Bleezes, flags, and semets in the adaptive colouration of impalas (Aepyceros), part 2

...continued from https://www.inaturalist.org/journal/milewski/89191-bleezes-flags-and-semets-in-the-adaptive-colouration-of-impalas-aepyceros-part-1#

CAUDAL FLAGS:

Penicillate caudal flag:

The long white hairs of the tail of impalas are normally hidden, partly because they are folded and partly because the tail is tucked (https://www.gettyimages.com.au/detail/photo/leaping-impala-chobe-national-park-botswana-royalty-free-image/538630239?adppopup=true).

However, the long white hairs are exposed in several situations, viz.- when the tail is swished to shoo insects,

• during micturition and defecation, and
• by infants and juveniles during suckling.

In all these cases, the distal 'joint' on the tail is unfolded, extending the white tip, but the lateral hairs remain folded. This is what I call a 'penicillate' pattern (https://www.alamy.com/stock-photo-impala-male-aepyceros-melampus-cape-s-africa-12936370.html?imageid=A1D1CBEE-FAD2-4524-B369-BE802AB25F31&p=27299&pn=10&searchId=422524482389f4d1898ffb44225a4ddf&searchtype=0).

The following, of Aepyceros petersi, show how piloerection transforms the appearance of the tail in impalas:

• lateral long white hairs folded: https://www.alamy.com/stock-photo-black-faced-impala-escaping-from-danger-in-etosha-48448053.html?imageid=DB0D45E2-F327-4934-9037-AFEA80D19A41&p=163524&pn=11&searchId=3171fbca0bc4b0c09555c7c4a4e262c7&searchtype=0, versus
• lateral long white hairs piloerected: https://www.alamy.com/impala-males-sparring-aepyceros-melampus-etosha-national-park-namibia-image426416705.html?imageid=68527F02-9D6F-45A1-999A-F65ED4D3975A&p=18640&pn=10&searchId=f88dac56b555417b6a06fa62b13fef50&searchtype=0

https://www.dreamstime.com/amber-black-white-coloring-adult-male-impala-its-curved-horns-pondering-distance-tarangire-national-image134936351

https://www.inaturalist.org/observations/11072572https://www.inaturalist.org/observations/500032

Laterally-piloerected caudal flag:

The long white hairs are laterally piloerected during masculine display.

In Aepyceros melampus, which possesses a relatively small tail with a jointed feather-tassel, this gives the tail a shape resembling that of a symmetrical feather (https://www.alamy.com/stock-photo-impala-buck-with-tail-raised-and-making-sounds-territorial-behavior-48376563.html and https://www.dreamstime.com/male-impala-botswana-aepyceros-melampus-savuti-region-northern-africa-image190060019 and https://www.dreamstime.com/stock-photo-impala-male-bellowing-territorial-snorting-growling-roaring-exciting-his-harem-females-rutting-time-image84208595 and https://matirasafari.com/wp-content/uploads/2017/12/ME8A3771m.jpg).

In Aepyceros petersi, which possibly possesses a relatively large tail with a plume-tassel, the shape is fluffy rather than fan-like.

https://www.inaturalist.org/observations/197926724

https://www.inaturalist.org/observations/3431525

https://www.inaturalist.org/observations/6901419

https://www.inaturalist.org/observations/11238746

I have yet to see the laterally-piloerected caudal flag activated in females or juveniles. Females sometimes piloerect laterally while keeping the tail tucked. However, this does not have a conspicuous effect, partly because the spread long hairs - for some strange reason - do not appear white.

Vertically-piloerected caudal flag:

During kick-stotting, a shape reminiscent of a butcher's cleaver results from

• flexing of the distal 'joint' to a right-angle, and
• piloerection of the lateral long white hairs in a ventral, not lateral, orientation, so that the tracts on left and right sides of the tail converge into a blade-like surface.

https://www.alamy.com/impala-black-faced-aepyceros-melampus-jumping-high-etosha-national-park-namibia-africa-image440466092.html?imageid=50688ED7-5A71-4DC9-93F7-CB9731215001&p=2206959&pn=5&searchId=a128d0b9ff98444a3d95336675cd8ddb&searchtype=0

https://www.gettyimages.com.au/detail/photo/sprinting-impala-royalty-free-image/503017078?adppopup=true

https://www.inaturalist.org/observations/3739299

I am unsure whether mature males activate the vertically-piloerected caudal flag, even during kick-stotting.

BUCCAL SEMET:

The complex pattern on the chin, mandibles, and lips is small-scale, but crisply-defined, individually consistent, and different from that in any other ungulate,

This hypothetically functions to accentuate

• the chewing movements of rumination (https://www.dreamstime.com/impala-group-resting-impala-aepyceros-melampus-female-group-resting-ruminating-long-green-savanna-grass-kruger-national-image136523174), including at night, and
• the nibbling movements of the 'chin' when one individual grooms the pelage of another, a behaviour particularly well-developed in the impala.

This hypothetically facilitates social monitoring and gregarious vigilance.

A puzzling aspect of the colouration around the mouth, in impalas, is that the upper lip appears noticeably white only when viewed from the front, not in profile. This, like several other pale features in impalas, seems to reflect subtle and peculiar sheen-effects.

https://www.alamy.com/stock-photo-impala-aepyceros-melampus-oxpecker-sitting-on-impala-zimbabwe-76014030.html?imageid=C1520A05-D492-404D-B60C-2A0FA8F8FEF4&p=851480&pn=1&searchId=2c70548f127dc53b817942155023dd85&searchtype=0

https://www.dreamstime.com/royalty-free-stock-images-impala-image13351309

https://www.inaturalist.org/observations/9634

https://www.dreamstime.com/stock-photography-impala-wildlife-background-africa-fun-nature-ewe-chews-open-mouth-creating-image-humor-as-seen-image35412872

https://www.dreamstime.com/portrait-cute-wild-young-male-impala-aepyceros-melampus-nature-reserve-mara-north-conservancy-kenya-wildlife-image132878721

https://www.inaturalist.org/observations/10945099

https://www.alamy.com/impala-aepyceros-melampus-males-grooming-each-other-masai-mara-game-reserve-kenya-image262977047.html?imageid=C51F55F6-CE52-442E-AA83-3FAB2C5685D1&p=269351&pn=10&searchId=f88dac56b555417b6a06fa62b13fef50&searchtype=0

https://www.dreamstime.com/impala-black-faced-aepyceros-melampus-petersi-vrouwtje-close-up-kop-namibie-female-head-namibia-image129027529

https://www.alamy.com/stock-photo-blacked-faced-impala-or-black-faced-impala-aepyceros-melampus-petersi-74749154.html?imageid=CD8484B4-2478-4391-95D2-922B44C90F13&p=183828&pn=2&searchId=1f5542e7213ab29c0373963d6ec132b5&searchtype=0

https://www.dreamstime.com/stock-photo-black-faced-impala-etosha-national-park-namibia-image-image90011717

https://www.dreamstime.com/female-impala-aepyceros-melampus-portrait-kruger-national-park-south-africa-female-impala-aepyceros-melampus-portrait-kruger-image270426491

https://www.dreamstime.com/female-impala-aepyceros-melampus-portrait-kruger-national-park-south-africa-female-impala-aepyceros-melampus-portrait-kruger-image270426509

https://www.dreamstime.com/female-impala-aepyceros-melampus-portrait-kruger-national-park-south-africa-female-impala-aepyceros-melampus-portrait-kruger-image269672636

https://www.dreamstime.com/female-impala-aepyceros-melampus-portrait-kruger-national-park-south-africa-female-impala-aepyceros-melampus-portrait-kruger-image269672639

https://www.dreamstime.com/female-impala-aepyceros-melampus-portrait-kruger-national-park-south-africa-female-impala-aepyceros-melampus-portrait-kruger-image270428736

https://www.dreamstime.com/common-impala-kruger-national-park-south-africa-three-red-billed-oxpecker-grooming-common-impala-kruger-national-park-south-image291301703

https://www.dreamstime.com/stock-photo-fighting-impalas-image12091830

https://www.dreamstime.com/stock-photo-small-herd-antilopes-tarangire-tanzania-africa-image98512881

Gular semet:

There is a whitish patch at the crook-of-throat (https://www.dreamstime.com/stock-photo-impala-savanna-national-reserved-south-africa-kenya-image40584100 and https://www.inaturalist.org/observations/197961307 and https://www.alamy.com/stock-photo-black-faced-impala-portrait-of-careful-grazing-antelope-eating-tiny-52966912.html?imageid=6B3C7657-DF3E-4C77-8C06-E2909124802F&p=5021&pn=3&searchId=a5b956efd11b804f1481dd41761ad956&searchtype=0), which can be somewhat conspicuous in the limited context of masculine display, particularly roar-grunting (https://www.youtube.com/watch?v=IqzBw9EWhjU).

This patch is particularly noticeable in masculine maturity, relative to females and juveniles, because

• the throat is broadened, and
• the ground-colour of the neck is somewhat darkened.

However, the case for a gular semet is weakened by the facts that

• the pale feature in question is individually variable, rather than sexually dimorphic, and
• females do not have noticeable vocalisations.

https://www.alamy.com/stock-photo-male-black-faced-impala-challenging-another-male-in-the-etosha-national-138416866.html?imageid=D3A1E078-4C32-42EE-AF5A-0E3ED604E3FB&p=298586&pn=7&searchId=ae880af1fd61c0455cbecb5723d2b621&searchtype=0

https://www.dreamstime.com/impala-savanna-national-reserved-south-africa-kenya-animal-habitat-wildlife-scene-nature-image175021430

https://walkthewilderness.net/animals-of-africa-dominant-impala-behavior/

https://www.alamy.com/impala-aepyceros-melampus-young-male-grooming-a-female-nakuru-national-park-kenya-africa-image262992215.html?imageid=64908F75-77ED-426C-A7BB-D4C5258DF1F9&p=215444&pn=12&searchId=7dc11c78361bd5df1ff35974e5ef97a8&searchtype=0

https://www.dreamstime.com/stock-photos-male-impala-flehman-responce-image15033143

https://www.dreamstime.com/royalty-free-stock-photo-impala-showing-flehman-responce-botswana-image15518765

AURICULAR SEMETS:

A noteworthy aspect of the adaptive colouration of impalas is that there are no auricular semets (https://www.inaturalist.org/posts/55694-ten-best-illustrations-of-auricular-semets-in-deer# and https://www.inaturalist.org/posts/55639-auricular-semets-in-alces-and-odocoileus-but-not-other-odocoileine-deer# and https://www.inaturalist.org/journal/milewski/55532-previously-overlooked-facial-expressions-in-the-wapiti#).

DISCUSSION

The overall colouration of impalas is puzzling, because it conforms to neither crypsis nor camouflage (https://www.gettyimages.ie/detail/photo/impalas-in-south-africa-royalty-free-image/1187648715?phrase=impala+the+animal&adppopup=true and https://www.gettyimages.ie/detail/photo/impala-and-kudu-in-south-africa-royalty-free-image/1185776039?phrase=impala+the+animal&adppopup=true and https://www.gettyimages.com.au/detail/photo/giraffes-walking-to-the-forest-royalty-free-image/836319922?phrase=african+impala&adppopup=true).

A case could be made that the overall colouration of impalas functions as 'gregarious camouflage' (https://www.dreamstime.com/impala-aepyceros-melampus-impala-aepyceros-melampus-small-fast-antelope-african-savanna-tsavo-national-park-taita-hills-image111661427 and https://www.dreamstime.com/stock-image-herd-impala-aepyceros-melampus-image40133771 and https://www.dreamstime.com/herd-alert-female-impala-looking-camera-okavango-delta-botswana-herd-alert-female-impala-botswana-image129682758 and https://www.gettyimages.ie/detail/photo/herd-of-impalas-royalty-free-image/148092452?phrase=impala+the+animal&adppopup=true and https://www.gettyimages.com.au/detail/photo/herd-of-female-impala-botswana-africa-royalty-free-image/142025793?phrase=african+impala&adppopup=true and https://www.gettyimages.com.au/detail/photo/herd-of-impala-aepyceros-melampus-against-a-green-royalty-free-image/1313472400?phrase=african+impala&adppopup=true).

In 'gregarious camouflage', the disruptive patterns of colouration function

• relative to other members of the group, as opposed to the background/vegetation, and
• without the need to be stationary, or to 'freeze' in alarm.

https://www.gettyimages.com.au/detail/photo/herd-of-impalas-in-wilderness-royalty-free-image/561426203?phrase=african+impala&adppopup=true and https://www.gettyimages.com.au/detail/photo/impalas-royalty-free-image/561426993?phrase=african+impala&adppopup=true and https://www.gettyimages.com.au/detail/photo/impala-herd-royalty-free-image/561427575?phrase=african+impala&adppopup=true

https://www.gettyimages.com.au/detail/news-photo/impala-aepyceros-melampus-herd-of-females-in-grass-alert-to-news-photo/578257132?adppopup=true

https://www.gettyimages.com.au/detail/photo/herd-of-impalas-and-plains-zebras-royalty-free-image/534980932?phrase=african+impala&adppopup=true

https://www.gettyimages.com.au/detail/photo/male-impalas-and-topi-royalty-free-image/519948262?phrase=african+impala&adppopup=true

The colouration on the back-of-ear of impalas is puzzling.

This because:
the blackish of the distal third (a broadly apical feature) would seem to accentuate the ear pinnae, but in reality falls short of conspicuousness, because the rest of the posterior surface of the ear pinnae is not pale enough.

It is true that the dark marking on the back-of-ear is close enough to the sheeny crown to produce some tenuous dark/pale contrast. However, the puzzle remains of why the proximal two-thirds of the back-of-ear lack a significant sheen-effect (https://www.gettyimages.ie/detail/photo/high-angle-view-of-goats-walking-on-field-royalty-free-image/1306773451?phrase=impala+the+animal&adppopup=true and https://www.gettyimages.ie/detail/photo/herd-of-female-impala-in-serengeti-national-park-royalty-free-image/169566128?phrase=impala+the+animal&adppopup=true).

Why do impalas lack auricular semets, such as those seen in various genera of Cervidae?

The posterior coronal flag is one of the most unusual and subtle aspects of adaptive colouration in impalas. It is also the clearest example of the role of sheen in Aepyceros.

Publicado el 10 de febrero de 2024 a las 06:02 AM por milewski