Adaptive colouration in wildebeests, part 2: facial, nuchal, caudal, and pedal flags

...continued from https://www.inaturalist.org/posts/54094-adaptive-colouration-in-wildebeests-part-1-an-introduction-to-large-scale-conspicuous-features#

(The distributions of forms of Connochaetes can be seen in https://www.researchgate.net/figure/Map-showing-the-distribution-of-wildebeest-subspecies-in-Africa-including-some-important_fig2_305317918 ; mattosi occupies the western, major lobe of the blue area, in Botswana, Namibia, Zambia, and Angola.)

We have seen that the overall colouration of wildebeests (Connochaetes) is ambivalent in terms of the distinction between adaptive conspicuousness and adaptive inconspicuousness.

The overall figure is darkest in gnou, taurinus, mearnsi, and mattosi, intermediate in johnstoni, and palest in albojubatus and cooksoni. In the former four forms, the figure is dark enough to be conspicuous at a distance even while stationary.

The following nicely illustrate the adaptive conspicuousness, in the form of overall darkness, in
mearnsi: https://www.dreamstime.com/stock-photo-lioness-savannah-national-park-kenya-tanzania-masai-mara-serengeti-excellent-illustration-image79105582 and https://www.itripcoltd.com/serengeti-national-park/.

No form of wildebeest is conspicuously pale overall. Furthermore, all of the pale features seen in the various forms are variable according to individual, age, soiling (particularly by dust), perspective, and illumination.

However, the following parts of the body are potentially pale enough to be adaptively conspicuous:

  • restricted patches on the front and/or sides of the face,
  • the beard,
  • the base of the mane, from crown to withers,
  • the rump, extending to the back, and
  • the long hairs of the tail.

How should we categorise the various conspicuous features of colouration in Connochaetes?

A BLEEZE is a feature of dark/pale contrast, large enough to reveal the whole stationary figure at the range relevant to scanning predators. This is epitomised by Damaliscus pygargus pygargus (https://www.krugerpark.co.za/africa_bontebok.html).

A FLAG is a relatively small dark, pale, or dark-and-pale feature that becomes conspicuous to scanning predators once the body-part concerned is moved.

There is no clear example of a bleeze in wildebeests. This is because the pale features are not large enough or consistently pale enough to be reliably conspicuous in the stationary figure.

However, in several forms, an effect similar to that of a bleeze is potentially created by the sheen on the rump, in bright sunlight near midday. This may possibly have an ultraviolet component.

The following illustrates the pale rump in mearnsi:
https://www.theverge.com/2016/2/28/11120948/the-verge-review-of-animals-the-wildebeest and https://es.123rf.com/photo_64207434_herd-of-blue-wildebeest-connochaetus-taurinus-seen-from-behind-during-migration-serengeti-national-p.html?vti=undefined-1-60 and sixth photo in http://blog.jeffcable.com/2021/09/photos-of-great-migration-wildebeests.html and https://www.gettyimages.com.au/detail/photo/wildebeest-herds-royalty-free-image/200289836-001?phrase=antilope%20sp&adppopup=true and https://www.gettyimages.com.au/detail/news-photo/blue-wildebeest-or-white-bearded-wildebeest-bovidae-news-photo/492753635?adppopup=true.

In wildebeests, several categories of flags occur:

  • facial (on the front and/or sides of the head, extending to the beard; these are further examined in part 3),
  • nuchal (on the dorsal part of the neck and the withers, i.e. involving the mane),
  • caudal (on the tail and its base), and
  • pedal (on the feet; evidence for a pedal flag in infants/juveniles of wildebeests will appear in part 5.)

FACIAL FLAG:

A facial flag is present in albojubatus (also see part 3), and ambivalently present in mearnsi and cooksoni.

The following illustrates albojubatus, in which the front of the face is black, and the cheeks and beard are pale: https://www.flickr.com/photos/gridarendal/31251992874 and https://www.kimballstock.com/preview.asp?db=a&image=AFW+03+MH0029+01.

This flag is configured in such a way that the paleness of the beard can be most obvious when that of the cheek is shaded: https://www.flickr.com/photos/jozioau/22700271251/.

The beard is not pale enough in mearnsi (see https://www.flickr.com/photos/olegchernyshov/36294975016/ and https://www.fotosearch.com/CLT005/kz5444/) to qualify as a facial flag, except when backlit (https://www.gettyimages.com.au/detail/photo/kenya-masai-mara-wildebeest-migrating-royalty-free-image/200026827-001?phrase=antilope%20sp&adppopup=true and https://www.inaturalist.org/observations/38738619 and https://www.flickr.com/photos/davidbygott/39917897804 and https://www.inaturalist.org/observations/50780031).

The dark surfaces of the face and throat are expanded, in gnou, by dark tufts and a dark beard (https://trek.zone/en/south-africa/animals/black-wildebeest and https://www.shutterstock.com/image-photo/close-black-wildebeest-reveals-long-eyelashes-1186075528). In the case of mattosi, the dark beard is particularly well-developed (https://animals.fandom.com/wiki/Blue_Wildebeest?file=Blue_Wildebeest.jpg).

However, in neither case is dark/pale contrast involved in these adornments. Therefore, these forms do not qualify for facial flags (except possibly in the case of infants of mattosi).

The case for a facial flag in johnstoni rests mainly on the whitish bar across the rostrum (see http://www.africahunting.com/hunting-pictures-videos/showphoto.php?photo=10621&title=nyasaland-gnu-in-tanzania&cat=506 and https://realorasafaris.co.za/product/wildebeest-nyasa/). However, this is too inconsistently to qualify.

NUCHAL FLAG:

The clearest example of a nuchal flag occurs in gnou (see part 1 for illustrations).

In mattosi, some individuals, in certain illuminations, show pale along the base of the mane: https://www.gettyimages.com.au/detail/news-photo/wildebeest-wildebeest-picture-taken-in-etosha-national-park-news-photo/157890493?phrase=antilope%20sp&adppopup=true.

In albojubatus, the withers are so pale (partly owing to sheen) that, in certain illuminations, they contrast with the lax, black mane: https://www.alamy.com/one-single-1-lonely-wild-gnu-wildebeest-population-amboseli-kenya-image6726874.html.

CAUDAL FLAG:

The tail is so large that all forms of wildebeest probably qualify for a caudal flag (e.g. see taurinus https://www.shutterstock.com/nb/image-photo/this-running-wildebeest-photographed-sunrise-etosha-1667738122).

However, the case is strengthened in albojubatus and cooksoni, in which the blackish of the swishing tail contrasts in certain illuminations with the particularly pale and sheeny hindquarters (see https://www.gettyimages.com.au/detail/photo/white-bearded-wildebeest-royalty-free-image/1308653007?adppopup=true and https://www.gettyimages.com.au/detail/photo/wildebeest-running-in-the-landscape-of-amboseli-royalty-free-image/1174138809?adppopup=true and http://www.birdphotographers.net/forums/showthread.php/29883-Cookson-s-Wildebeest-on-the-run).

The simplest example of a caudal flag occurs in gnou, in which the long hairs of the tail tend to be noticeably pale. The following, of all the photos on the Web, perhaps shows this feature most clearly: https://www.flickr.com/photos/cirdan-travels/40444840683.

The tail-tassel of this species is usually far from white (possibly owing to dust).

However, it is large enough to be conspicuous (and probably audible) at distance when swished (see https://www.alamy.com/stock-photo-bucking-black-wildebeest-or-white-tailed-gnu-connochaetes-gnou-etosha-74615399.html and https://www.inaturalist.org/observations/9552228 and https://www.inaturalist.org/observations/41123029 and https://www.alamy.com/stock-photo-black-wildebeest-connochaetes-gnou-female-with-calf-on-grass-111520091.html and https://www.gettyimages.com.au/detail/photo/side-view-of-buffalo-standing-on-field-otavi-royalty-free-image/1320030695?adppopup=true).

This would be enhanced with backlighting (https://www.alamy.com/black-wildebeest-white-tailed-gnu-connochaetes-gnou-running-mountain-image65490820.html?imageid=78425E5F-E183-4673-930D-EA92464E99CF&p=94604&pn=1&searchId=4227aef649dce5ec668f0e5deae5470a&searchtype=0).

For further views of the conspicuously pale tail of gnou, please see:
https://www.alamy.com/black-wildebeest-crosses-gravel-pan-swishing-tail-image402457272.html?imageid=56A76549-DD31-4D7E-8D8D-EE877A22BA85&p=340116&pn=1&searchId=b4c10b7981aa8c3de07682b01860668d&searchtype=0 and https://www.alamy.com/stock-photo-black-wildebeest-white-tailed-gnu-connochaetes-gnou-stands-in-savanna-120487997.html and https://www.shutterstock.com/image-photo/black-wildebeest-southern-african-savanna-641891347 and https://www.dreamstime.com/stock-photo-black-wildebeest-white-tailed-gnu-connochaetes-gnou-riet-was-once-extinct-its-recovery-conservation-success-image71329978 and https://www.agefotostock.com/age/en/details-photo/black-wildebeest-white-tailed-gnu-connochaetes-gnou-runs-across-the-savanna-south-africa-eastern-cape-mountain-zebra-national-park/BWI-BS421486 and https://www.facebook.com/GiraffeHouseWildlifeCentre/photos/a.550406621678028/1327307043987978/.

The following illustrate the caudal flag in albojubatus: https://www.alamy.com/blue-wildebeest-connochaetes-taurinus-amboseli-national-park-kenya-image62676623.html.

PEDAL FLAG:

Please see part 5 of this series.

to be continued in https://www.inaturalist.org/posts/54111-adaptive-colouration-in-wildebeests-part-3-focussing-on-the-facial-flag#...

Posted on July 09, 2021 05:36 AM by milewski milewski

Comments

Yes, indeed, the wildebeest's adaptation in this regard is magnificent; however, how does the dark hue that works so well in so many regards not also work like a heat magnet and hot water storage tank for the sun's rays in a desert that can be blistering hot. When in a sun-soaked desert, I try to avoid wearing (harder to detect) dark shades, especially like in the form of a thick fur coat, and instead opt for (highly visible) light colors that reflect the sun's rays. so I don't overheat or cook myself. Ruth

Posted by grinnin about 3 years ago

Ruth, you have asked an insightful question. It is true that a problem with the overall darkness of the black wildebeest, the western white-bearded wildebeest, and the blue wildebeest is the risk of overheating. There is at least one publication on this: https://pubmed.ncbi.nlm.nih.gov/25436964/. The authors found that the black wildebeest manages to stay out in the sun even at the hottest times, whereas the blue wildebeest seeks shade. They interpret this partly in terms of the thicker, more insulating fur of the black wildebeest. However, I was a bit amused to see that they assume the coat-colour of the black wildebeest to be black, whereas it is actually medium brown. I see this as another example of cognitive dissonance, along the lines that if the name says black then the mind does not even register it when the eyes see medium brown. Putting that paper aside and thinking your question through from scratch: I suggest that a main way in which all the conspicuously dark forms of wildebeest avoid absorbing too much sunlight is by means of sheen/antisheen, i.e. the reflective quality of the hairs resulting from structural features of the hairs as opposed to pigmentation. This is roughly in the same category of phenomena as 'invisibility cloaks'. The light hitting a black hair is absorbed and converted to heat. But the light hitting a wildebeest's hair is largely reflected by a complex physical structure involving a concave cross-section and certain tiny scale-like textures on the surface of each hair. When the reflected light reaches our eyes, we call it sheen, e.g. the car bonnet-like shine on the rump. When the reflected light misses our eyes, we see the surface as blackish, which is what I call antisheen. But the important points are a) that dark wildebeests are not nearly as pigmented as they may seem, and b) they have configured the fur to solve two problems in one solution: the sheen/antisheen both reduces heating and gives these animals the adaptive conspicuousness that suits them for social communication and a 'showoff' approach to anti-predation. And, to round it off, having somewhat dark pigmentation helps them to hide at night out in the open, from the eyes of their predators, to a degree which would not have been possible had they solved their thermoregulatory problems by being depigmented. Does any of this make sense?

Posted by milewski about 3 years ago

PEDAL FLAG IN INFANTS

Connochaetes albojubatus:

https://es.123rf.com/photo_62252521_mother-and-baby-wildebeest-in-amboseli-park-kenya.html

https://twitter.com/FossilRim/status/1341504388863541248/photo/4

https://www.gettyimages.com.au/detail/news-photo/boston-ma-a-baby-wildebeest-born-in-the-past-week-on-news-photo/1371566822?phrase=baby%20wildebeest&adppopup=true

https://www.gettyimages.com.au/detail/news-photo/boston-ma-a-baby-wildebeest-born-in-the-past-week-on-news-photo/1371566810?phrase=baby%20wildebeest&adppopup=true

Connochaetes taurinus mattosi:

https://www.mindenpictures.com/stock-photo-blue-wildebeest-connochaetes-taurinus-cow-with-calf-deception-valley-naturephotography-image00425240.html

https://www.gettyimages.com.au/detail/news-photo/wildebeest-mother-is-nursing-a-newly-born-baby-on-the-news-photo/1199698485?phrase=baby%20wildebeest&adppopup=true

Connochaetes mearnsi:

https://www.alamy.com/stock-photo-baby-blue-wildebeest-or-brindled-gnu-connochaetes-taurinus-with-its-135203665.html?imageid=4442E245-846C-4DC8-8D0B-EC7A7C9484BC&p=38682&pn=1&searchId=4093b7b4151429bdd59b4c6faf51ee5c&searchtype=0

https://www.alamy.com/a-newborn-blue-wildebeest-brindled-gnu-connochaetes-taurinus-nursing-in-serengeti-national-park-tanzania-east-africa-africa-image374626149.html?imageid=F2C3F5C9-B440-4C40-923B-A9493124DE06&p=196854&pn=1&searchId=0d1226817328860847233070d615dbc2&searchtype=0

https://www.agefotostock.com/age/en/details-photo/blue-wildebeest-connochaetes-taurinus-suckling-newborn-calf/IBR-3541262

Posted by milewski over 1 year ago

Shift

@paradoxornithidae

Manelessness in Equus quagga boehmi in Amboseli National Park, Kenya:

https://www.flickr.com/photos/jozioau/22706412016/

Posted by milewski over 1 year ago

The case for a bleeze on the rump and back is weak in all forms other than mearnsi. However, the flowing show that, in certain illuminations, this effect can occur in albojubatus:

https://www.inaturalist.org/observations/42931933

https://www.inaturalist.org/observations/56587653

https://www.inaturalist.org/observations/56439577

Posted by milewski over 1 year ago
Posted by milewski over 1 year ago

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