Is the colouration of Dorcas gazelle conspicuous or inconspicuous?

The colouration of the Dorcas gazelle is ambivalent. On one hand, it could be that the adaptive function is to hide the animal in plain sight in its environment, which is open because this is a species of the desert. On the other hand, it could be that gazelles, far from trying to hide, advertise themselves for the sake of gregariousness and the display of fitness, which are arguably their best strategy versus predators given their inevitable exposure.

In the past, almost all authors have assumed that the Dorcas gazelle's colouration blends into the desert, following the rationale of camouflage. However, I see the animal differently: Gleaming out like a beacon in most illuminations. In my view, it is not that this gazelle is pale to match the pale sand; instead, it is so pale that it becomes a living highlight. The most important element in its pattern, ensuring conspicuousness, is the extension of the white underparts to a level so high on the flank and rump that, even at noon, the white is likely to draw attention to the figure.

So which of these opposing interpretations is true?

What is not readily apparent from photos is that the Dorcas gazelle continually wags its tail, which is particularly conspicuous in being the only black part of the body. Because the eyes of ungulates and predators alike are extremely sensitive to motion, this continual movement is a real giveaway as to the antipredator strategy of this gazelle. Instead of 'freezing' in alarm and crouching low as camouflaged antelopes would do in dense vegetation, the Dorcas gazelle advertises itself and its fitness, relying on its ability to outrun the predator.

For its part, the predator relies on spotting any individual which is sick, old or injured, as betrayed by any slight failure to stot vigorously, to alarm-sneeze loudly or to keep up the flagging of the tail.

In reality, the colouration of most ungulates is probably some complex combination representing an adaptive compromise between hiding and self-advertisement. For example, the colouration of the large ears of the Dorcas gazelle suggests camouflage of that part of the figure at least. And it is possible that the same overall pattern which gleams by day actually hides the whole body when the light is dim. One way to investigate this would be to see whether gazelles behave differently when alarmed by night, freezing, keeping quiet and facing the threat rather than presenting the bold hindquarters as they typically do by day.

פורסם על-ידי milewski milewski, ספטמבר 08, 2020 12:33 לפנה"צ


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