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

Also see https://www.inaturalist.org/journal/milewski/76311-adaptive-colouration-in-the-bontebok-damaliscus-pygargus-pygargus-part-1-adults#

The colouration of the blesbok (Damaliscus pygargus phillipsi) is complex and subtle. Its description depends on a clear lexicon.

I have, therefore, introduced a set of suitable terms, such as 'bleeze' and 'flag' (please see https://www.inaturalist.org/journal/milewski/70293-the-bambis-part-9-bleezes-flags-and-semets-in-the-bovid-genus-raphicerus#).

The blesbok is sexually dimorphic in body-form, but sexually monomorphic in colouration, apart from the paleness of the horns of males (https://www.istockphoto.com/photo/blesbok-antelope-gm176740530-26373055?phrase=pics%20of%20a%20blesbok and https://www.istockphoto.com/photo/blesbok-antelope-grooming-gm120525871-16006166?phrase=pics%20of%20a%20blesbok).

However, the blesbok emphasises ontogenetic differences. It is unusually complex in the changes in its colouration from birth to full maturity.

OVERALL VIEWS

The following are among the clearest photos ever taken of the colouration of adults of the blesbok:

Adult males:

https://stock.adobe.com/au/images/blesbok-damaliscus-pygargus-phillipsi-or-blesbuck-male-full-body-portrait-highly-focused-in-summer-south-africa/316662322

https://www.agefotostock.com/age/en/details-photo/a-blesbok-antelope-damaliscus-pygargus-south-africa/ESY-033886226

https://upload.wikimedia.org/wikipedia/commons/8/84/Blesbok%2C_Damaliscus_pygargus_phillipsi%2C_at_Krugersdorp_Game_Reserve%2C_Gauteng%2C_South_Africa_%2826872993194%29.jpg

https://www.shutterstock.com/it/image-photo/blesbok-antelope-mountain-zebra-national-park-126157481

Adult females:

https://www.istockphoto.com/photo/blesbok-antelope-gm144341776-4192140?phrase=pics%20of%20a%20blesbok

https://www.inaturalist.org/observations/9305447

FACIAL BLEEZE

The whitish patch on the rostrum of adults of the blesbok is so bold (https://www.inaturalist.org/observations/51745997) that it makes the whole figure conspicuous, even at distance and even when stationary (https://www.alamy.com/stock-photo-herd-of-blesbok-in-field-africa-87078020.html?imageid=86BEBDEB-C18F-4079-8D07-AFF1F8FF92C7&p=269694&pn=1&searchId=34a5985d254a7cecee5d7188055b6b4c&searchtype=0).

This not only activates the auricular flag (see below), but also means that the facial bleeze may double as a facial flag.

The following show the facial bleeze of the blesbok particularly clearly.

AURICULAR FLAG

The posterior surface of the ear pinnae is greyish, apparently by virtue of dark skin covered only partly by short, whitish pelage (https://www.inaturalist.org/observations/98624681 and https://www.inaturalist.org/observations/8679095 and https://www.istockphoto.com/photo/blesbok-in-tall-grass-gm598058408-102466865?phrase=pics%20of%20a%20blesbok and https://www.dreamstime.com/royalty-free-stock-photos-blesbuck-green-veld-male-standing-grassy-image36500088).

However, this pelage is sheeny, and usually appears pale enough to be conspicuous. This is accentuated by the movements of the ear pinnae.

For illustrations, please see https://www.inaturalist.org/journal/milewski/75905-unlike-the-blesbok-the-bontebok-damaliscus-pygargus-pygargus-lacks-an-auricular-flag#.

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#

ISCHIOPYGAL FLAG

There is a small extent of whitish pelage at the base of the tail-stalk, plus narrowly on the immediately adjacent, uppermost buttocks (https://www.inaturalist.org/observations/32952118 and https://www.istockphoto.com/photo/blesbok-standing-in-the-green-grass-in-nkomazi-game-reserve-gm1249613271-364226795?phrase=pics%20of%20a%20blesbok and https://www.istockphoto.com/photo/blesbok-antelope-gm1461358012-495340823?phrase=pics%20of%20a%20blesbok and https://www.istockphoto.com/photo/blesbok-or-blesbuck-antelope-gm1324694272-409947632?phrase=pics%20of%20a%20blesbok and https://www.istockphoto.com/photo/blesbok-on-the-high-plains-of-mountain-zebra-national-park-gm161659578-23057114?phrase=pics%20of%20a%20blesbok and https://www.inaturalist.org/observations/37693385 and https://www.inaturalist.org/observations/21091815).

The brown pelage on the rump, adjacent to the base of the tail, is remarkably sheeny, and possibly also reflects ultraviolet light. This surface is conspicuous, dependent on illumination.

In the following view (https://www.agefotostock.com/age/en/details-photo/bontebok-damaliscus-dorcas-dorcas-three-adults-standing-in-habitat-mountain-zebra-n-p-eastern-cape-south-africa/FHR-10018-00071-249/1), the three individuals vary in the extent of whitish near the base of the tail. I suggest that this is owing to the angle of illumination, rather than individual differences in the extent of depigmentation.

The pale conspicuousness centred at the base of the tail is not particularly dependent of any contrast with the dark of the tail-tassel and tail-stalk (https://www.dreamstime.com/royalty-free-stock-photos-curious-antelope-looking-back-image19998398 and https://upload.wikimedia.org/wikipedia/commons/1/1f/Blesbok%2C_Damaliscus_pygargus_phillipsi%2C_at_Krugersdorp_Game_Reserve%2C_Gauteng%2C_South_Africa_%2827205054520%29.jpg and https://www.gettyimages.com.au/detail/photo/blesbok-royalty-free-image/1351086134?phrase=blesbok&adppopup=true).

https://www.inaturalist.org/observations/7916986
https://www.inaturalist.org/observations/11153973
https://www.inaturalist.org/observations/146248363
https://www.mediastorehouse.com.au/ardea-wildlife-pets-environment/wat-9970-1310432.html

The following shows that the dark tail-tassel can indeed provide dark/pale contrast for the ischiopygal flag (https://www.alamy.com/blesbok-damaliscus-phillipsi-damaliscus-dorcas-phillipsi-damaliscus-pygargus-phillipsi-standing-in-savanna-south-africa-eastern-cape-mountain-zebra-national-park-image255390768.html?imageid=2191134B-223A-4F72-9776-0F9F1267384F&p=851122&pn=1&searchId=34a5985d254a7cecee5d7188055b6b4c&searchtype=0).

ULNAR FLAG (also see https://www.inaturalist.org/journal/milewski/67086-adaptive-colouration-in-the-common-eland#)

There is a distinct, sharply-defined pattern of dark/pale on the posterior surface of the upper foreleg (https://www.inaturalist.org/observations/19660890).

This is most conspicuous in posteriolateral view, and works in conjunction with the abdominal flag (https://www.flickr.com/photos/dorneyphoto/49990958018/in/photolist-2jawJah-Hg63fU-bpxo9b-akqXjc-kDZnJt-8UcSMq-Sgocj4-2hdX4hz-2hRvAAH-2nqxXKA-2k7THja-2nFTwAK-NtcqZw-2mKwoFx-K9H7kw-2nYaeMv-2jbEesL-2jbJeMK-NwubQy-FGdmr3-CMZ9sW-2mVjjPf-ThNHJU-21La8WY-8xnKqU-eMntC3-KA9iEt-2kYpdSu-bsgrmu-2jxYMd5-b3zx7T-2hQhV25-jyHrKJ-2k5VFg7-5sqULW-2fkJEYZ-2kPChVk-21DVXBL-dRVYii-2kvQbEc-yRBxjS-EjKxsR-7cWLgq-21oyHh4-oD1wzM-eijdtU-2gmKAXS-7y3c7F-frYRFL-MdmiNW).

ABDOMINAL FLAG

The pale on the ventral surface of the thorax of the blesbok conforms to countershading. However, that on the abdomen (the bulge of the belly) is relatively extensive, reaching high enough to catch the light in certain illuminations (https://www.inaturalist.org/observations/13007113).

This patch of whitish contrasts with the dark of the posterior flanks (https://www.shutterstock.com/it/image-photo/blesbok-standing-grasslands-staring-camera-116258029).

https://www.dreamstime.com/royalty-free-stock-photo-blesbok-blesbuck-damaliscus-pygargus-phillipsi-antelope-endemic-to-south-africa-has-distinctive-white-face-forehead-which-inspired-image29787325
https://www.alamy.com/stock-photo-a-blesbok-antelope-damaliscus-pygargus-south-africa-55200316.html
https://www.inaturalist.org/observations/66931367
https://www.dreamstime.com/stock-images-two-blesbok-image24725644
https://www.istockphoto.com/photo/blesbuck-in-afternoon-light-gm142312104-19664384?phrase=pics%20of%20a%20blesbok

The abdominal flag remains visible when the animal is lying down (https://www.inaturalist.org/observations/56204464 and https://www.inaturalist.org/observations/21633734).

PEDAL FLAG

The lower legs of the blesbok have pale tracts, particularly on the inner surfaces. On the forelegs, the pale pelage includes the carpal joint.

This depigmentation makes the lower legs conspicuous in certain circumstances, particularly during walking.

DISCUSSION

When the facial bleeze is not in full view, the colouration of the blesbok is not conspicuous at a distance (https://www.inaturalist.org/observations/7677767). In this way, the blesbok differs from
coexisting gregarious ruminants, particularly

Antidorcas marsupialis (thoroughly conspicuous colouration), and
Connochaetes gnou (whole figure conspicuously dark, https://www.shutterstock.com/it/video/clip-4203871-black-wildebeest-blesbok-antelopes-gathering-waterhole-south and https://www.alamy.com/black-wildebeest-and-blesbok-in-southern-african-savannah-image379298498.html and https://www.flickr.com/photos/66652931@N07/37895595624 and https://www.canstockphoto.com/wildebeest-and-antelopes-at-a-water-14562558.html and https://www.travelblog.org/Photos/7968590).

Alcelaphus caama, which also coexists with the blesbok, is similar in that its conspicuousness at a distance depends on a single bleeze. However, in the case of this hartebeest, the bleeze is on the hindquarters, not on the face (https://www.inaturalist.org/observations/18412391).

Skinner and Chimimba (2005), on page 656, state: "The characteristic habit of standing in orientated groups with their heads towards the sun and their faces close to the ground is common to both blesbok and bontebok. Authorities differ as to whether they are indeed sleeping in this posture or not. They occasionally indulge in violent head-shaking, snorting or stamping of feet and then run in a small circle to resume their places in the group."

It is intriguing to consider the implications of this behaviour in terms of facial and pedal flagging.

In particular, it seems possible that, when standing gregariously in the bright light of midday, the blesbok hides its facial bleeze from scanning predators (historically, Lycaon pictus).

https://www.istockphoto.com/photo/blesbuck-standing-in-field-with-head-down-mpongo-game-reserve-gm535723433-57297208

All of the conspicuous features of the blesbok are pale. However, some depend more on sheen than on depigmentation.

The auricular flag and the ischiopygal flag are largely dependent on sheen effects. By contrast, the facial bleeze, ulnar flag, and abdominal flag have no detectable component of sheen, the pelage being simply whitish.

In the case of the pedal flag (https://www.shutterstock.com/it/image-photo/early-morning-blesbok-full-body-shot-91405364), the situation is complicated by individual variation and possibly the age of adults. Therefore, further scrutiny is needed to resolve the role of sheen.

ADDITIONAL MATERIAL

https://www.britannica.com/animal/blesbok

https://777ranch.com/product/blesbok-or-blesbuck/

https://animalia.bio/blesbok

https://www.gettyimages.com.au/detail/photo/blesbok-break-royalty-free-image/595653629?phrase=blesbok&adppopup=true

https://www.gettyimages.com.au/detail/photo/group-of-blesbok-resting-on-the-plains-eastern-cape-royalty-free-image/1371293427?phrase=blesbok&adppopup=true

https://www.gettyimages.com.au/detail/photo/blesboks-royalty-free-image/74077088?phrase=blesbok&adppopup=true

https://www.shutterstock.com/it/image-photo/pair-blesboks-blesbucks-vicinity-pretoria-damaliscus-497011051

https://www.shutterstock.com/it/image-photo/blesbok-antelope-damaliscus-pygargus-standing-grassland-188464454

https://www.lookphotos.com/en-us/images/71039682-Two-blesbok-Damaliscus-pygargus-phillipsi-Mountain-Zebra-National-Park-South-Africa-Africa

https://myloview.com/wall-mural-a-blesbok-antelope-damaliscus-pygargus-in-natural-habitat-no-5626EF6

To be continued in https://www.inaturalist.org/journal/milewski/75995-adaptive-colouration-in-the-blesbok-damaliscus-pygargus-phillipsi-part-2-infants-juveniles-and-adolescents#...