The peculiarly complex tail of impalas: Aepyceros has several caudal flags, but no ischial flag

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INTRODUCTION

It has long been realised that the impala (Aepyceros melampus, https://www.inaturalist.org/taxa/42278-Aepyceros-melampus) is something of a 'living fossil', unrelated to antelopes of superficially similar appearance (http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532010000600017).

However, what seems to have been overlooked is the complexity of its tail, relative to other bovids.

What is unsurprising about the tail of the impala is that it is

However, what is surprising about the tail of the impala is that it

NEW TERMS FOR CAUDAL ANATOMY AND LOCOMOTION IN IMPALAS

I propose the following new terms for the distal structures, composed of long white hairs, on the tails of impalas:

  • jointed feather-tassel in the case of all forms other than petersi, and
  • ?plume-tassel in the case of petersi.

I am aware of the implication that petersi and nominate melampus differ categorically w.r.t. the anatomy of the tail. This needs further investigation.

However, the difference in the tails is great enough to suggest that the black-faced impala (Aepyceros petersi) is a separate species, not merely a subspecies. It differs so much from A. melampus that it might be called 'the fluff-tailed impala' (https://www.dreamstime.com/black-faced-impala-ram-showing-its-tail-northern-namibia-white-image204461845).

Furthermore, the enlargement of its tail is accompanied by depigmentation of the perineal bare skin (https://www.dreamstime.com/stock-photo-black-faced-impala-aepyceros-melampus-petersi-etosha-nationalpark-namibia-image90920112).

I have previously introduced the term 'kick-stotting' (https://www.naturepl.com/stock-photo-black-faced-impala-aepyceros-melamis-petersi-female-jumping-etosha-image01391643.html).

There are two different 'folds' in the jointed feather-tassel of Aepyceros:

  • immediately distal to the longitudinal dark stripe, there is a point of flexure, whereby the distal-most long white hairs can be folded back ventrally, and
  • to the left and right of the distal half of the same stripe, there is in each case a line of flexure whereby the long white hairs, arranged laterally, can be piloerected in either of two directions, viz. laterally or ventrally.

When the tail of the impala is flicked as part of the display during kick-stotting, a butcher's cleaver-like shape (https://www.youtube.com/watch?app=desktop&v=8sIYHSqaYKE) is produced by a combination of ventral foldings as per both the 'joint' described above, and the lateral lines of flexure.

The follwing shows the result (https://www.inaturalist.org/observations/102608195 and https://www.alamy.com/black-faced-impala-aepyceros-melamis-petersi-female-jumping-etosha-national-park-namibia-image262911368.html?imageid=142CA3C7-9E3F-4E77-BC7F-A26E31E76766&p=2080&pn=6&searchId=e9ed0bac00b4e168386089273c945e71&searchtype=0).

None of the above details seem to have been noticed previously by zoologists.

The following show the distal point of flexure in the tail-tassel of the impala:

https://www.dreamstime.com/impala-antelope-rooibok-africa-green-grass-trees-rock-g-image302969745

https://www.dreamstime.com/impala-antelope-rooibok-africa-green-grass-trees-rock-g-image302969728

The following (https://www.dreamstime.com/stock-photo-baby-impala-drinking-milk-mosi-oa-tunya-nation-park-zambia-africa-image61376242) shows lateral piloerection of the tucked tail.

CONCEALMENT VS ADVERTISEMENT

Impalas normally hide the tail, in at least three ways, viz.

More than in other ungulates including gazelles and the blackbuck (Antilope cervicapra, https://www.inaturalist.org/posts/47421-surprising-differences-in-displays-of-the-tail-between-the-blackbuck-and-other-gazelles), impalas tuck the tassel between the legs (https://www.inaturalist.org/observations/104194920 and https://www.inaturalist.org/observations/134246669 and https://www.inaturalist.org/observations/139050484),

This is consistent with the peculiar striped pattern on the buttocks and visible part of the perineum (https://www.inaturalist.org/observations/66513122 and https://www.naturepl.com/stock-photo-impala-tail-pattern-aepyceros-melampus-kruger-np-south-africa-nature-image01068237.html and https://www.dreamstime.com/stock-images-impala-rear-image1415424).

The bare skin on the perineum is dark in adults of melampus (https://www.dreamstime.com/stock-photo-young-female-impala-antelope-tarangire-national-park-tanzania-image49503539), but somewhat depigmented in adults of petersi (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).

The composite pattern helps to make the whole animal inconspicuous, in the sense of disruptive colouration (roughly equivalent to camouflage, https://www.inaturalist.org/observations/141866246).

Many ungulates have either

The following nicely show how inconspicuous the pale pelage on the buttocks is in the impala, compared with Kobus defassa: https://www.dreamstime.com/lot-impala-antelopes-grass-landscape-kenyan-savanna-image148057642 and https://www.inaturalist.org/observations/10565794.

However, the impala is unusual in blending into the surroundings by means of hindquarters marked similarly to the dark stripes associated with carnivores (https://www.inaturalist.org/posts/50603-predators-are-dark-spotted-but-their-ungulate-prey-are-pale-spotted-why#).

The following shows how inconspicuous the hindquarters are in the impala compared with a like-size gazelle (Nanger granti notata, https://www.inaturalist.org/taxa/568581-Nanger-granti-notata/browse_photos):
https://www.inaturalist.org/observations/103120232 and https://www.inaturalist.org/observations/7100460.

The habitual hiding of the white caudal hairs (https://www.inaturalist.org/observations/146773512 and https://www.inaturalist.org/observations/134246670) makes sense in this context.

The following reveals the shape of the jointed feather-tassel (folded and 'kinked') when the tail is fully tucked: https://www.inaturalist.org/observations/38667558.

PECULIARITY OF CAUDAL ANATOMY/PELAGE

The white of the jointed feather-tassel of the impala, in its penicillate form, seems almost luminous (https://www.inaturalist.org/observations/89817158 and https://www.inaturalist.org/observations/86665621 and https://www.dreamstime.com/male-impala-savannah-nairobi-park-central-kenya-image141664634 and https://www.inaturalist.org/observations/38566392 and https://www.inaturalist.org/observations/34029322).

I suspect that this is partly because

The impala displays its tail in sundry behaviours (https://www.wikiwand.com/en/Impala#Media/File:ImpalaSerengetiNationalParkMar2011.jpg).

In doing so it reveals the caudal anatomy/pelage to be unlike that in any other genus of ruminants.

The long white hairs are piloerected either

It is in the ventral direction that the vertical piloerection of the tassel occurs - unlike the tails of various antelopes, including gazelles, on which any vertically-arranged tomahawk-like hairs (usually black) are on the dorsal side.

The impala reveals the length and whiteness of the jointed feather-tassel when

However, in these cases there is no piloerection in either of the orientations described above.

DIFFERENCES BETWEEN THE TWO SPP. OF AEPYCEROS

The size of the tail differs to a surprising degree between the impala and the black-faced impala. I suggest that the shape/anatomy is also significantly different.

Relative to Aepyceros melampus, the tail of the black-faced impala (Aepyceros petersi (https://www.agefotostock.com/age/en/details-photo/black-faced-impala-aepyceros-melampus-petersi-adult-male-on-stony-ground-belling-etosha-national-park-namibia-africa/ZI6-2811268 and http://www.earthsendangered.com/profile.asp?gr=M&view=&ID=&sp=214)

Many species of ungulates show subspecific variation in various features. However, it is rare for the tail to vary much within a given species of bovid.

Furthermore, a difference apparently overlooked by everyone in the past is that, in adults, the bare skin of the perineum is somewhat flesh-coloured in A. petersi, as opposed to dark in melampus.

DOES THE IMPALA POSSESS CAUDAL OR ISCHIAL FLAGS?

The pattern on the buttocks is not conspicuous enough to qualify as a flag (https://www.inaturalist.org/observations/170454124 and https://www.inaturalist.org/observations/194016315 and https://www.inaturalist.org/observations/181234502 and https://www.inaturalist.org/observations/173501721 and https://www.inaturalist.org/observations/156355238).

The colouration of the tail of the impala is as unusual and complex, among ungulates, as that of the buttocks. However, it does qualify as a caudal flag (https://www.inaturalist.org/observations/187133577 and https://www.inaturalist.org/observations/152120947).

Caudal flagging in the impala occurs under various circumstances, including

However, it generally does not occur in running, whether the giants galloping or bounding (https://www.dreamstime.com/stock-photography-black-faced-impala-running-image12501592 and https://www.dreamstime.com/royalty-free-stock-image-impala-antelope-jumping-image2376656).

SUMMARY/CONCLUSIONS

What is noteworthy about the tail of impalas is that it

I suggest that the three different shapes of the jointed feather-tassel of the impala mean that we can recognise three different caudal flags in this species.

Also see https://www.inaturalist.org/journal/milewski/89191-bleezes-flags-and-semets-in-the-adaptive-colouration-of-the-impala-aepyceros-melampus#

Posted on April 18, 2021 11:47 AM by milewski milewski

Comments

Balanites glabra, shaped by Giraffa tippelskirchi:

https://www.inaturalist.org/observations/141892251

Posted by milewski 4 months ago

Then following, of Aepyceros petersi, shows the tip of the tail just anterior to the knee:

https://www.inaturalist.org/observations/133454963

In Aepyceros melampus, the tail is shorter than in A. petersi. Its tip is therefore completely hidden in profile view, when tucked between the legs in the normal way.

In A. petersi, the tail may cover the perineal bare skin more completely than in A. melampus:

https://www.dreamstime.com/stock-photo-black-faced-impala-challenging-another-male-etosha-national-park-namibia-image90694731

https://www.dreamstime.com/two-cute-cuddling-black-faced-impala-antelopes-aepyceros-melampus-brown-fur-white-belly-kalahari-desert-etosha-image224335179

https://www.dreamstime.com/herd-female-black-faced-impala-alert-all-looking-same-direction-very-as-if-have-seen-something-distance-image299104156

Posted by milewski 4 months ago
Posted by milewski 4 months ago
Posted by milewski 4 months ago

The following illustrates the 'best case' for an ischial flag in Aepyceros melampus:

https://www.inaturalist.org/observations/35914968

Posted by milewski 4 months ago

The following suggests that, in Aepyceros melampus, flehmen is not necessarily accompanied by display of the tail:

https://www.inaturalist.org/observations/7035201

Posted by milewski 4 months ago

A subtle difference between petersi and melampus is as follows.

Despite the dark markings in the face being emphasised in petersi, and despite the tail being particularly large in petersi, the vertical dark stripes on the buttocks of petersi tend to be narrower than in other sspp.

https://www.inaturalist.org/observations/197476007

https://www.inaturalist.org/observations/77839882

Posted by milewski 4 months ago

After scrolling through thousands of photos of Aepyceros melampus, I have started to form an impression that the tail is longer in East Africa than in South Africa, despite the subspecies being regarded, in iNaturalist, as nominate melampus in both cases.

East Africa:

https://www.inaturalist.org/observations/197154345

Posted by milewski 4 months ago

The following, of Aepyceros petersi, is fortuitously revealing, owing to back-lighting. It shows the size of the white tassel (which exceeds that in Aepyceros melampus) despite the fact that the taill is tucked.

https://www.alamy.com/a-herd-of-black-faced-impala-ewes-aepyceros-melampus-at-sunset-in-image152909317.html?imageid=D32B2294-2163-48C3-8D22-A13E8C65FF0F&p=183973&pn=6&searchId=e9ed0bac00b4e168386089273c945e71&searchtype=0

Posted by milewski 4 months ago

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