Locomotory and postural peculiarities of the impala

The impala (Aepyceros melampus) has normal proportions for an ungulate, but its body movements are odd compared to antelopes and deer of similar size and shape.

Many types of antelopes and deer stot, but the kick-stotting of the impala is surprisingly different from gazelles or the kob (Kobus kob), which ecologically replaces the impala North of the equator. As it runs, the impala flings both its hind legs high in unison - in some cases so high that it seems to risk somersaulting - while waving its tail high as well. Few naturalists have observed kick-stotting in response to the approach of predators, possibly because this gait is reserved for the African hunting dog (Lycaon pictus). When charged by most types of predator, the impala neither stots nor raises its tail as it flees, which means that by far the most instances of kick-stotting photographed so far have been in social play, which is rehearsal rather than the real, life -or-death purpose of this gait.

The impala is surprisingly reluctant to trot, which is a normal gait taken for granted in most unguligrade and digitigrade mammals, and in some of them exaggerated into a form of stotting called 'style-trotting'. I have noticed that one of the few times when the impala trots is in slowing down to a halt after a bout of kick-stotting.

The impala is one of the few species of bovids or deer that is inept at swimming. This was first noticed during the rescue operations of wildlife stranded on islands in the rising waters of Kariba Dam. It seems odd that even desert gazelles, which spend their whole lives without encountering a river, can swim more competently than the impala, which often lives along river banks where it must risk being chased into the water by predators.

The impala is capable of standing and even (in the case if the courting male) walking bipedally. However, it seems unwilling to rise on its hind legs to forage, even in drought when the only remaining food is high on branches.

The impala is renowned for its bounding. However, this gait is not as distinctive as it may seem, for the ecological counterpart in India. the blackbuck (Antilope cervicapra), is similarly accomplished in bounding high and far.

Finally: even in the case of lying down to chew the cud, the impala seems odd. Whereas most other antelopes and deer - and even giraffes - are easy enough to spot lying down by day, the adult impala tends to remain standing during its midday rest, reserving its recumbency for the secrecy of night, which it tends to spend in certain open places away from vegetation. Perhaps this explains why photographers so seldom capture the impala in a lying position?

Posted by milewski milewski, April 12, 2021 14:03

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Adding to the point about the impala being reluctant to stand upright: the blackbuck (Antilope cervicapra) specialises more on herbaceous plants and is thus less likely than the impala to seek the foliage of shrubs for food. Yet females of the blackbuck sometimes rear up on their hind legs to chop at each other with their hooves, which as far as I know has never been observed in the impala.

Posted by milewski 18 days ago (Flag)
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The well-grown young (juvenile rather than infant) ruminant needs either to kneel or to splay its fore legs if it is to continue to take milk from the mother. In the impala the posture adopted by the juvenile at the udder is splaying, not kneeling. This is not in itself remarkable, because various bovids and cervids do the same. However, it has been postulated that the impala is most closely related to alcelaphins, which (together with hippotragins and several other antelopes such as the nilghai) instead adopt the kneeling posture during suckling. Also, one can find on the Web photos of the kob (Kobus kob) mislabelled as the impala, and a giveaway is that the juvenile is kneeling, not splaying, under the mother.

Posted by milewski 16 days ago (Flag)

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