Bleezes, flags, and semets in the adaptive colouration of impalas (Aepyceros), part 1

@jandutoit @variani18 @nyoni-pete @tonyrebelo @jeremygilmore @matthewinabinett @botswanabugs @beartracker @simontonge @dejong @capracornelius @paradoxornithidae @muir

Also see https://www.inaturalist.org/posts/49665-the-peculiarly-complex-tail-of-impalas-aepyceros-has-several-caudal-flags-but-no-ischial-flag#

At first sight, impalas (Aepyceros) seem to be rather plain-coloured ruminants (https://www.inaturalist.org/observations/66064514 and https://www.dreamstime.com/closeup-impala-closeup-impala-scientific-name-aepyceros-melampus-swala-pala-swaheli-image-taken-safari-located-image200322382 and https://www.dreamstime.com/typical-male-impala-broadside-closeup-male-impala-scientific-name-aepyceros-melampus-swala-pala-swaheli-serengeti-image301832285 and https://www.alamy.com/masai-mara-impala-standing-in-the-park-image479285388.html?imageid=DEA64DC0-E980-45AF-AFFC-E63B7E1CB7B9&p=1889974&pn=6&searchId=0171166ff0fdcc816dc79c8195263b39&searchtype=0).

Furthermore, colouration is remarkably similar

• between the sexes (https://www.gettyimages.com.au/detail/photo/impala-family-royalty-free-image/1391649390?adppopup=true and https://www.alamy.com/stock-image-a-male-female-and-baby-impala-aepyceros-melampus-pause-for-an-informal-164664217.html and https://www.gettyimages.com.au/detail/news-photo/schwarzfersenantilopenbock-mit-weibchen-im-abendlicht-imm-news-photo/645833321?adppopup=true),
• between infants and adults (https://www.inaturalist.org/observations/163901096 and https://www.gettyimages.com.au/detail/photo/impala-and-fawn-royalty-free-image/1216744628?adppopup=true), and
• among individuals.

However, there are several medium- to small-scale patterns, which function mainly to accentuate postures and movements in social and sexual interactions, intraspecifically.

Indeed, impalas may perhaps possess

• more flags (which has a particular meaning in the terminology of adaptive colouration) than any other ruminants, and
• one of the clearest examples of a buccal semet.

BLEEZES:

There are no bleezes in impalas.

This can be illustrated by comparison with

• the springbok (Antidorcas marsupialis), which possesses a lateral bleeze (https://www.alamy.com/springbok-and-impala-at-watering-hole-in-etosha-national-park-namibia-image1936111.html?imageid=9F3EE547-CA7F-4C6D-A485-AF8526CDB57E&p=3663&pn=1&searchId=4dd898aca9c1f5238216f36748d13aa1&searchtype=0 and https://www.alamy.com/herd-of-springbok-antidorcas-marsupialis-single-impala-aepyceros-melampus-image5282436.html?imageid=0B527D9B-22F1-4864-B539-5CCD181A2CF9&p=69351&pn=1&searchId=4dd898aca9c1f5238216f36748d13aa1&searchtype=0 and https://www.alamy.com/impala-aepyceros-melampus-and-springbok-buck-standing-by-a-waterhole-image475377281.html?imageid=7072A59A-9F8D-416E-8930-FF8765FE4E62&p=59099&pn=1&searchId=4dd898aca9c1f5238216f36748d13aa1&searchtype=0 and https://www.alamy.com/stock-photo-four-black-faced-impalas-aepyceros-melampus-petersi-and-one-springbok-128615701.html?imageid=C3B40B92-6025-413B-9356-33269CFC0413&p=642197&pn=1&searchId=4dd898aca9c1f5238216f36748d13aa1&searchtype=0), and
• the bontebok (Damaliscus pygargus pygargus), which possesses an ischiopygal bleeze (https://www.dreamstime.com/bontebok-impala-botlierskop-reserve-south-africa-bontebok-botlierskop-private-game-reserve-mossel-bay-bontebok-image127611797).

LATERAL FLAG:

The lateral flag in impalas consists of a relatively pale, crisply-defined panel on the flanks, extending towards the scapula.

The pattern of pigmentation on the flanks is extremely consistent among individuals, and identical between the sexes. It can be thought of as the ultimate 'uniform' of adults of impalas.

In this respect, Aepyceros differs from Gazella and Nanger, in which the pigmentation on the flanks is individually (and in some spp. sexually) variable.

Despite this uniformity w.r.t. pigmentation, there is significant variation in appearance, depending on illumination.

When the pelage of the torso is piloerected (typically in the early morning light), the back and upper flanks are darkened by an effect converse to sheen (https://www.shutterstock.com/image-photo/young-female-impala-antelopes-safari-park-473817538 and https://www.dreamstime.com/african-impala-feeding-grasslands-savannah-south-africa-kruguer-national-park-very-fast-typical-antelope-image252124011 and https://www.sabisabi.com/discover/topics/impalas). This does not necessarily confer conspicuousness.

However, when the pelage of the torso is sleek in the heat of the day, the relatively pale panel on the flanks shows a sheen effect in certain illuminations. This 'pallid flank-band' may possibly be conspicuous enough to qualify as a flag.

There is a small patch of dark, bare skin at the stifle-fold (https://www.alamy.com/stock-photo-impala-ram-aepyceros-melampus-kruger-national-park-south-africa-55990976.html?imageid=B84F6F3F-A4BD-4811-9BE6-4910F1A97575&p=89162&pn=6&searchId=0171166ff0fdcc816dc79c8195263b39&searchtype=0 and https://www.shutterstock.com/image-photo/impala-177447278 and https://www.shutterstock.com/image-photo/female-impala-heard-wild-tanzania-africa-490988971 and https://www.alamy.com/stock-image-male-impala-standing-in-shade-facing-camera-169047114.html?imageid=E4DFD473-7DB4-4C76-9E38-DC07A444D884&p=359028&pn=1&searchId=2051f956df0f9901d2d41458e7158e6f&searchtype=0 and https://facts.net/nature/animals/18-facts-about-antelope/). The function of this is puzzling. However, it potentially serves to 'punctuate' the lateral flag.

https://www.inaturalist.org/observations/143987159

https://www.inaturalist.org/observations/10937414

https://www.dreamstime.com/royalty-free-stock-image-grazing-impalas-image17951726

https://www.dreamstime.com/impala-aepyceros-melampus-impala-aepyceros-melampus-herd-drinking-waterhole-masai-mara-park-kenya-image175559272

https://www.inaturalist.org/observations/4877608

https://www.inaturalist.org/observations/1500408

https://vaido.aminus3.com/image/2019-08-08.html

https://www.dreamstime.com/stock-photo-impala-antelopes-kruger-national-park-image64547334

https://www.gettyimages.com.au/detail/photo/male-impalas-royalty-free-image/820285962?phrase=african+impala&adppopup=true

The lateral flag is unapparent in wet weather (https://www.gettyimages.com.au/detail/photo/impala_3015_ma-royalty-free-image/520064866?adppopup=true).

ANTERIOR AURICULAR FLAG:

The anterior surface of the ear pinnae of impalas has a pattern of dark and pale (actually nearly black-and-white, https://www.dreamstime.com/impala-black-faced-aepyceros-melampus-petersi-image129022782 and https://www.dreamstime.com/stock-photo-female-impala-portrait-taken-nairobi-national-park-kenya-photograph-taken-face-has-wonderfully-soft-bokeh-image84212780 and https://www.dreamstime.com/royalty-free-stock-images-impala-wildlife-background-africa-funny-nature-ewe-chews-open-mouth-creating-image-fun-humor-as-seen-image35306109 and https://www.dreamstime.com/royalty-free-stock-photography-impala-ewe-portrait-image10434177 and https://www.alamy.com/female-impala-in-the-wild-image241774765.html?imageid=D9D12AC3-1E7A-4A65-AF44-143AB6B8EC8B&p=566502&pn=1&searchId=4dd898aca9c1f5238216f36748d13aa1&searchtype=0).

This is small-scale enough that it potentially contributes to camouflage-colouration (https://upload.wikimedia.org/wikipedia/commons/a/a9/Impala_ewe_behind.jpg).

However, it is large-scale enough to draw attention to the animal when the ears/head are moved on an otherwise stationary figure, in direct illumination.

The following nicely shows the difference between a carnivore, in which the front-of-ear has cryptic colouration, and an impala:
https://www.dreamstime.com/lion-walking-front-herd-impalas-lion-walking-front-herd-impala-chobe-national-park-botswana-image99984947

The following shows that the front-of-ear is more conspicuous than the pattern on the buttocks (https://www.istockphoto.com/photo/antelopes-in-the-kruger-national-park-south-africa-gm855954258-141001637?phrase=impala+calf&searchscope=image%2Cfilm).

https://www.inaturalist.org/observations/196171207

https://www.alamy.com/stock-photo-male-and-female-impala-aepyceros-melampus-kruger-national-park-south-44122171.html

https://www.alamy.com/impala-antelope-namibia-africa-safari-wildlife-image389173397.html?imageid=EA8B6637-5266-4FFD-8CF7-4EC6F189480A&p=836506&pn=8&searchId=a070cd5329fc32fad5b6e81e3528abb8&searchtype=0

https://www.dreamstime.com/lion-walking-front-herd-impalas-lion-walking-front-herd-impala-black-white-chobe-national-park-image99984945

https://www.dreamstime.com/lion-walking-front-herd-impalas-lion-walking-front-herd-impala-chobe-national-park-botswana-image99984934

https://www.dreamstime.com/impala-antelope-namibia-africa-safari-wildlife-family-aepyceros-melampus-caprivi-strip-game-park-nambwa-wilderness-image191497107

The skin on the front-of-ear is visible only when the whitish hair-panels piloerect to expose bare tracts. This occurs probably only in hot weather, when the radiative thermoregulatory mechanism is activated. The bare skin is then revealed to be flesh-coloured, not pigmented (Aepyceros petersi: https://www.alamy.com/black-faced-impala-etosha-namibia-august-2018-image398762437.html?imageid=18595578-042F-473D-9E0C-595D8F785C3C&p=557829&pn=4&searchId=f9415a767c0642ef78c594ff67510d1a&searchtype=0 and https://www.shutterstock.com/image-photo/impala-looking-straight-camera-kruger-national-1719317839).

POSTERIOR CORONAL FLAG:

This pattern is a function of sheen (possibly including ultraviolet), rather than depigmentation/pigmentation.

Please focus on the posterior surface of the crown of the head, plus the adjacent surfaces on the nape and the posterior of the ears, in https://www.youtube.com/watch?v=9CGoEJtE9X8.

Also please note:

• The posterior surface of the ear pinnae resembles the anterior surface in that the apex has dark, short pelage (https://www.inaturalist.org/observations/197638308 and https://www.gettyimages.com.au/detail/photo/impala-run-together-aepyceros-melampus-masai-mara-royalty-free-image/57255399?phrase=african+impala&adppopup=true and https://www.gettyimages.com.au/detail/photo/impala-herd-royalty-free-image/543976826?phrase=african+impala&adppopup=true).
• Most of the rest of the posterior surface is medium-tone, not white (https://www.dreamstime.com/stock-photo-red-billed-oxpecker-picking-parasites-impala%C3%A2%E2%82%AC%E2%84%A2s-ear-image53978260 and https://www.dreamstime.com/male-impala-chobe-national-park-botswana-aepyceros-melampus-northern-africa-image190341224 and https://www.shutterstock.com/image-photo/picture-beautiful-impala-antelope-behind-754645228).
• However, the dark apex of the back-of-ear is near enough to the sheen of the crown to produce some dark/pale contrast, accentuated by motion (https://www.dreamstime.com/lot-impala-antelopes-grass-landscape-kenyan-savanna-image148057442 and https://www.gettyimages.com.au/detail/photo/impala-tsavo-west-kenya-royalty-free-image/997672746?adppopup=true).

https://www.dreamstime.com/impala-looking-out-danger-image183413992

https://www.dreamstime.com/stock-image-impala-south-africa-s-image7623741

https://www.inaturalist.org/observations/155879893

https://www.inaturalist.org/observations/67574563

https://www.inaturalist.org/observations/91859769

https://www.inaturalist.org/observations/107525771

https://www.inaturalist.org/observations/172686553

https://www.inaturalist.org/observations/188096583

https://www.inaturalist.org/observations/174649718

https://www.inaturalist.org/observations/161370714

https://www.inaturalist.org/observations/152034681

https://www.inaturalist.org/observations/143987108

https://www.inaturalist.org/observations/127988480

https://www.inaturalist.org/observations/108123388

https://www.inaturalist.org/observations/124925975

https://www.inaturalist.org/observations/110006406

https://www.inaturalist.org/observations/105794590

https://www.inaturalist.org/observations/105452142

https://www.inaturalist.org/observations/98078027

https://www.inaturalist.org/observations/89832137

https://www.dreamstime.com/lot-impala-antelopes-grass-landscape-kenyan-savanna-image148056738

https://www.inaturalist.org/observations/7309291

https://www.inaturalist.org/observations/11069915

For comparison, the following show similar views but without the sheen effect:

https://www.dreamstime.com/royalty-free-stock-photo-african-impala-image9762415 and https://www.gettyimages.com.au/detail/photo/impala-mirror-reflection-royalty-free-image/98539628?adppopup=true and https://www.alamy.com/stock-photo-impala-aepyceros-melampus-females-masai-mara-game-reserve-kenya-88607324.html?imageid=F45D9D4C-FD25-4313-A080-6C07567FD7C1&p=269351&pn=12&searchId=7dc11c78361bd5df1ff35974e5ef97a8&searchtype=0 and https://www.alamy.com/stock-photo-female-black-faced-impala-lined-up-to-drink-at-waterhole-92886401.html?imageid=23535364-258D-46C0-A328-BBD180DCCFD9&p=45259&pn=2&searchId=1f5542e7213ab29c0373963d6ec132b5&searchtype=0 and https://www.dreamstime.com/stock-photo-impala-antilopes-national-park-masai-mara-kenya-image72425093 and https://www.inaturalist.org/observations/34869308 and https://www.inaturalist.org/observations/11187976

PEDAL FLAG:

The pasterns (https://en.wikipedia.org/wiki/Pastern) are whitish, the pallor resulting from both depigmentation and sheen.

There is an individually variable tendency - particularly in juveniles - to dark emphasis on the anterior surface of the fetlocks (https://en.wikipedia.org/wiki/Fetlock and https://www.dreamstime.com/stock-images-puku-image28618764 and https://www.dreamstime.com/royalty-free-stock-photos-puku-grazing-image28618738).

On the hindfeet, the metatarsal glands have dark tufts (https://www.shutterstock.com/image-photo/metatarsal-glands-on-impalas-back-legs-2337218443 and https://www.dreamstime.com/stock-photo-impala-legs-mkuze-national-park-south-africa-image54790604 and https://www.shutterstock.com/image-photo/metatarsal-glands-on-impalas-back-legs-2337218443 and https://www.inaturalist.org/observations/845707).

The fetlocks are dark at the positions of the (absent) false-hooves. The dark spot on each foot is medial (single not paired).

On the hindfeet, the dark spot on the fetlock connects with the dark of the metatarsal tufts. The resulting dark/pale contrast may accentuate the pedal flag when viewed from behind (https://www.istockphoto.com/photo/the-impala-is-a-medium-sized-african-antelope-ol-pejeta-conservancy-kenya-male-animal-gm1439084469-479434252 and https://www.alamy.com/female-impala-aepyceros-melampus-in-the-dessert-captive-distribution-africa-image565661183.html?imageid=EA3F40A5-8BFC-4747-8ACA-AC18FC5A0F95&p=816634&pn=1&searchId=2c70548f127dc53b817942155023dd85&searchtype=0 and https://www.inaturalist.org/observations/105527064).

The pedal flag is dependent on illumination. It is conspicuous mainly owing to

• the whitish appearance of the pasterns, and
• the motion of the feet.

However, a puzzling aspect is that the sheen is evident even in shade, as opposed to direct sunlight. This in turn suggests that the pedal flag may remain conspicuous at night. What kind of sheen-effect is this?

https://www.inaturalist.org/observations/149646826

https://www.inaturalist.org/observations/142370555

https://www.inaturalist.org/observations/142136628

https://www.inaturalist.org/observations/141892335

https://www.inaturalist.org/observations/132672095

https://www.inaturalist.org/observations/105527064

https://www.inaturalist.org/observations/101359100

https://www.inaturalist.org/observations/98197075

https://www.inaturalist.org/observations/73952189

https://www.inaturalist.org/observations/56613497

https://www.dreamstime.com/stock-photo-impala-antilopes-national-park-masai-mara-kenya-image72425258

https://www.inaturalist.org/observations/33839351

https://www.inaturalist.org/observations/10593664

https://www.inaturalist.org/observations/10525863

https://www.inaturalist.org/observations/8926845

https://www.inaturalist.org/observations/197879541

https://www.inaturalist.org/observations/197084898

https://www.inaturalist.org/observations/1380182

Aepyceros petersi: https://www.alamy.com/stock-photo-male-black-faced-impala-21848815.html?imageid=5AC181EF-09F2-4D60-BDF1-2A7081B3645C&p=16296&pn=2&searchId=1f5542e7213ab29c0373963d6ec132b5&searchtype=0

Aepyceros petersi: https://www.inaturalist.org/observations/108844718

to be continued in https://www.inaturalist.org/journal/milewski/89674-bleezes-flags-and-semets-in-the-adaptive-colouration-of-impalas-aepyceros-part-2#...

Posted on January 29, 2024 08:42 PM by milewski