Introducing and naming cud-chewing displays

Many ungulates deal with predation partly by being gregarious. Even 'solitary' species may rest in sight of a mate or parent when ruminating, i.e. chewing the cud. A 'strength in numbers' is that the group - whether it numbers two or twenty - functions as a unit in cooperative vigilance by virtue of its collective eyes, ears and noses. The moment one individual becomes suspicious and stops chewing to listen up, the apprehension needs to be communicated efficiently across the 'white noise' of the tooth-grinding of group-members.

The point of mutual monitoring of the routine chewing of companions would be to detect any interruption immediately, and to direct attention accordingly.

Ruminants have a problem which humans do not: they spend much of their lives, both night and day, noisily grinding the cud - while at the same time maintaining constant vigilance by hearing (e.g. see https://www.youtube.com/watch?v=E_Uc0kfNvgg).

The visual system of ungulates is extremely sensitive to slight movements. However, it makes adaptive sense that various species would have evolved patterns of colouration around the mouth to accentuate, or 'amplify', the chewing motion, particularly when the light is dim. And that each species would produce its own 'signature' pattern (e.g. see https://www.shutterstock.com/nb/image-photo/cud-chewing-deer-584459 and https://www.shutterstock.com/nb/image-photo/elk-chewing-his-cud-grasslands-82571272 and https://www.shutterstock.com/nb/image-photo/close-young-bull-elk-537907132 and https://www.inaturalist.org/observations/47408137).

Is it possible that, once the naturalist has a search-image along these lines, the diverse patterns of dark and pale on the lips, chin, cheeks and muzzle of various ruminants may start to look less like random scribblings of capricious Nature and more like functional adaptation?

Here are two examples to start with, illustrating the greater kudu (Tragelaphus strepsiceros, see https://www.storyblocks.com/video/stock/a-female-kudu-chews-cud-in-kruger-national-park-south-africa-e_zttsjf2eillivjey) and common eland (Taurotragus oryx, see https://depositphotos.com/58556159/stock-video-common-eland-head.html and https://www.alamy.com/elenantilope-taurotragus-oryx-nrnberg-bayern-deutschland-image69178906.html).

Note the puzzlingly intricate patterns on the faces. The dark muzzle contrasts with the pale mouth and chin, and there are dark or pale markings on the side of the mandible. Why would such patterns have arisen?

In my last Journal Post I proposed the new term 'semet' for patterns of this small scale, functioning at the close range of social communication but not mattering much to the large-scale conspicuousness or inconspicuousness of the figure to scanning predators. Because this particular category of semet concerns movements of the mouth, I propose calling it a 'buccal semet'. We can expect the buccal semets of the greater kudu and common eland to be dark/pale patterns unique to these species.

Of course the idea is still just hypothetical that ruminants are adapted to spot interruptions in the rumination of companions. And any new technical term may sound awkward at first. But could this open a new line of investigation into the subtle messages hidden in our photos of ungulates?

Posted by milewski milewski, May 12, 2021 11:57

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The buccal semet of the grey rhebok (Pelea capreolus) can be seen in the well-illuminated photo at https://www.inaturalist.org/observations/16496842.

Posted by milewski over 1 year ago (Flag)

The buccal semet of the impala (Aepyceros melampus) can be seen in https://www.safaritalk.net/topic/14291-tsavo-west-amboseli-meru-samburu-%E2%80%94-january-2015/page/8/.

Posted by milewski over 1 year ago (Flag)

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