Caleonic colouration in the caribou, part 1: Rangifer tarandus terranovae
Naturalists are used to thinking that animals tend to have adaptive colouration that blends into the surroundings.
However, in open environments where it is hard to hide, certain animals opt instead to have conspicuous colouration.
One well-recognised pattern of conspicuous colouration in medium-size to large animals is the pied pattern (https://www.tripadvisor.com/LocationPhotoDirectLink-g469397-d469470-i381557535-Bontebok_National_Park-Swellendam_Overberg_District_Western_Cape.html and https://www.flickr.com/photos/myplanetexperience/50867088327).
This consists of a dark/pale patchwork, too bold to function disruptively. I.e. pied colouration is too conspicuous for the figure to be camouflaged.
However, there is another conspicuous pattern, less familiar but obvious in certain mammals. I provisionally call this 'caleonic', because it deserves a name, but has not previously been described.
In the caleonic pattern, it is as if the figure is 'highlit' by a flame below.
Caleonic colouration seems to have arisen repeatedly in lineages as diverse as
- bovids (https://www.alamy.com/male-critically-endangered-dama-gazelle-nanger-dama-northern-africa-image364952487.html and https://mammiferesafricains.org/2022/02/oryx-algazelle/),
- antilocaprids (https://www.inaturalist.org/observations/122793376 and https://www.inaturalist.org/observations/122107163 and https://www.inaturalist.org/observations/120998764 and https://www.inaturalist.org/observations/119233203),
- camelids (https://theconversation.com/when-rewilding-isnt-mad-guanacos-can-transform-the-espinal-of-chile-24248),
- equids (https://www.sciencephoto.com/media/1249170/view/two-male-indian-wild-asses and https://www.sandysharkey.com/blog/2018/10/21/saving-przewalskis-horse), and
- canids (https://www.agefotostock.com/age/en/details-photo/arctic-fox-alopex-lagopus-adult-female-summer-coat-playing-with-cub-nunavut-canada-july/FHR-10406-00211-849 and https://www.alamy.com/stock-photo-arctic-fox-alopex-lagopus-adult-female-summer-coat-standing-on-tundra-52965457.html).
Animals with caleonic colouration have, in a sense, ‘stretched’ the principle of countershading (https://en.wikipedia.org/wiki/Countershading) to breaking-point. This extension of pale pelage, upwards, has achieved whole-body conspicuousness instead of crypsis (https://en.wikipedia.org/wiki/Crypsis).
Caleonic colouration thus differs from pied colouration in how countershading has been modified. In the latter, pale ventral surfaces have been converted into parts of the large-scale, dark/pale contrast in the pigmentation of the pelage.
It is normal for the ventral parts of the body to be pale, as part of the inconspicuous pattern called cryptic colouration. However, the extension of this pale switches the effect to conspicuousness. This is because the pale, encroaching upwards towards the dorsal side, tends to catch the sunlight at
- all seasons, and
- most times of day.
In caleonic colouration, this ‘lateralisation’ of the pale parts of the pelage occurs variously on the
- cheeks,
- neck,
- shoulders,
- flanks, and/or
- hindquarters.
Caleonic colouration thus achieves whole-body conspicuousness.
In extreme cases, the 'lateralisation' of pale pelage reaches the dorsal surfaces of the rump, neck, and even back.
In this series of Posts, I hypothesise that a widespread species, the caribou (Rangifer tarandus, https://www.inaturalist.org/taxa/42199-Rangifer-tarandus) has
- certain subspecies with pied colouration (https://www.alamy.com/carribu-reindeer-rangifer-tarandus-caribou-image2513439.html?imageid=FAF39066-8FA2-4FFD-A129-1DC298D8D84F&p=17185&pn=12&searchId=1665bd569435214806da60bc576d4bf8&searchtype=0 and https://www.alamy.com/portrait-of-a-reindeer-walking-in-the-snow-alaska-usa-image364557768.html?imageid=DEE9244F-8F74-4688-BC41-A7D75C47B398&p=1311224&pn=1&searchId=8ebe633421a99c35728cae9a8c7eab8c&searchtype=0), and
- other subspecies with caleonic colouration.
This arguably makes R. tarandus the only species of mammal in which both patterns (pied and caleonic) occur, depending on the region/subspecies.
The only other species possessing caleonic colouration in only certain populations seems to be the domestic horse (Equus caballus). However, this may have arisen by hybridisation among several wild congeners, during the process of selective breeding (see https://www.inaturalist.org/posts/66546-a-hyperconspicuous-horse-hiding-in-plain-sight#).
The following show pied colouration in R. tarandus:
https://www.alamy.com/caribou-barren-ground-bull-autumn-denali-park-alaska-image219057000.html?imageid=CA708987-0B78-4D58-A301-7570ACD15211&p=365985&pn=3&searchId=8ef83f2f1de0431123cf39602bbd6277&searchtype=0 and https://www.alamy.com/stock-photo-caribou-rangifer-tarandus-bull-with-female-calf-on-migration-south-41499424.html?imageid=24FDBEC7-2515-4910-A5C6-57A0352BEF7C&p=54193&pn=3&searchId=8ef83f2f1de0431123cf39602bbd6277&searchtype=0 and https://www.alamy.com/stock-photo-caribou-rangifer-tarandus-bull-female-in-snow-on-migration-south-through-41499304.html?imageid=013FADBA-BE26-48E8-96CC-B83A1BEDFC74&p=54193&pn=4&searchId=53fe7e947085511a49c95d7dac229e54&searchtype=0 and https://www.alamy.com/caribou-barren-ground-bull-autumn-denali-park-alaska-image219057056.html?imageid=8BFBDFF1-5FE8-4504-BC54-0C1ED673978D&p=365985&pn=4&searchId=53fe7e947085511a49c95d7dac229e54&searchtype=0 and https://www.adfg.alaska.gov/static/home/library/pdfs/wildlife/caribou_trails/caribou_trails_2014.pdf.
The following seem to show caleonic colouration in R. tarandus:
https://www.mindenpictures.com/stock-photo-woodland-caribou-rangifer-tarandus-caribou-male-newfoundland-canada-naturephotography-image00596574.html and https://m.facebook.com/NewfoundlandLabradorTourism/photos/a.111088443781/111092763781/?type=3 and https://www.inaturalist.org/observations/9039103 and https://www.inaturalist.org/observations/91586926 and https://www.inaturalist.org/observations/38196369.
Pied colouration occurs in the autumn coat of most of the subspecies of R. tarandus, including R. t. groenlandicus and R. t. granti. The darkest features are arranged to provide dark/pale contrast, not crypsis or disruption of the outline of the animal.
These dark parts in this pied colouration are
- muzzle,
- forelegs,
- brisket/chest/lower shoulders, and
- lower flanks.
In the same figures, the palest features are
- nose (rhinarium),
- neck,
- beard/dewlap,
- tail, and
- the narrow area of pale on the rump.
In R. tarandus, caleonic colouration seems to occur in the subspecies found on two systems of islands, far apart geographically (https://en.wikipedia.org/wiki/Boreal_woodland_caribou#/media/File:Rangifer_tarandus_Map_NA.svg).
Firstly, on the island of Newfoundland (https://en.wikipedia.org/wiki/Newfoundland_(island)) occurs the subspecies R. t. terranovae (https://www.naturepl.com/stock-photo-woodland-caribou-nature-image00596572.html and https://www.shutterstock.com/de/image-photo/caribou-adult-female-rangifer-tarandus-avalon-1911012163).
Secondly (see part 2 of this series), on the Arctic islands of Canada occurs the subspecies R. t. pearyi (https://www.natureconservancy.ca/en/what-we-do/resource-centre/featured-species/mammals/peary-caribou.html and https://www.inaturalist.org/guide_taxa/1119027 and https://www.enr.gov.nt.ca/en/services/caribou-nwt/peary-caribou and https://www.alamy.com/stock-photo-bull-caribou-in-velvet-antlers-stands-in-the-colorful-autumn-tundra-75290355.html?imageid=89F3DD5C-43FB-48AC-B540-F92A8006B30D&p=228679&pn=25&searchId=9892403e79eeaa448727cb13a1e36c01&searchtype=0).
I agree with Valerius Geist that R. tarandus on the island of Newfoundland is quite distinct from other forms of ‘woodland caribou’, and that taxonomy took a wrong turn when R. t. terranovae was lumped with R. t. caribou.
The ‘woodland caribou’, in the western part of the boreal zone of North America, is unusually dark for the species (e.g. according to Valerius Geist). By contrast, R. t. terranovae is unusually pale - particularly considering that it lives at a far lower latitude than R. t. pearyi.
The following further illustrate R. t. terranovae: https://www.wildandexposed.com/journal/2018/10/17/marks-adventures-in-newfoundland
and https://mobile.twitter.com/NFLDdesigns/status/1339255210749865986/photo/1 and http://www.nlnature.com/Newfoundland-Canada-Nature/1520.aspx and http://birdingnewfoundland.blogspot.com/2009/12/southern-avalon-peninsula-birds-and.html and second photo in https://www.cbc.ca/news/canada/newfoundland-labrador/reindeer-deer-lake-video-1.4918560.
In the pied pattern, the lower flanks, chest, lower shoulders, and brisket are the darkest parts of the figure. This differs from the caleonic pattern in R. t. terranovae, in which these are the palest parts of the figure. Furthermore, a distinctive feature of R. t. terranovae is an individually variable diagonal border between relative dark and relative pale on the haunch (https://www.natureinstock.com/search/preview/woodland-caribou-rangifer-tarandus-caribou-bull-in-town-newfoundland-canada/0_10121446.html and http://conservationbiologynewfoundland.blogspot.com/2012/04/newfoundlands-wilderness-reserves.html).
Detracting from the caleonic pattern is the fact that some individuals of R. t. terranovae have a faint version of the flank-banding seen in other subspecies of R. tarandus.
However, this may perhaps be owing to some degree of anthropogenic mixing with another subspecies.
I hypothesise that the original appearance of the Newfoundland form was truly caleonic, to the exclusion of the flank-banding.
Wilkerson (2010, https://www.mun.ca/biology/scarr/Wilkerson%202010,%20excerpt.pdf) states that the domestic reindeer (R. t. tarandus) was introduced to the island of Newfoundland early in the twentieth century, and that there was indeed contact between this subspecies (which possesses flank-banding) and the indigenous populations, viz R. t. terranovae. I infer the possibility of hybridisation.
It is hard to see how the two patterns of colouration in R. tarandus, namely pied and caleonic, can be represented as extremes on a continuum. Instead, what seems to have happened is that, in an ancestral form,
- the whitish at the belly has spread so far up that it has replaced the entire flank-band complex of the pied pattern, while at the same time
- the legs have gone from basically dark to basically pale, and
- the neck has acquired a darkish dorsal (nuchal) zone.
It is this combination of pale flanks, pale legs, and a dark nuchal area that makes R. t. terranovae a candidate for caleonic colouration. The combination of extension of pale pelage on to flank and haunch, plus an overall pallour, set this subspecies apart from all other subspecies, besides R. t. pearyi.
However, the following three aspects detract from any simple characterisation of the colouration in R. t. terranovae as caleonic:
- some individuals do retain a faint version of the flank-banding typical of most subspecies of R. tarandus;
- the pale of the neck tends to be disjunct from the pale of the shoulders and flanks, separated by a more-or-less vertical tract of pale greyish-fawn pelage; and
- the pale of the lower haunch tends to give way, ventrally, to a darker tone on the upper hindleg, in some individuals.
What this means is that the pattern in R. t. terranovae - at least in its remaining, hypothetically hybridised form - is not categorically different from that in other subspecies.
In R. tarandus, any description of adaptive colouration must account for the seasonal cycle, in which the pelage moults. The moulting leads from this appearance (https://www.inaturalist.org/observations/137363786) to this (https://www.inaturalist.org/observations/73867876).
In winter, the pigmentation fades, owing to wear and weathering. The pelage then falls out in early summer, and re-grows from the darkly-pigmented skin. The colouration initially looks fairly uniform, before the full length of the hairs is achieved and the pigmentation differentiates.
Thus, the fully-differentiated colouration tends to be expressed in autumn, corresponding to the rutting season.
The following two male individuals, probably in September, show some features linking the ‘typical’ pattern above to the pattern typical of other subspecies of R. tarandus: https://www.alamy.com/stock-photo-two-caribou-rangifer-tarandus-forage-during-autumn-in-gros-morne-national-43870484.html. These include the relative darkness of the legs and the faint banding on the flank. These detractions notwithstanding, the colouration remains different from those of any other forms of ‘woodland caribou’ at the same season.
I take the following to be an adolescent male individual in autumn: http://www.hww.ca/en/wildlife/mammals/caribou.html. The side of the body shows a faint version of the banding seen in most subspecies of R. tarandus.
WINTER:
January: https://www.inaturalist.org/observations/85723506
March: https://www.inaturalist.org/observations/97411894
April: https://www.inaturalist.org/observations/43119657 and https://www.inaturalist.org/observations/73404224
SPRING:
Early May: https://www.inaturalist.org/observations/4829891 and https://www.inaturalist.org/observations/12796122 and https://www.inaturalist.org/observations/127414114 and https://www.inaturalist.org/observations/147676351
Late May: https://www.inaturalist.org/observations/1535227 and https://www.inaturalist.org/observations/120545240
Early June: https://www.inaturalist.org/observations/59202799 and https://www.inaturalist.org/observations/127339998 and https://www.inaturalist.org/observations/120600128 and https://www.inaturalist.org/observations/30141537 and https://www.inaturalist.org/observations/26703702 and https://www.inaturalist.org/observations/136693452
SUMMER:
Mid-June: https://www.inaturalist.org/observations/72014363 and https://www.inaturalist.org/observations/135072586
Late June: https://www.inaturalist.org/observations/87895806 and https://www.inaturalist.org/observations/69215843
Early July: https://www.inaturalist.org/observations/28248163 and https://www.inaturalist.org/observations/17045792
Mid-July: https://www.inaturalist.org/observations/14903618 and https://www.inaturalist.org/observations/128037050 and https://www.inaturalist.org/observations/130969801 and https://www.inaturalist.org/observations/2870518 and https://www.inaturalist.org/observations/146311257 and https://www.inaturalist.org/observations/28836472
Late July: https://www.inaturalist.org/observations/8063943
Early August: https://www.inaturalist.org/observations/91586926 and https://www.inaturalist.org/observations/73867876
Mid-August: https://www.inaturalist.org/observations/38196369 and https://www.inaturalist.org/observations/38195578
Late August: https://www.inaturalist.org/observations/33067919
AUTUMN:
Early September: https://www.inaturalist.org/observations/134114763 and https://www.inaturalist.org/observations/65690022
Mid-September: https://www.inaturalist.org/observations/65690664 and https://www.inaturalist.org/observations/75381992 and https://www.inaturalist.org/observations/99568979
The following (https://www.inaturalist.org/observations/28836472) seems to conform to caleonic colouration. However, once one understands the cycle of moult and regrowth of the pelage, it is obvious that the effect results mainly from the fact that the faded coat of the previous year has fallen out from the dorsal part of the figure first (as seen more clearly in https://www.inaturalist.org/observations/126510207).
to be continued in https://www.inaturalist.org/journal/milewski/67534-caleonic-colouration-in-the-caribou-part-2-rangifer-tarandus-pearyi-in-context#...