the dark/pale contrast on the posterior surface of the upper foreleg - although just as clear - functioning as an anterior extension of the ventral white of the thorax (and thus being better-regarded as part of the lateral bleeze) in the bontebok.

ISCHIOPYGAL BLEEZE

The ischiopygal bleeze of the bontebok is about as large as the facial bleeze, but located at the opposite pole of the figure (https://www.alamy.com/stock-photo-a-pair-of-bontebok-antelopes-damaliscus-pygargus-dorcas-south-africa-85437994.html?imageid=8C3973B1-D533-4CA3-B604-463AAB155B2F&p=70019&pn=1&searchId=abde0ec3b06a08943ffb523ff66f0db0&searchtype=0 and https://www.dreamstime.com/stock-photo-bontebok-antelopes-pair-damaliscus-pygargus-dorcas-south-africa-image56821286).

The pale posterior feature of the bontebok

extends from the rump to the tail-stalk and the buttocks,
is largely white, and
contrasts with the dark pelage around it.

https://www.inaturalist.org/observations/80650367

https://www.inaturalist.org/observations/57714646

https://www.alamy.com/stock-photo-a-bontebok-damaliscus-pygargus-in-the-bontebok-national-park-near-173731691.html?imageid=75A1E59F-9E57-44B2-8852-46B50B30641E&p=77702&pn=6&searchId=d7a105eea18d32dc6155ddf3de390174&searchtype=0

https://www.inaturalist.org/observations/53977868

Comparison with blesbok:

The ischiopygal flag of the blesbok bears the same relationship to the ischiopygal bleeze of the bontebok as the abdominal flag of the blesbok (https://www.alamy.com/blesbok-in-savannah-south-africa-image151809725.html?imageid=3B900166-AC81-4937-96B6-1CA462655F62&p=703420&pn=10&searchId=26e0b007d6f642f3bb26a9cc6900a5cf&searchtype=0) bears to the white ventral panel of the lateral bleeze of the bontebok.

Furthermore, the ischiopygal flag of the blesbok depends mainly on sheen effects, whereas the ischiopygal bleeze of the bontebok depends mainly on the depigmentation of the pelage.

PEDAL FLAG

The lower legs of adults of the bontebok are largely white, making them conspicuous in locomotion.

https://www.inaturalist.org/observations/127885416

https://www.dreamstime.com/stock-photo-bontebok-antelope-running-velt-image65832109

https://www.alamy.com/bontebok-are-the-colourful-bok-of-south-africa-image228097057.html?imageid=7AAA4F55-17D1-423B-BF91-57470077439F&p=641396&pn=1&searchId=25869b8bb63848eab5bc67f94e53a679&searchtype=0

https://www.alamy.com/stock-photo-bontebok-antelope-17066360.html?imageid=AFA96455-2E25-41C8-91B0-1B7B94A1EA3C&p=4877&pn=1&searchId=abde0ec3b06a08943ffb523ff66f0db0&searchtype=0

https://www.alamy.com/stock-photo-bontebok-antelope-17066531.html?imageid=87C5DBB8-BEBE-41B5-A483-7EF7427CDD10&p=4877&pn=3&searchId=8e369419b3a055a70321251ed7501637&searchtype=0

Comparison with blesbok:

Both the bontebok and the blesbok possess a pedal flag. However, this feature is better-developed in the bontebok, in which

the white pelage is more extensive, particularly on the outer surfaces of the lower legs, and
there is less individual variation.

LACK OF AURICULAR FLAG

In the bontebok, there is a considerable sheen on the short, sparse pelage on the posterior surface of the ear pinnae. In some.views this produces a noticeably pale aspect to the back-of-ear.

However, after perusing hundreds of photos, I have not found this effect to be strong or consistent enough to qualify as an auricular flag. It is better-regarded as an incipient/residual version of the pattern in the blesbok (see below).

https://www.agefotostock.com/age/en/details-photo/bontebok-antelope/ESY-001254401/1

https://www.alamy.com/bontebok-antelope-damaliscus-pygargus-dorcas-south-africa-image156518411.html?imageid=FCBE4CA1-DBF7-4706-9D07-20EC04F83E25&p=476215&pn=1&searchId=abde0ec3b06a08943ffb523ff66f0db0&searchtype=0

https://www.inaturalist.org/observations/84604329#data_quality_assessment

https://www.alamy.com/stock-photo-bontebok-antelope-bontebok-national-park-swellendam-overberg-western-139221333.html?imageid=C6DAAADA-77BC-4140-AC0F-6ACCCDFABC9D&p=10587&pn=1&searchId=abde0ec3b06a08943ffb523ff66f0db0&searchtype=0

https://www.alamy.com/stock-photo-at-the-peaceful-and-quiet-bontebok-south-african-park-two-antelopes-32166159.html?imageid=143BD930-B2D0-433C-A84D-753F5F9CE194&p=94763&pn=1&searchId=abde0ec3b06a08943ffb523ff66f0db0&searchtype=0

https://www.inaturalist.org/observations/115550547

https://www.alamy.com/bontebok-walking-image647406.html?imageid=FF50FFAE-284D-4D2A-B72E-56FEB151968F&p=4877&pn=4&searchId=29c543d132619cf1217ce0a23a3945c6&searchtype=0

Comparison with blesbok:

The ear pinnae seem identical in size and pigmentation in the bontebok and the blesbok.

However, perusal of hundreds of photos shows that the sheeny quality of the posterior surface is better-developed in the blesbok (https://www.agefotostock.com/age/en/details-photo/blesboks-damaliscus-pygargus-phillipsi-two-adults-standing-in-open-grassland-alert-mountain-zebra-national-park-eastern-cape-south-africa-africa/ZI6-3207754/1 and https://www.agefotostock.com/age/en/details-photo/bontebok-south-africa/FHR-88889-04144-075/1) than in the bontebok.

This, together with the distraction presented by the relatively well-developed sheen on the withers and back, disqualifies the bontebok, in my view, for an auricular flag (https://www.inaturalist.org/journal/milewski/75905-unlike-the-blesbok-the-bontebok-damaliscus-pygargus-pygargus-lacks-an-auricular-flag#).

The lack of an auricular flag in the bontebok is significant evolutionarily. This is because all of the postcranial pale features are better-developed in the bontebok than in the blesbok.

LACK OF CAUDAL FLAG

Please see https://www.inaturalist.org/journal/milewski/79845-in-the-adaptive-colouration-of-genus-damaliscus-is-there-a-caudal-flag#.

DISCUSSION

The colouration of adults of the bontebok is configured in such a way that the figure is conspicuous, regardless of whether