The peculiar caudal flag of the western dama gazelle

The western dama gazelle (Nanger dama mhorr) has such striking colouration that it is easy to overlook how peculiar the tail is relative to other gazelles.

All species of Gazella, Eudorcas and Ammodorcas have a tail that is large, dark and mobile enough to constitute a caudal flag, particularly in juveniles. The tail is wagged and/or raised in various situations, postures and gaits. For example, the erect tail of the goitred gazelle (Gazella subgutturosa) is so obvious when the animal flees that an alternative name for the species is 'black-tailed gazelle'. In Thomson's gazelle (Eudorcas thomsoni) the tail is wagged nervously as the alert or initially alarmed animal walks slowly and indecisively about in the face of possible danger (see https://www.shutterstock.com/ja/video/clip-21099121-thomson's-gazelles-walking-maasai-mara-kenya-africa and https://dissolve.com/video/Thomson-Gazelles-Grazing-Long-Grass-Maasai-Mara-Kenya-rights-managed-stock-video-footage/002-D806-97-026).

The tail skeleton of the western dama gazelle is about as long, proportional to the body, as in other gazelles, but the tassel - proportionately the smallest of any gazelle - looks negligible. Furthermore, the tail is not demonstrative in adults, being largely inert except when swished to shoo insects. Even when the adult stots to show off its fitness, the tail is kept down. One way to interpret this is that the whole figure is so conspicuously emblazened, with the rump and buttocks in particular so conspicuously white, that accentuation by the tail is superfluous in this subspecies.

The tail of the infant of the western dama gazelle is small relative to those of the infants of other gazelles, owing to the extreme diminution of the tassel. However, it does constitute a caudal flag (see https://www.alamy.com/gazelle-in-blijdorp-rotterdam-the-netherlands-image240604149.html). At birth, the tail is pale fawn at the base and tip, but covered in white erectile hairs along the middle of the stalk. The tail is raised and wagged demonstratively when the infant stots playfully, as well as while it suckles. Until the horn-tips emerge, the infant has a thoroughly cryptic and camouflaged pattern of colouration except for the raised or moving tail.

What is peculiar about the western dama gazelle is not that the tail is most conspicuous in infancy and when waved. Instead it is that this conspicuousness is achieved by means of only a limited tract of fur, which is brought to some contrast with the dullness of the rest of the figure by means of piloerection. The result is that, in this subspecies, the tail is converted from the most noticeable part of the infantile figure to one of the least noticeable parts of the adult figure (see https://www.alamy.com/gazelle-in-blijdorp-rotterdam-the-netherlands-image240604268.html) - with minimal anatomical change as the animal grows. More than in any other antilopin bovid, the western dama gazelle simply outgrows its tail.

Posted by milewski milewski, June 08, 2021 03:51

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