Adaptive colouration in wildebeests, part 4: brindling

Wildebeests (Connochaetes) are odd for wild ungulates in possessing irregular, individually variable, vertical streaks, this dark fur being more pigmented than the ground-colour and of a different texture. The resulting brindling reflects light less than the ground-colour does, owing to both pigmentation and the structural properties of the hairs. Skin-folds are also involved (e.g. https://wildmoz.com/wp-content/uploads/2015/11/Blue-Wildebeest-Animals-of-the-Kruger-Park.jpg and zoom in on https://www.flickr.com/photos/tick-my_pictures/39670191313).

Compare the following two views of albojubatus: https://www.kimballstock.com/popuppreview.asp?db=a&image=AFW+03+MH0030+01&itemw=4&itemf=0001&itemstep=1&itemx=8 and https://www.canstockphoto.com/wildebeest-19324182.html. There is individual variation, but the difference in the darkness of the brindling seems to be partly or largely owing to the angle of the light.

As a form of striping (see https://www.123rf.com/photo_93605785_blue-wildebeest-in-the-kruger-national-park-south-africa-specie-connochaetes-taurinus-family-of-bovi.html), brindling should aid inconspicuousness. However, any type of disruptive colouration in wildebeests would seem incongruous because they do not hide in vegetation.

Brindling varies among the forms of wildebeest, as follows.

In gnou, brindling is present but usually unnoticed (see http://www.huntingtrophy.com/wp-content/uploads/2015/07/bigstock-Male-black-wildebeest-Connoch-56643716.jpg and https://www.alamy.com/stock-photo-black-wildebeest-connochaetes-gnou-adult-mountain-zebra-national-park-48741062.html).

In the western form of taurinus (see https://www.inaturalist.org/observations/70216447 and https://www.123rf.com/photo_46595093_blue-wildebeest-in-the-etosha-national-park-namibia.html and https://vreugdeguestfarm.com/en/namibian-wildlife-gallery/?_gallery=gg-3-30), brindling is poorly-developed.

In the remaining forms, brindling is well-developed. Individuals vary in johnstoni (see https://www.inaturalist.org/observations/34868591 and https://www.inaturalist.org/taxa/516812-Connochaetes-taurinus-johnstoni and https://www.africahunting.com/threads/hunting-the-3-wildebeest.5630/ and https://www.shutterstock.com/image-photo/blue-wildebeest-selous-game-reserve-tanzania-1040741800). For cooksoni see https://www.alamy.com/cooksons-wildebeest-a-subspecies-of-the-blue-wildebeest-native-to-the-south-luangwa-national-park-zambia-image332014206.html. For mearnsi see https://www.inaturalist.org/observations/52249793 and https://www.inaturalist.org/observations/61193021.

In the eastern form of taurinus, brindling would seem to aid inconspicuousness of the figure at distances relevant to scanning predators, particularly because this form lacks conspicuous dark/pale contrasts at this scale (e.g. see https://steemit.com/animals/@vagabundler/safari-photo-collection-3-wildebeest-south-africa). However, all forms of wildebeest the lack countershading on the belly and have dark on the brisket. Thus even the eastern form of taurinus retains a conspicuously dark ventral silhouette when the sun is above. And indeed the whole figure remains conspicuously dark at distance (see https://www.inaturalist.org/observations/78807527).

This inconsistency, between striping, which tends to break up the figure, and a dark ventral silhouette, which tends to define the figure, poses a puzzle in the adaptive colouration in wildebeests (see part 8).

All wildebeests formed mixed groups with the plains zebra (Equus quagga). Is brindling analogous with the striping of zebras, or perhaps a subtle form of mimicry? Please see my explanation for striping in zebras (https://search.informit.org/doi/abs/10.3316/ielapa.338162553400534), based on a shimmering effect in predatory eyes, retarding assessment of the individual body-condition in the prospective prey.

Look at a few photos of zebras with small, relaxed eye-movements. You may notice a disconcerting shimmering. Now try the same for 'brindled gnus'. I see less of this effect, possibly because the brindling is not crisp and regular enough to confuse the optical system.

The bottom line for now: the brindling of wildebeests remains one of the more puzzling features of adaptive colouration in ungulates.

Posted by milewski milewski, 09 July, 2021 19:33

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