Colouration of antlers and horns in ruminants, part 1

Antlers, borne by deer (see https://www.wildlifeonline.me.uk/questions/answer/what-are-antlers-and-why-do-deer-have-them), and horns, borne by bovids, are made of bone and keratin respectively. These materials tend to be medium in tone, neither noticeably dark nor noticeably pale. As a result, in most ruminants the conspicuousness of the outgrowths depends on their size and shape rather than their colouration.

However, three exceptions spring immediately to mind in which antlers or horns have conspicuously pale surfaces. The resulting displays seem to have different functions: intraspecific (social/sexual) advertisement in deer and a warning to predators in a bovid.

The antlers of the moose (Alces alces) are not only unusually palmate but also unusually pale. This makes them more showy as adornments. The bleaching is not owing to weathering because it appears as soon as the velvet is rubbed off.
See
https://www.dreamstime.com/stock-photo-moose-denali-beautiful-scenery-alaska-image66051145
https://www.alamy.com/bull-moose-alaska-moose-alaskan-moose-giant-moose-image335113694.html
https://www.dreamstime.com/moose-bull-autumn-landscape-alaska-beautiful-moose-bull-autumn-landscape-national-park-denali-alaska-wilderness-image142535425
https://www.dreamstime.com/beautiful-moose-bull-autumn-landscape-national-park-denali-alaska-wilderness-north-america-wild-animals-nature-image142535154
https://www.dreamstime.com/beautiful-moose-bull-autumn-landscape-national-park-denali-alaska-wilderness-north-america-wild-animals-nature-image142534842
https://www.dreamstime.com/stock-photo-bull-moose-alces-alces-autumn-image83158246
https://www.dreamstime.com/two-bull-moose-feeding-together-denali-national-park-two-male-antlered-moose-together-alaska-image124377745
https://www.hunter-ed.com/montana/studyGuide/Wildlife-Identification-Moose-Elk-and-Pronghorn/20202703_141128/
http://www.maryanningsrevenge.com/2014/02/14-days-of-genitals-day-1-moose-mark-of.html

Comparison with the fallow deer (Dama dama) suggests that the effect in the moose is adaptive and not merely a result of the boniness of antlers. This is because here we have adornments which are palmate without being pale: https://www.dreamstime.com/fallow-deer-stag-dama-autumn-sunset-male-big-antlers-rutting-season-sunlight-nature-colors-clearly-visible-image135982200 and https://www.dreamstime.com/fallow-deer-mating-season-male-there-biggest-beautiful-antlers-image101944500 and https://www.alamy.com/shed-antler-from-fallow-deer-dama-dama-hesse-germany-europe-image151856686.html and https://www.dreamstime.com/stock-photo-fallow-deer-patrol-image22028800 and https://www.dreamstime.com/fallow-deer-dama-dama-winter-landscape-fallow-deer-winter-landscape-image213187835.

The antlers of several genera of deer have conspicuously pale points, again functioning probably only intraspecifically. Deer tend not to defend themselves from predators by means of their antlers, and even during masculine conflict the method is mutual pushing rather than impaling (e.g. see https://www.youtube.com/watch?v=94j5POIloYk). Therefore the accentuation is probably for adornment rather than for warning.

The wapiti (Cervus canadensis) is a prime example: https://www.offset.com/photos/bull-elk-wapiti-banff-national-park-unesco-world-heritage-site-1073158 and https://www.wallpaperflare.com/canada-nature-animals-deer-wapiti-alberta-jasper-antler-wallpaper-wyxnu. However, even the fallow deer: has conspicuously pale brow-tines: https://www.dreamstime.com/beautiful-shot-lonely-elk-long-horns-forest-blurred-background-image162671066.

Among bovids, the most extreme case of conspicuous colouration of horns is the muskox (Ovibos moschatus). However, this conforms less to social advertisement and more to warning colouration directed at non-human predators, today reduced to the wolf (Canis lupus).

Odd-looking horns grow in both sexes of the muskox. The horn-shaft is gleamingly pale, becoming dark only at the sharp tip itself. Adult males additionally have a broad boss at the base of each horn, which is pale against the background of dark fur and oddly free of fur in this otherwise shaggy species. Although females lack bosses, they mimic them by means of a gleamingly pale patch of fur in the corresponding position on the forehead, a pattern that is all the more significant given the remarkably inconspicuous colouration of the ears. Furthermore, this pale patch is precocial, appearing in juveniles long before the horns become noticeable.

Males of the muskox fight with their horns, not by hooking but instead by charging and mutually butting with the blunt bosses (see https://www.youtube.com/watch?v=gKHUZ1K3JHY). For this reason, it cannot be ruled out that the conspicuous pale of the bosses functions intraspecifically. However, what is more likely is that the entire show - of bosses, hooks, and boss-mimicking fur - constitutes a collective display to predators, and the only example of aposematic colouration in any ungulate.

The horn-shaft of the muskox is shaped more suitably for defence than in other ruminants, in its hooked orientation forwards and outwards. However, it is too narrow, particularly in females, to be sufficiently conspicuous in its own right. Hence, I would argue, the bosses are incorporated into the display, and the display of the bosses is in turn made partly deceptive for aggregate effect.

The muskox forms tight ranks when threatened (see https://en.wikipedia.org/wiki/Muskox), a defensive specialisation unmatched in any other ungulate. This provides an opportunity for a collective show to which even the unarmed juveniles can contribute, and which reminds would-be predators unfamiliar with the muskox that the horn-tips, although small relative to the shaggy bulk of the animals, are lethal.

See
https://www.gettyimages.com.au/detail/photo/musk-ox-yukon-wildlife-preserve-yt-royalty-free-image/157281945?adppopup=true
https://www.gettyimages.com.au/detail/photo/captive-at-the-alaska-wildlife-conservation-center-royalty-free-image/560119055?adppopup=true
https://www.gettyimages.com.au/detail/photo/close-up-of-a-muskoxs-head-ovibos-moschatus-royalty-free-image/699102849?adppopup=true
https://www.gettyimages.com.au/detail/news-photo/muskox-close-up-portrait-on-the-tundra-in-autumn-dovrefjell-news-photo/809839890?adppopup=true
https://www.gettyimages.com.au/detail/news-photo/muskox-close-up-portrait-on-the-tundra-in-autumn-dovrefjell-news-photo/809839882?adppopup=true
https://www.gettyimages.com.au/detail/photo/musk-ox-north-slope-alaska-usa-close-up-royalty-free-image/70010156?adppopup=true
https://www.gettyimages.com.au/detail/photo/the-musk-ox-royalty-free-image/1000167850?adppopup=true
https://www.gettyimages.com.au/detail/photo/muskox-royalty-free-image/98059251?adppopup=true

Posted on September 01, 2021 10:14 AM by milewski milewski

Comments

wonderful report on cervid antlers.

Posted by natureali almost 3 years ago

@natureali Many thanks for your kind words of encouragement.

Posted by milewski almost 3 years ago

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