Adaptive colouration in wildebeests, part 1: an introduction to large-scale, conspicuous features

Most species of ungulates have certain inconspicuous features and certain conspicuous features of colouration, depending on the range/scale.

Wildebeests (Connochaetes, https://www.inaturalist.org/observations?place_id=any&taxon_id=42279&view=species) are relatively large-bodied, extremely gregarious, and typically found in open vegetation. This leads to the questions:

  • what is the overall effect at a distance, and
  • how does this differ among the various species and subspecies?

All forms of wildebeests have some degree of brindling (https://en.wikipedia.org/wiki/Brindle), which in principle serves to detract from conspicuousness (https://www.inaturalist.org/observations/120472829). However, this is usually outweighed by features of colouration that are adaptively conspicuous to scanning predators by day.

For example, mearnsi (https://www.inaturalist.org/observations?taxon_id=425038) advertises itself rather than trying to blend into the background (https://www.tanzaniaodyssey.com/blog/wp-content/uploads/2019/04/Tz7.jpg and https://www.dreamstime.com/lion-hunting-wildebeest-background-lioness-kenya-africa-hunting-wildebeest-background-migration-season-image102593663).

What is particularly noteworthy about this genus is the diverse ways in which the dark/pale contrasts have been achieved.

So, let us examine adults of the various species/subspecies (https://www.researchgate.net/figure/Map-showing-the-distribution-of-wildebeest-subspecies-in-Africa-including-some-important_fig2_305317918).

In gnou (https://www.inaturalist.org/taxa/42281-Connochaetes-gnou), conspicuous overall darkness (https://www.inaturalist.org/observations/124074386 and https://videohive.net/item/black-wildebeest-herd-in-grassland/28616219 and https://www.alamy.com/black-wildebeest-standing-in-grass-in-profile-image402457280.html) is achieved mainly by a poorly-understood anti-sheen quality of the pelage. This is based on the physical structure of the hairs as much as their pigmentation.

In other forms of wildebeest, this anti-sheen effect is less extreme, and is combined with a sheen effect on the rump (broadly-defined).

This combination of anti-sheen and sheen is most easily illustrated in mearnsi. The figure combines overall darkness with a pale-looking rump (https://www.inaturalist.org/observations/142137050).

The impression of pale on the rump is produced by sheen rather than depigmentation (https://www.inaturalist.org/observations/77947564 and https://www.inaturalist.org/observations/41187666 and https://www.inaturalist.org/observations/36223318 and https://www.inaturalist.org/observations/139835345 and scroll in https://www.tripspoint.com/1/kenya/nairobi/tour/multi-day-tours-cruises/masai-mara-wildebeest-migration-safari/846 and https://www.inaturalist.org/observations/69048380 and https://www.inaturalist.org/observations/126453057).

In albojubatus (https://www.inaturalist.org/observations?taxon_id=525438), the beard and cheeks are conspicuously pale relative to the dark front of the face (https://safaritalk.s3.amazonaws.com/monthly_04_2015/post-49296-0-93207700-1428854993.jpg and https://endangeredandrareanimals.net/2020/01/09/white-tailed_wildebeest/ and https://www.dreamstime.com/eastern-white-bearded-wildebeest-backlit-grazing-amboseli-national-park-kajiado-county-kenya-connochaetes-taurinus-albojubatus-image194773653).

In taurinus, the figure tends to look dark, with some degree of paleness owing to sheen on the rump. However, this is possibly the form with the least conspicuous colouration, overall (https://www.inaturalist.org/observations/82891645 and https://vagabundler.com/south-africa/wildlife-wildebeest/ and https://www.istockphoto.com/photo/blue-wildebeest-in-kruger-national-park-gm1341933056-421513940?phrase=blue%20wildebeest%20bull and https://www.inaturalist.org/observations/144497260).

In mattosi (https://www.inaturalist.org/journal/milewski/67992-photo-pair-summarising-the-distinction-between-blue-wildebeest-and-western-wildebeest), the dark mane is permanently erect. This, in combination with the dark beard and front of the face, gives the anterior of the figure in profile a conspicuously dark emphasis (https://www.picfair.com/pics/011975278-wildebeest-antelope and https://www.inaturalist.org/observations/140473576).

In johnstoni (https://www.inaturalist.org/observations?taxon_id=516812) there is, in some individuals, a bold whitish (depigmented) bar on a dark-pigmented face (https://fineart.ha.com/itm/zoology/taxidermy/nyasaland-wildebeest-shoulder-mount/a/5000-48128.s and https://www.africahunting.com/media/32-nyasaland-wildebeest-tanzania.3371/).

In cooksoni (https://www.inaturalist.org/observations?taxon_id=504448), the front of the face is conspicuously dark relative to the pale forequarters (e.g. see fourth photo in https://www.edwardselfephotosafaris.com/the-top-5-wildlife-attractions).

Returning to gnou:

Both the mane and the tail can be conspicuously pale, by way of depigmentation.

The overall result is as follows:

To be continued in https://www.inaturalist.org/posts/54102-adaptive-colouration-in-wildebeests-part-2-facial-caudal-and-pedal-flags#...

Posted on July 09, 2021 12:09 AM by milewski milewski

Comments

The following shows that the tail of Connochaetes gnou can be truly white:
https://www.zoochat.com/community/media/black-wildebeest-marwell-wildlife.81010/. However, this may be somewhat unnatural, given that these horns are also unusually pale.

Posted by milewski about 3 years ago

The following shows that juveniles of Connochaetes gnou develop the paleness of the tail before the infantile paleness of the feet has been lost: https://www.inaturalist.org/observations/11205548.

Posted by milewski over 1 year ago

In albojubatus, the sheeny paleness on the rump is present (https://www.inaturalist.org/observations/110098228). However, it is not particularly noticeable. This is because a) the ground colour is relatively pale overall (https://www.inaturalist.org/observations/143985891 and https://www.dreamstime.com/herd-wildebeest-eating-grass-wet-plains-amboseli-national-park-kenya-herd-wildebeest-grazing-amboseli-image198106840), and b) the hindquarters are broadly medium-tone greyish (https://www.inaturalist.org/observations/106979241).

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

The following is labelled as mearnsi. However, I suspect that it is actually albojubatus, perhaps in Tarangire National Park:
https://www.dreamstime.com/stock-photo-one-wildebeest-closeup-sideview-standing-ngorongoro-crater-single-head-up-tanzania-image82022937

@capracornelius @tandala @zarek
What would be your identification?

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

In taurinus, all conspicuous features, other than the darkness of the front of the face and of the tail, are weakly expressed. However, this form can be dark enough, overall, to be conspicuous at a distance in open vegetation.

http://www.joelinnphoto.com/africa/xmrwckt8ri8yocv7kwy1dl7ny0ynu1

http://www.wildlife-pictures-online.com/wildebeest_knp-0296.html

Posted by milewski over 1 year ago

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