Adaptive colouration in Procapra

Having recently discussed the adaptive colouration of Saiga, I now scrutinise the antilopin genus Procapra (https://www.inaturalist.org/observations?taxon_id=42369).

This genus, like Saiga,

inhabits open environments in Eurasia, and
has colouration plainer (particularly in the case of Procapra gutturosa) than those of Antidorcas of southern Africa or Antilocapra of North America.

Procapra differs from most other antilopin bovids, in having seasonal variation in colouration. In this way, it seems to resemble cervids, rather than most bovids.

In various species of cervids, any conspicuous patterns are relatively muted in summer coat. The same may possibly be true for Procapra.

However, even in summer coat, Procapra is overall more conspicuous, to the human eye, than is Saiga.

The most important difference between Procapra and Saiga is that the former has a far more striking pattern of pale on the rump than the latter has.

There are other differences elaborated below, but these are relatively subtle.

PROCAPRA GUTTUROSA:

https://www.shutterstock.com/video/clip-3512249-mongolian-gazelle
https://www.shutterstock.com/video/clip-3512501-mongolian-gazelle
https://www.shutterstock.com/video/clip-3512870-mongolian-gazelle
https://www.shutterstock.com/video/clip-3512465-mongolian-gazelle
https://donachyblog.files.wordpress.com/2014/11/gazelle-bull-vocalizing-n.jpg
https://www.bbc.co.uk/programmes/p00380tj
https://animaldiversity.org/accounts/Procapra_gutturosa/
https://www.mindenpictures.com/stock-photo-mongolian-gazelle-procapra-gutturosa-herd-grazing-daurian-nature-naturephotography-image90789421.html
https://www.youtube.com/watch?v=gf0IsyhtapQ
https://www.youtube.com/watch?v=O9IowAlDbso
https://www.inaturalist.org/observations/117699694
https://www.inaturalist.org/observations/71237179
https://www.inaturalist.org/observations/40682531
https://www.inaturalist.org/observations/17349808
https://amurinfocenter.org/en/media/video/rare-birds-and-animal/volki-i-dzereny/
https://www.tnc.org.hk/en-hk/what-we-do/our-priorities/mongolian-gazelles/
Scroll in https://www.wildlifetoursmongolia.com/photo-gallery
Scroll in https://gryllosblog.com/2020/06/01/mongolia-part-2-the-gobi-desert-and-the-gobi-altai-mountains-22nd-26th-may-2018/
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This species has mainly plain colouration in human eyes. However, the pattern in P. gutturosa, in which the pale rump and haunch tend to catch the light relative to the back, is not consistent with cryptic colouration or countershading.

The pale patch on the rump of P. gutturosa is well-developed enough, in winter coat, to qualify as a bleeze. However, the rest of the colouration of this species is similar to that of Saiga in seeming plain. It would be interesting to compare the role of sheen in P. gutturosa vs Saiga.

The white patch on the rump in summer coat is too small and faint to qualify as a bleeze. However, it is better-developed than any comparable patch on the rump of Saiga in summer coat.

A subtle feature is the relative paleness (and sheen?) of the haunches, which suggests some evolutionary convergence with non-gazelle bovids such as Alcelaphus. This feature may perhaps be conspicuous in ultraviolet.

In P. gutturosa, the tail has no conspicuously dark feature (in contrast with the other two spp. in this genus). The following (https://www.sharperplanet.com/p825617885/h432B0F46#h432b0f46) shows that

the dark tuft on the tail is a minor feature in P. gutturosa (in contrast to the other two species in this genus, see below), and
there is no caudal flag when the animal flees from predators.

The following (http://daurzapoved.com/images/phocagallery/redkie_vidi/thumbs/phoca_thumb_l_pic6.JPG and http://media.gettyimages.com/videos/mongolian-gazelle-fawn-suckles-on-steppe-mongolian-steppe-video-id489298577?s=640x640) show that, in summer coat, the pattern on the rump of P. gutturosa is not conspicuous enough to qualify as a bleeze.

However, the sides of the animal (i.e. lower flank and haunch) are pale enough (perhaps partly owing to sheen) to contrast somewhat with the back, an effect at least as noticeable as that seen in Saiga in summer coat.

The following (http://www.marcelhuijserphotography.com/img/s/v-3/p1494599634-3.jpg) shows P. gutturosa in winter coat, in which the paleness of the haunch relative to the back and upper flanks is preserved.

The following (http://www.marcelhuijserphotography.com/img/s11/v28/p1494553850-3.jpg) shows the overall appearance, at some distance, of P. gutturosa in winter coat.

There is indeed a noticeable contrast between the white rump and the fawn back, and the pale area extends from the base of the tail forward along the haunch.

I have not seen an overall effect similar to this in Saiga in winter coat. However, I suspect that if Saiga were observed in ultraviolet as well as the wavelengths normally visible to the human eye, there would indeed be a similar effect.

During the rutting season, mature males show a parallel pattern to that of Saiga in similar condition: the sides of the neck become relatively dark (http://oopt.aari.ru/system/files/images/phoca_thumb_l_foto13.preview.jpg). Males at this time also tend to show a caudal flag, consisting of

the short tail, held horizontal, and
the dark snail skin, exposed by the raising of the tail.

The figures in the background show that the species is overall fairly conspicuous in its treeless environment. However, it is difficult to say whether Saiga would be less conspicuous in a similar illumination.

In summary so far, P. gutturosa

resembles Saiga in most aspects of its colouration, including seasonal and masculine coats,
hypothetically has an ultraviolet-reflecting bleeze on the haunch, that makes it conspicuous throughout the year in the eyes of ungulates and carnivores, and
differs from Saiga mainly in that it qualifies, in winter coat, for possessing a bleeze (pale) on the rump.

PROCAPRA PICTICAUDATA:

Now we turn to P. picticaudata (https://uk.inaturalist.org/taxa/42372-Procapra-picticaudata and https://bioone.org/journals/mammalian-species/volume-42/issue-1/861.1/Procapra-picticaudata-Artiodactyla-Bovidae/10.1644/861.1.full), which is named for the bold pattern of dark/pale contrast on its rump (https://www.flickr.com/photos/dave_irving/35597562192 and https://www.mindenpictures.com/stock-photo-two-female-tibetan-gazelles-procapra-picticaudata-rear-view-looking-naturephotography-image90684127.html).

The following (https://www.agefotostock.com/age/en/details-photo/tibetan-gazelle-4-females-procapra-picticaudata-china-tibet-altitude-4600m/AAM-AAES65216) shows the well-developed whitish patch on the rump, offset by the blackish tail. It also shows the rather conspicuous paleness of the forehead, which we do not see in P. gutturosa (above).

The following (http://cdn2.arkive.org/media/FD/FD73E0C2-E2C6-4E76-BFBF-DE71E08640CD/Presentation.Large/Female-herd-of-Tibetan-gazelles-.jpg) shows how conspicuous the rump bleeze is in P. picticaudata.

This rump bleeze is so well-developed that this pattern alone qualifies P. picticaudata as camposematic. Indeed, P. picticaudata is among the best examples in the whole family Bovidae of an extremely conspicuous rump.

The following (https://c1.staticflickr.com/3/2798/4390310798_ce4dbe8eaa_b.jpg and https://www.imago-images.com/st/0052135005) show that, in winter coat, P. picticaudata is overall dark enough to stand out from the snow. In this way it seems to differ from Saiga, which in winter coat seems pale enough that it does not necessarily stand out in a partly snowy scene.

I think it is possible that, like Connochaetes gnou, there is an ‘anti-sheen’ effect in the winter coat of P. picticaudata whereby the animal overall looks darker at distance than close-up.

The following (http://chinatibet.people.com.cn/mediafile/201112/20/P201112200832224958147761.jpg) shows P. picticaudata in summer coat.

There seems to be some downplaying of the rump bleeze at this season. However, in juveniles at least, this is compensated by the obvious ability to erect the whitish fur, much as in Antilocapra.

I do not know whether P. gutturosa can erect the pale fur on its rump. I doubt this.

The following (https://c1.staticflickr.com/5/4107/5086205412_3ec37ffe98_b.jpg) shows that the pattern on the rump of P. picticaudata, although downplayed in summer, remains overall conspicuous enough to qualify as a bleeze.

Also note the pale posterior surface of the foreleg. This is not explained by countershading, and is thus unlikely to be part of a cryptic (inconspicuous) pattern.

The following (http://www.cokesmithphototravel.com/image/58060318.jpg) of P. picticaudata in winter coat shows that, in addition to the rump blaze, there are at least two other conspicuously pale features: the pale forehead (not seen in P. gutturosa) and the pale upper legs. A sheen effect is suggested in the case of the latter.

The following (http://cdn1.arkive.org/media/7F/7F663560-13F0-4D1D-AD6D-18FC5AB66683/Presentation.Large/Two-male-Tibetan-gazelles-running.jpg) shows that even in adult males in winter coat, there is some ability to erect the whitish fur of the rump bleeze, to accentuate the display. Note the rather conspicuous paleness of the face.

The following (http://www.manimalworld.net/medias/images/goa.jpg) is a clear illustration of the erection of the white fur on the rump, reminiscent of Antilocapra. Again, note the paleness of the upper foreleg and forehead.

The following (http://www.cokesmithphototravel.com/image/58060309.jpg) shows how conspicuously pale the forehead is in P. picticaudata in winter coat.

The following (http://www.hughlansdown.com/photos/wildlife/mammals/tibetan-gazelle.jpg) is a good overall illustration of the whole-body pattern in this species in winter coat.

The following (http://www.nzmc.org/pic/20130408160833593.jpg) shows how dark the body of P. picticaudata can appear in winter coat.

This suggests that the winter coat is coloured to make the species conspicuous in snowy environments, rather than hiding it by means of paleness.

I have not seen a similar effect in Saiga, in which to the human eye the winter coat seems pale rather than dark.

The pale ventral surface on the body of P. picticaudata is not particularly extensive by antilopin standards. However, this paleness cannot be explained as countershading, because it functions somewhat parallel to the rump patch, in adding another aspect of dark/pale contrast.

One way to think of P. picticaudata is as an extremely cold-adapted gazelle which has emphasised its rump bleeze rather than the ‘wrap’ of ventral and inner-limb white as seen in e.g. Antidorcas, in keeping with the relatively dim light of its environment.

In summary of this species, P. picticaudata resembles P. gutturosa in having colouration less conspicuous, to human eyes, in summer than in winter. However, the difference is that P. picticaudata has a rump bleeze throughout the year, because