Gaits and anti-predator displays, compared between deer (Odocoileus) in North America and impalas (Aepyceros) in Africa

There is an adaptive trend among the ruminants of the world, as follows.

Species adapted to dense cover tend to have

  • inconspicuous colouration (particularly on the hindquarters),
  • a halting gait, viz. the semi-crosswalk,
  • a lack of stotting (strenuous displays of individual fitness, dissuasive to scanning predators), and
  • non-gregarious society.

A typical example is bushbucks (Tragelaphus, and

By contrast, species adapted to short, sparse vegetation tend to have

  • conspicuous colouration (particularly on the hindquarters),
  • a smooth gait, viz. the amble,
  • stotting, and
  • gregarious society.

A typical example is the springbok (

Intermediate species show intermediate traits.

In the context of this adaptive axis, certain anomalies emerge. The following are prime examples.

Deer of genus Odocoileus in North and central America, and impalas (Aepyceros) in southern and East Africa, are comparable. Both fall into the intermediate part of the axis described above.

Both are associated with some woody cover, as opposed to treeless grassland. Accordingly, both are somewhat gregarious.

Both have

  • medium body mass (about 50 kg),
  • unremarkable body-proportions, and
  • fairly nondescript colouration on forequarters and torso.

However, two incongruities emerge, as follows.

Firstly, Odocoileus deer combine

  • a halting walking gait, linked to cover-dependence and non-gregariousness, with
  • conspicuous colouration on the hindquarters, linked to open environments and gregariousness.

By contrast, impalas combine

  • a smooth walking gait, linked to open environments and gregariousness, with
  • inconspicuous colouration on the hindquarters, linked to cover-dependence and non-gregariousness.

Secondly, both genera have stotting displays. However, the gaits used are surprisingly different.

Odocoileus deer display by

By contrast, impalas display by

Stating the puzzle concisely:
The deer referred to are incongruently demonstrative, whereas impalas are incongruently non-demonstrative.

Before attempting to explain this puzzle, let us examine the evidence by means of photos/video clips.

The following show the semi crosswalk, which is

  • associated with cover-dependent ruminants, and
  • in the case of Odocoileus has been 'exaggerated' into demonstrative walking.

What is remarkable is that a halting gait, allowing the animal to 'freeze' with two legs in the air in order to blend into the background when hearing or seeing something suspicious, has been converted from an adaptation for concealment to an adaptation for advertisement. This has been done not by changing the footfall-sequence, but by exaggerating the lifting/lowering of the feet into conspicuous movements, probably together with release of odour from the pedal glands.,vid:_9UiYWLW3aw,st:0,vid:r3qAhrvKi5I,st:0,vid:sXdOEAV_2w4,st:0

Posted on February 06, 2024 11:44 PM by milewski milewski


Posted by milewski 6 months ago
Posted by milewski 6 months ago
Posted by milewski 5 months ago

The ventral surface of the tongue is flesh-coloured in Aepyceros melampus, despite the upper surface being dark:

Posted by milewski 5 months ago
Posted by milewski 5 months ago

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