Adaptive colouration in wildebeests, part 9: individual variation
The main aspects of colouration subject to individual variation in wildebeests are the brindling and the pattern on the forehead in juveniles and females. Individual variation is less in gnou than in the other forms.
In their variation on the front of the face, wildebeests (other than gnou) are similar to coexisting migratory species such as Eudorcas thomsoni and Taurotragus oryx. However, the face tends to be the most individually variable part of the figure even in sedentary species. For example, the impala (Aepyceros melampus) shows negligible variation in colouration on a sexual, ontogenetic or individual basis, but retains noticeable variation on the face. This is presumably because the main function of facial variation is individual recognition.
The front of the face of wildebeests varies particularly in the paleness of the forehead relative to the rostrum. This differentiation starts in infancy and sharpens in juveniles, taking the shape of a V between the eyes (see https://www.rhinorest.com/wildebeest-facts/ and https://unsplash.com/photos/H9CUOsPXBjw). The pattern tends to disappear with age (see https://backpackers-review.com/trip-reports/south-africa-safari-greater-kruger/#jp-carousel-10355), particularly in males. The V-shape tends to link the straight horns of juveniles, making for a larger V or U which - coincidentally like the 'peace' hand-sign - may appease adult males.
Mature males are the most uniform in their darkness on the front of the face (e.g. see https://www.alamy.com/stock-photo-group-of-wildebeests-animal-life-in-africa-mammals-79464841.html), but even they retain some variation.
Another feature is a horizontal, relatively pale bar, across the rostrum, which consists of relatively long fur and appears faintly already in infants (see https://www.alamy.com/stock-photo-wildebeest-calf-15486243.html). In most forms of wildebeest this is rare and a mere trace (https://www.alamy.com/stock-photo-a-lone-wildebeest-gnu-face-to-camera-feeds-in-the-long-autumn-grasses-138963853.html).
It would hardly have been noticed were it not vividly expressed in some mature individuals, particularly males, of johnstoni (see http://www.africahunting.com/hunting-pictures-videos/showphoto.php?photo=10621&title=nyasaland-gnu-in-tanzania&cat=506 and https://www.africahunting.com/threads/hunting-the-3-wildebeest.5630/). And even within johnstoni it is well-known partly because commercial hunting in Tanzania promotes the selection of those individual males bearing a conspicuous insignia which adds value to the trophy.
The variations in mearnsi are so complex that it can appear that every individual in a group is unique (see https://www.alamy.com/stock-photo-blue-wildebeest-brindled-gnu-white-bearded-wildebeest-connochaetes-76116481.html).
The following are further illustrations:
mearnsi:
https://www.shutterstock.com/nb/image-photo/portrait-wildebeest-national-park-kenya-africa-314138060).
http://walkthewilderness.net/wp-content/uploads/2013/09/Wildebeest-0812.jpg
https://www.alamy.com/stock-photo-portrait-of-a-blue-wildebeest-connochaetes-taurinus-58908845.html
https://lbah.com/wp-content/uploads/2013/03/Serengeti2013-Wildebeestfaces1.jpg
https://www.alamy.com/stock-photo-wildebeest-in-masai-mara-82992967.html
taurinus western form:
https://www.alamy.com/an-immature-blue-wildebeest-in-kalahari-savanna-image263280437.html
https://www.alamy.com/stock-photo-blue-wildebeest-south-africa-70086642.html
https://www.alamy.com/a-closeup-view-of-the-head-and-shoulders-of-an-african-wildebeest-connochaetes-gnou-these-are-very-common-antelope-of-the-southern-savannas-image273234830.html
cooksoni and johnstoni:
third and fourth photo respectively http://en.krugervanzyl.co.za/wildebeest/sub-species.html
Comentarios
In gnou there is the occasional individual (including juveniles and adult females) with a whitish patch of variable size on the forehead (e.g. https://southafrica.co.za/ss/black-wildebeest.html)
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