The peculiarly versatile tail of the impala

It has long been realised that the impala (Aepyceros melampus) is something of a 'living fossil', unrelated to antelopes of superficially similar appearance. However, what seems to have been overlooked is the versatility of the tail relative to other bovids.

The impala normally hides its tail, tucking the tassel between the legs more than occurs in other ungulates including gazelles and the blackbuck (Antilope cervicapra). This is consistent with the peculiar striped pattern on the posterior of the haunches (see https://www.naturepl.com/stock-photo-impala-tail-pattern-aepyceros-melampus-kruger-np-south-africa-nature-image01068237.html), which helps to make the whole animal inconspicuous in the sense of disruptive colouration (roughly equivalent to camouflage). Many ungulates have boldly-marked hindquarters, conspicuous from a distance, and many others have plain hindquarters which blend into the surroundings, but the impala is unusual in blending into the surroundings by means of hindquarters marked similarly to the stripes of the tiger (Panthera tigris). The habitual hiding of the white tassel makes sense in this context.

The impala does frequently display its tail in certain behaviours, but in doing so reveals the caudal anatomy to be unlike that in any other ruminant. Firstly, the long white hairs are piloerected either laterally (as in masculine displays in which the tail looks like a white fan, see https://www.alamy.com/stock-photo-impala-buck-with-tail-raised-and-making-sounds-territorial-behavior-48605342.html) or vertically (as when the tail is flicked up synchronously with the kicking of the hind legs in kick-stotting, see https://www.gettyimages.com.au/detail/photo/impala-leaping-royalty-free-image/10190009 and https://www.inaturalist.org/observations/3739299 and https://www.flickr.com/photos/wild_images/50904109398/). Secondly, it is the ventral surface of the tail on which the vertical piloerection occurs - unlike the tails of various antelopes, including gazelles, on which any vertically-arranged tomahawk-like hairs (usually black) are on the dorsal side.

The impala also shows the white tassel when shooing insects and when passing urine or faeces, but in these cases there is no piloerection in either of the orientations described above (e.g. see https://www.wikiwand.com/en/Impala).

Surprisingly, the length of the tassel differs between the two main subspecies of the impala. Many species of ungulates show subspecific variation in various features, but it is rare for the tails to vary much within a given species. In the black-faced impala (Aepyceros melampus petersi) the tail is so large (eg. see https://m.facebook.com/ongavalodge/photos/a.914545575258908/2515148435198606/?type=3 and https://www.canstockphoto.com/black-faced-impala-ram-showing-its-tail-87852614.html) that it seems to possess an additional curve in its shape as seen in kick-stotting. When tucked between the legs, the tail-tip reaches as far as the prepuce, instead of merely the scrotum.

Publicado por milewski milewski, 18 de abril de 2021

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