A previously overlooked pattern of colouration in Ovis dalli stonei, the most remote of wild sheep in North America

Here is a pattern of colouration in a bovid ruminant, that may not have been noticed before: https://www.alamy.com/stock-image-female-stone-sheep-northern-british-columbia-canada-162698212.html?imageid=8EC65BA7-BB9D-4A27-BDE2-6DEE60C4C0E2&p=281926&pn=6&searchId=ebb9bca2261153f28e7493b22d14c7bc&searchtype=0 and https://www.inaturalist.org/observations/69485518 and https://www.inaturalist.org/observations/70126258.
 
The animal I focus on is Ovis dalli stonei (https://www.inaturalist.org/observations?page=2&place_id=any&taxon_id=237607), which is coveted by hunters as one of the most prestigious trophies in North America.
 
Anyone familiar with North American game mammals will know of Ovis canadensis. Most will also realise that, in the far north of North America, O. canadensis is replaced by an all-white form of mountain sheep, namely Ovis dalli dalli (https://www.inaturalist.org/observations?taxon_id=237605).

However, few naturalists, other than hunters, will be familiar with O. dalli stonei. This is because this subspecies

• lives in one of the most remote parts of the continent (see map in https://www.slamquest.org/animal-details.php?a=30), and
• tends to befuddle the lay person by being so different from its subspecies O. dalli dalli in colouration.

There are hundreds of photos of O. dalli stonei on the Web, because the ‘pied’ in colouration of this subspecies tends to be photogenic. Hunters appreciate this particular pied mammal, on account of its magnificent horns, and the challenging terrain in which it must be hunted.
 
The following specimens, mounted by taxidermists, show the typical appearance of O. d. stonei: 
https://wildimagesinmotion.com/stone-sheep-1/
http://www.artistic-taxidermy.com/images/lifesize/stone-sheep-6.jpg
https://www.monarchtaxidermyinc.com/janda/newphotos.php?start=90&ID=22&PId=1084&MID=22.

The following, fairly realistic painting (http://www.artbarbarians.com/gallery2/images/26/Stone%20Mountain%20Stone%20Sheep%20by%20Nancy%20Glazier%20Large121223141.jpg) shows the colouration of O. d. stonei. Everyone familiar with this subspecies knows that it is generally grey, with a pale head and posterior, plus a pale belly.
 
Nobody familiar with O. d. stonei can have failed to notice that it advertises its posterior by means of a contrast between the pale on the rump, buttocks, and posterior surfaces of the hind legs, and the dark of the tail. In some specimens the crisply-defined anterior edge of the pale posterior, on the haunches, is accentuated by dark. The result is a category of adaptive colouration that I call a bleeze.

This bovid becomes particularly conspicuous when it turns away from the observer: https://s-media-cache-ak0.pinimg.com/736x/8f/b7/86/8fb786dbe3cf350be6af58af8e4819d7.jpg. This pattern of ‘flight announcement’ is widespread in mammals and birds.
  
The following shows this posterior bleeze to good effect: http://www.oneshotadventures.com/sheeppage2.jpg. This pattern is surely designed to make the animal conspicuous in certain circumstances. Similar patterns occur in many species of ungulates, and most forms of wild sheep.

So what could I possibly have noticed that is new?

Please examine the individual on the right in http://falconhunter.com/images/stones-sheep-rams.jpg. There is a dark marking located between the flank and the upper foreleg, which comes into view as the animal faces obliquely away from the observer. And in this case this dark punctuation is almost as striking as the pale on the rump. Is this just an illusion caused by a shadow?

The following (https://www.inaturalist.org/observations/19544678) is an individual in which an additional whitish patch offsets the dark near the elbow.

The following show mature male specimens taken by hunters, which inadvertently allow us to focus on this mysterious dark marking on the lower anterior flank just behind the elbow:
https://outdoors-international.com/hunting-trips/sheep/stone-sheep/stone-sheep-hunt/ 
https://huntingagent.com/category/hunting-sheep/
http://anchorbaroutfitting.com/images/yukonsheep/ss03.jpg
https://kuiu.tumblr.com/post/59705518263
https://www.youtube.com/watch?v=I8h39eMqmW4
http://gillnockies.com/stones-sheep
https://steveshunts.com/hunting-packages/stone-sheep-hunts
https://www.facebook.com/WildSheepSocietyBC/photos/a.547707895279895/4003638793020104/?type=3.

Although it is easy to assume that the whitish of the belly of O. d. stonei extends all the way to the brisket, this is in fact not so. Instead, the ventral surface of the chest is among the darkest parts of the pelage. However, one may not notice this dark/pale contrast unless the animal is viewed from obliquely behind.
 
See http://voyagerexpeditions.com/images/britishcolumbia/bcstonesheep.jpg.
 
The following (http://kawdyoutfitters.com/uploads/images/Gallery/Stone-Sheep/rams%20tootsee%20074.JPG) shows the contrast between the dark of the anterior lower flank and the white of the elbow.

The following (https://gohunt-assets.s3.amazonaws.com/media/Nathan-French-with-his-giant-Stone-sheep-12.jpg) clearly shows that O. d. stonei is not simply a grey animal with a white ventral surface to the torso. Instead, there is a dark/pale contrast on the surface posterior to the elbow. 

Even in this relatively pale individual, the dark marking remains noticeable: https://s-media-cache-ak0.pinimg.com/236x/7e/3d/c0/7e3dc039d46741ad7d3e8adeb56f7d56.jpg.

The unprepared eye might overlook this pattern, of a dark area posterior to the elbow, as a mere shading effect: http://bcsafaris.com/wp-content/uploads/2011/01/stone-sheep.jpg . But it is a feature in its own right, helping to offset the bleeze on the hindquarters

The following show that this ‘elbow-patch’ occurs even in females and/or juvenile males:
https://www.dreamstime.com/stock-photo-stone-sheep-ewe-lamb-roadside-northern-british-columbia-canada-image61485690
https://www.inaturalist.org/observations/53318666.
 
The following (http://c8.alamy.com/comp/CFD1DH/one-horned-female-stone-sheep-ovis-dalli-stonei-muncho-lake-provincial-CFD1DH.jpg and http://media.gettyimages.com/photos/stone-sheep-lamb-muncho-lake-provincial-park-british-columbia-canada-picture-id145108472?s=170667a) are adult females of O. d. stonei. It is now clear that we cannot dismiss this dark marking behind the elbow as a mere shadow.
 
The following (http://c8.alamy.com/comp/CFD2E4/stone-sheep-ovis-dalli-stonei-on-the-alaska-highway-in-muncho-lake-CFD2E4.jpg) shows the full colouration of adult females of O. d. stonei.

Here again, we can confirm that this ‘elbow-patch’ occurs in females and juveniles, and not just in mature males: http://c8.alamy.com/comp/BRAMK3/stone-sheep-ovis-dalli-stonei-ewe-and-lamb-stone-mountain-provincial-BRAMK3.jpg. There is a ‘flank-band’ effect by virtue of the dark band between the grey flanks and the white belly, and this is similar to that found in many other caprin bovids. However, few other bovids have the abrupt switch from white to near-black on the anterior part of the lower flanks, as seen here.

The following (https://www.inaturalist.org/observations/427394 and https://www.inaturalist.org/observations/10646215 and http://m1.i.pbase.com/g1/84/49084/2/104352591.syULvOsN.jpg) again nicely illustrate the posterior bleeze that everyone already notices in wild sheep.
 
The following painting of O. d. stonei does depict the dark behind the elbow: https://s-media-cache-ak0.pinimg.com/736x/81/37/d1/8137d10e1d8b969d3e569aea977ee75a.jpg. However, note the erroneous depiction of the white ventral surface as tapering towards the anterior – as it indeed does in so many other taxa of ruminants. This artist has been unobservant of the true pattern found in O. d. stonei. Again, compare the painting with this mounted specimen: https://wildimagesinmotion.com/stone-sheep-1/.

Dear reader, with this new familiarity of the colouration in O. d. stonei, please compare the more familiar spp. of wild sheep, namely

• O. canadensis (https://www.dreamstime.com/bighorn-sheep-glacier-national-park-montana-usa-bighorn-sheep-natural-habitat-glacier-national-park-montana-usa-image161509328 and https://en.wikipedia.org/wiki/Bighorn_sheep), and
• O. musimon (https://www.shutterstock.com/image-photo/european-mouflons-snow-131169092 and https://en.wikipedia.org/wiki/European_mouflon).

The colouration of O. canadensis is relatively plain.

However, please note that even the peninsular bighorn sheep (Ovis canadensis cremnobates) - living so far from O. dalli stonei that it occurs in Mexico - can have a discernible dark patch posterior to the elbow: http://images.fineartamerica.com/images-medium-large/endangered-peninsular-bighorn-sheep-ram-rich-reid.jpg.

Posted on August 20, 2022 09:32 AM by milewski