Describing the adaptive colouration of Thomson's gazelle

A bleeze is a bold pattern of animal colouration conspicuous to scanning predators even when the figure remains stationary. This is based not on hues but on dark/pale contrasts. A flag is a smaller-scale pattern of dark and/or pale which becomes conspicuous when the body-part in question is moved; this pattern is relevant both to predators and socially (i.e. for intraspecific communication). A semet is a pattern so small-scale and faint that it is insignificant to scanning predators; it is socially relevant but only in motion and only at close quarters.

Thomson's gazelle (Eudorcas thomsoni) is a suitable species to start with, because its colouration shows negligible sexual dimorphism, minimal change from birth to maturity, minimal subspecific variation, and minimal individual variation except on the forehead and rostrum. The species seems to wear graphic, stereotyped insignia except for subtle variation on the front of the face which may perhaps aid individual recognition.

Thomson's gazelle possesses a lateral bleeze (conspicuous in full profile), a posteriolateral bleeze (conspicuous when the figure is facing obliquely away), a caudal flag (when the black tail is wagged, flicked or raised as a signal) and possibly a buccal semet (accentuating the act of chewing, which is significant for social vigilance).

The following illustrate these patterns.

Lateral bleeze in adult males (see https://www.inaturalist.org/observations/84953383 and https://www.inaturalist.org/observations/63674686 and https://www.inaturalist.org/observations/36762055 and https://www.inaturalist.org/observations/34127361), adult females (see https://www.inaturalist.org/observations/80334434), juvenile males (see https://www.inaturalist.org/observations/67642401 and https://www.flickr.com/photos/42964440@N08/41708380164), and infants (see https://www.allposters.com/-sp/Thomsons-Gazelle-with-Baby-Kenya-Posters_i3855010_.htm and https://stock.adobe.com/images/thomson-s-gazelle-mother-and-baby-fawn-calf-eudorcas-thomsonii-looking-into-camera-golden-grass-masai-mara-national-reserve-kenya-east-africa/274949283).

Posteriolateral bleeze in adult males (see https://www.inaturalist.org/observations/67332095), adult females (see https://www.inaturalist.org/observations/56613345 and https://www.inaturalist.org/observations/6181754) and infants (see https://www.masterfile.com/image/en/841-07355071/thomsons-gazelle-gazella-thomsonii-mother-and). There is an erectile aspect to the posteriolateral bleeze by virtue of the flaring of the fur on the buttocks, particularly in infants and while stotting.

Caudal flag (see https://www.naturepl.com/stock-video/thomsons-gazelle-(eudorcas-thomsonii)-running-away-from-cheetah-(acinonyx/search/detail-0_01660521.html and https://dissolve.com/video/Thomson-gazelle-Serengeti-royalty-free-stock-video-footage/001-D699-2-824 and https://dissolve.com/video/Thomson-gazelle-Serengeti-royalty-free-stock-video-footage/001-D699-2-839). The caudal flag is proportionately largest, and most likely to be erect, in infants.

The case for a buccal semet in Thomson's gazelle rests on the malar stripe pointing to the mouth. It is difficult to interpret the malar stripe, which runs diagonally across the side of the face from the eye, as having any other function. See https://www.gettyimages.in/detail/video/thomsons-gazelle-chews-cud-while-lying-in-the-stock-video-footage/3B2FBBC6_0010 and https://www.masterfile.com/image/en/6119-08741136/male-thomsons-gazelle-gazella and https://www.wildscreenexchange.org/stock-photo/thomsons-gazelle-side-view-of-face/search/detail-0_00021634.html.

Posted by milewski milewski, 04 July, 2021 10:24

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Here is the posteriolateral bleeze of the infant of Nanger granti granti (the location is Amboseli) for comparison: https://www.crushpixel.com/stock-photo/young-gazelle-savannah-151651.html.

Posted by milewski over 1 year ago (Flag)

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