Is the fibular flag of the moose unique?

The moose (Alces alces) possesses a surprising pattern of colouration. The hindlegs sometimes look strikingly pale (see https://www.gettyimages.com.au/detail/news-photo/november-2020-saxony-moritzburg-bull-moose-between-trees-in-news-photo/1229585955?adppopup=true and https://www.gettyimages.com.au/detail/news-photo/an-elk-is-seen-in-the-forest-near-the-village-of-akhanyany-news-photo/1209275733?adppopup=true). The conspicuous pattern results partly from depigmentation and partly from sheen.

This paleness can extend to the lower legs and the posterior surface of the carpal joint on the foreleg (see https://www.dreamstime.com/mammal-bull-moose-alces-moose-walking-forest-scenery-image134614303 and https://www.gettyimages.com.au/detail/photo/moose-in-the-winter-in-yellowstone-national-park-royalty-free-image/1216705646?adppopup=true and https://www.gettyimages.com.au/detail/news-photo/wild-moose-is-seen-in-the-chic-choc-mountains-in-the-region-news-photo/1129258011?adppopup=true). However, it is most likely to catch the light on the posterior surface of the upper hindlegs, and it is most likely to be noticed when the animal is moving. I therefore propose the name 'fibular flag'.

It is well-known that various species of large ungulates have bold patches on their hindquarters, and it is easy to see that the extreme reduction of the tail of the moose makes it unsuitable as a flag. However, what has not been explained is why the pale feature of the moose is not located on its rump. Why is it only this, the largest of all deer, that possesses a fibular flag?

As we examine the available photos in search of an answer, let us separate Europe from North America because the fibular flag tends to be better-developed in the former then in the latter.

The following shows that the fibular flag is absent in infants: https://www.gettyimages.com.au/detail/photo/sweden-dalarna-juvenile-elk-in-forest-royalty-free-image/548004897?adppopup=true.

The following show the fibular flag in Europe:

https://www.gettyimages.com.au/detail/news-photo/november-2020-saxony-moritzburg-last-week-thursday-the-500-news-photo/1229586037?adppopup=true
https://www.shutterstock.com/nb/image-photo/moose-eating-children-hands-behind-wooden-1332216659
https://www.gettyimages.no/detail/photo/young-bull-moose-in-winter-royalty-free-image/172694357
https://www.dreamstime.com/stock-photo-moose-elk-alces-alces-bull-lying-down-resting-young-antlers-ground-park-norway-image94336209
https://www.shutterstock.com/nb/image-photo/moose-winter-126086303
https://www.dreamstime.com/young-elk-moose-got-separated-his-mother-people-image108373706
https://www.alamy.com/stock-photo-moose-83372960.html
https://www.gettyimages.com.au/detail/news-photo/moose-cow-foraging-on-the-taiga-in-autumn-scandinavia-news-photo/898360256?adppopup=true
https://www.alamy.com/moose-from-behind-image278426197.html

The following show the fibular flag in North America:

https://www.gettyimages.com.au/detail/photo/moose-crossing-road-royalty-free-image/534967298?adppopup=true
http://www.bestofthetetons.com/wp-content/uploads/2013/09/MooseCusterStanding2_Aug27.jpg
https://www.gettyimages.com.au/detail/photo/moose-eating-foliage-in-alaska-royalty-free-image/1289665114?adppopup=true
https://www.alamy.com/bull-moose-alces-alces-in-the-autumn-chugach-state-park-south-central-alaska-alaska-united-states-of-america-image245330006.html
https://www.alamy.com/stock-photo-bull-moose-standing-on-road-in-forest-antlers-adorned-with-grass-after-47231016.html
https://focusedcollection.com/165693352/stock-photo-bull-moose-standing-on-ground.html
https://www.agefotostock.com/age/en/details-photo/rear-end-view-of-a-young-bull-moose-on-its-knees-grazing-in-early-spring-jasper-national-park-alberta-canada/ALK-102OT-JA0001D001-H
https://www.dreamstime.com/stock-photo-moose-back-view-young-image49920788
https://natureexposure.com/gallery/moose/bull-moose-looking-back-moo-0013/#/gallery/moose/bull-moose-looking-back-moo-0013/

The above photos suggest that the fibular flag is similar in female and male, but is clearest in autumn. Other photos, not presented here, show that the plain-coloured summer coat of the moose tends to blend into the surroundings.

In animal colouration, it is in the nature of flags that they can advertise, in certain situations, a figure that has otherwise inconspicuous colouration. This is achieved, in various species of deer, by raising a large tail, or flaring white fur on the buttocks.

A special problem for the moose is that it risks standing out from cover merely because its extremely long legs make it so tall (see https://www.inaturalist.org/observations/90188457). Placing its flag only halfway up the figure means that the paleness remains inconspicuous (owing to shading and/or obstruction by plants) to scanning predators until the animal starts moving, particularly where it breaks cover and enters the sunlight.

With a new search-image, for 'half-mast' flags, we can re-examine other relatively tall deer, which overlap in habitat to some extent with the moose (e.g. see https://www.gettyimages.com.au/detail/photo/idaho-sun-valley-herd-of-wild-animals-in-meadow-royalty-free-image/1278769498?adppopup=true and https://www.dreamstime.com/bull-elk-look-female-moose-brown-field-grand-teton-national-park-image226766868).

The red deer (Cervus elaphus) of Europe has a relatively conspicuous pattern on its hindquarters, but notice that the only real dark/pale contrast is on the ventral part of the buttocks: https://www.gettyimages.com.au/detail/photo/red-deer-stag-in-a-forest-royalty-free-image/1295584462?adppopup=true. This is true also for the wapiti (Cervus canadensis) of North America: https://www.alamy.com/stock-photo-a-bull-elk-looking-back-while-he-forages-along-a-snow-covered-ridge-47277645.html. In both species there is a patch on the rump, well above the level of the tail, but this is nominal rather than functional, because it has become pale brown, not whitish.

I would not describe the bold patterns on the hindquarters of either the red deer or the wapiti as fibular flags, because the dark/pale contrast remains at least as much on the buttocks as on the posterior surfaces of the upper hindlegs. However, they suggest that the difference in colouration shown by the moose is not as categorical as it may seem.

The moose certainly is distinctive. However, what really sets it apart is its its extreme lankiness, which in turn helps to explain the fibular flag.

הועלה ב-אוגוסט 30, 2021 03:33 לפנה"צ על ידי milewski