Introducing conspicuous patterns about the ears of ungulates

One of the puzzles of adaptive colouration in ungulates is the pale patches which occur at the bases of the ears of certain species, including species with otherwise plain colouration. Among the clearest examples of this are the moose (Alces alces) and the sambar deer (Rusa unicolor). As the ears swivel with changes in attention or emotion, the pale/dark contrasts flick in and out of view, potentially helping onlookers to read the mind, as it were, of the animal in question (e.g. see and and and and and and

Adaptive reasons for distinct patterns of colouration at the base of the ears include: a) group-members are likely to monitor the movements of each other's ears continually, so that when an individual becomes suspicious its companions can easily detect the direction in which it is listening; and b) in those species which use their ears for facial expressions, the posture of the ears can be emphasised by the 'makeup' of the colouration.

Ungulates may pay attention to each other's ears much as we humans pay attention to each other's eyes. The direction of gaze, and the pattern of movement of the eyes, imply where someone is directing his/her attention; we are extremely perceptive of the whites of the eyes because these accentuate even slight movements of the eyeball (see 'cooperative eye hypothesis' in Wikipedia). Ungulates lack a retinal fovea, and their visual system emphasises the scanning of a wide visual field for movement, rather than focussing on any particular object. This, together with the separation of the eyes on the sides of the head, means that ungulates would learn little from observing each other's eyes even if the whites showed. Instead, it makes sense to monitor the movements of the ears, which would make the pale/dark patterns on or at the base of the ears analogous to human eye-whites.

Please see and and and and for views of the pattern of pale and dark on the ears of the moose, a species which otherwise lacks clearly-defined markings. In the case of the sambar deer, the pale markings at the anterior and posterior bases of the ears are shown in, and and are also illustrative.

In my last Post I introduced the concept and name of the buccal semet. In the case of the ears we once again have a semet, i.e. a definite pattern with potential for communication, but one too small-scale to matter for the overall conspicuousness/inconspicuousness of the animal to scanning predators. In this case, I propose the term 'auricular semet'.

Posted on May 13, 2021 07:26 AM by milewski milewski


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