Journal archives for February 2024

February 02, 2024

Annotated photos of impalas and other bovids mislabelled as impalas on the Web

There are tens of thousands of photos labelled as impalas (Aepyceros) on the Web.

I spent today trawling through them, with two search-images.

Firstly, I sought photos particularly illustrative of various features of adaptive colouration.

Secondly, I sought the valuable photos among those of other bovids mislabelled as impalas or in other ways - of which there are thousands in their own right. These photos have been effectively 'buried' in the electronic record, but here I bring some of them back out into the light.

The following shows the VERTICALLY-PILOERECTED CAUDAL FLAG in Aepyceros melampus. The shape formed by the white hairs of the tail is similar to that of a butcher's cleaver. Unlike other ruminants, A. melampus possesses not a tassel but instead a jointed feather-tassel. The joint defines the right-angle distally, and the metaphorical blade of the cleaver is formed by piloerection perpendicular to the lateral plane:

The following shows how completely the jointed feather-tassel of A. melampus can remain hidden (by a lack of piloerection), even when the tail is untucked:

The following shows the PENICILLATE CAUDAL FLAG in Aepyceros melampus. The distal joint in the jointed feather-tassel is open, without any other piloerection. In this case, the behaviour being flagged is micturition in adult males:

The following show the PEDAL FLAG of Aepyceros melampus particularly clearly. A main point to note is that, although impalas have distinct, complex, and subtle colouration, it is the pallor on the pasterns that advertise the figures:

Posted on February 02, 2024 01:48 PM by milewski milewski | 45 comments | Leave a comment

February 05, 2024


Posted on February 05, 2024 10:26 PM by milewski milewski | 0 comments | Leave a comment

February 06, 2024

Gaits and anti-predator displays, compared between deer (Odocoileus) in North America and impalas (Aepyceros) in Africa

There is an adaptive trend among the ruminants of the world, as follows.

Species adapted to dense cover tend to have

  • inconspicuous colouration (particularly on the hindquarters),
  • a halting gait, viz. the semi-crosswalk,
  • a lack of stotting (strenuous displays of individual fitness, dissuasive to scanning predators), and
  • non-gregarious society.

A typical example is bushbucks (Tragelaphus, and

By contrast, species adapted to short, sparse vegetation tend to have

  • conspicuous colouration (particularly on the hindquarters),
  • a smooth gait, viz. the amble,
  • stotting, and
  • gregarious society.

A typical example is the springbok (

Intermediate species show intermediate traits.

In the context of this adaptive axis, certain anomalies emerge. The following are prime examples.

Deer of genus Odocoileus in North and central America, and impalas (Aepyceros) in southern and East Africa, are comparable. Both fall into the intermediate part of the axis described above.

Both are associated with some woody cover, as opposed to treeless grassland. Accordingly, both are somewhat gregarious.

Both have

  • medium body mass (about 50 kg),
  • unremarkable body-proportions, and
  • fairly nondescript colouration on forequarters and torso.

However, two incongruities emerge, as follows.

Firstly, Odocoileus deer combine

  • a halting walking gait, linked to cover-dependence and non-gregariousness, with
  • conspicuous colouration on the hindquarters, linked to open environments and gregariousness.

By contrast, impalas combine

  • a smooth walking gait, linked to open environments and gregariousness, with
  • inconspicuous colouration on the hindquarters, linked to cover-dependence and non-gregariousness.

Secondly, both genera have stotting displays. However, the gaits used are surprisingly different.

Odocoileus deer display by

By contrast, impalas display by

Stating the puzzle concisely:
The deer referred to are incongruently demonstrative, whereas impalas are incongruently non-demonstrative.

Before attempting to explain this puzzle, let us examine the evidence by means of photos/video clips.

The following show the semi crosswalk, which is

  • associated with cover-dependent ruminants, and
  • in the case of Odocoileus has been 'exaggerated' into demonstrative walking.

What is remarkable is that a halting gait, allowing the animal to 'freeze' with two legs in the air in order to blend into the background when hearing or seeing something suspicious, has been converted from an adaptation for concealment to an adaptation for advertisement. This has been done not by changing the footfall-sequence, but by exaggerating the lifting/lowering of the feet into conspicuous movements, probably together with release of odour from the pedal glands.,vid:_9UiYWLW3aw,st:0,vid:r3qAhrvKi5I,st:0,vid:sXdOEAV_2w4,st:0

Posted on February 06, 2024 11:44 PM by milewski milewski | 56 comments | Leave a comment

February 10, 2024

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

...continued from


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 (

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 (

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

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 ( and and and

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

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.

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


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

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.

Gular semet:

There is a whitish patch at the crook-of-throat ( and and, which can be somewhat conspicuous in the limited context of masculine display, particularly roar-grunting (

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.


A noteworthy aspect of the adaptive colouration of impalas is that there are no auricular semets ( and and


The overall colouration of impalas is puzzling, because it conforms to neither crypsis nor camouflage ( and and

A case could be made that the overall colouration of impalas functions as 'gregarious camouflage' ( and and and and and

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. and and

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 ( and

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.

Posted on February 10, 2024 06:02 AM by milewski milewski | 23 comments | Leave a comment

February 11, 2024

Can precociality in the colouration of impalas (Aepyceros) be explained by their confusing nature as 'sedentary plains game'? part 1

@adamwelz @syddddney


The basic nature of impalas (Aepyceros) has been confusing for naturalists.

This is possibly because it has not been fully realised that impalas are 'plains game turned sedentary'.

In this Post, I explain the adaptive colouration of infants in this context.


The rationale goes as follows.

Impalas are associated with woody cover, rather than treeless grassland.

However, they conform with large ungulates of open, short vegetation in

At the same time, impalas differ from most other 'plains game' in a basic way, viz. in not being migratory/nomadic.

Instead, throughout their range, they are thoroughly sedentary ( and

Impalas achieve this sedentariness by resorting in the dry season to foods other than grass, particularly

What this means is that the well-known association of impalas with trees and shrubs may be misleading. Their 'cover-dependence' is trophic (, rather than anti-predatory.

Unlike reduncins ( and tragelaphins ( of similar body size, impalas are not 'cover-dependent' w.r.t. predators.

Instead, impalas are typical of 'plains game' in their

  • reliance on gregarious vigilance,
  • diurnal rather than nocturnal foraging, drinking, and parturition,
  • extreme gaits in reaction to predators, and
  • abandonment of concealment - even as infants.

Essentially, impalas have made a tradeoff, paying the costs (downsides) of certain benefits (upsides).

The main upside is the food provided by woody plants, obviating the need to shift location.

However, the main downsides are that

  • these plants provide cover not for the impalas, but for their predators, and
  • sedentariness exacerbates parasitism by ticks, mites, and flies.

The result of the unusual ecological strategy of impalas is a combination of biological traits that has confused naturalists in the past.

In this Post, I focus on only part of this confusion: that regarding adaptive colouration, and how it changes - or, more precisely, hardly changes - from youth to maturity.


The above characterisation provides a basis for assessing the adaptive colouration of infants in impalas.

In particular, it offers insight into their surprising emancipation from cover-dependence.

Unlike most 'plains game', adults of impalas do not have adaptively conspicuous colouration. I refer to dark/pale features so bold that they advertise the figures at distance.

Instead, their colouration is configured differently from both


Throughout this Post, I refer to Aepyceros melampus and Aepyceros petersi jointly, except where specified.

Infants of impalas have colouration similar to that of their mothers and fathers (

Impalas are unusual among the relatively large-bodied (body mass 50 kg or more) ungulates of the world - including most spp. of 'plains game' - in a certain way.

This is that the colouration of mature males is approximately complete already at birth, at least w.r.t. pigmentation, as opposed to sheen.

In other words, the pattern of pigmentation of the pelage in impalas is remarkably precocial.

However, not all features of colouration are equally well-developed in neonates.

Thus, a subsidiary aim of this Post is to document and illustrate these minor chronological (= ontogenetic) variations.


The lateral flag hypothetically facilitates the gregariousness of impalas, dependent on certain conditions of illumination.

This flag is undeveloped (i.e. present only in incipient form) in infants ( and and and and

This is in contrast to the pedal flag (see below).

In particular, the sheen effect is absent in infancy from the relatively pale panel on the flanks (

The following shows that, when the sheen effect is 'switched off', adults resemble infants in that the pattern on the flanks is subdued (

The 'punctuation' of the lateral flag, by a patch of dark, bare skin at the stifle-fold, is particularly lacking in infants ( and

On balance, the lateral flag is among the least precocial of the patterns described in this Post. However, it appears after only about one month of age ( and

It is possible that the difference between infants and adults, in the expression of the lateral flag, is owing largely to the proportional 'filling out' of the torso, as the animal progresses from milk to a bulky diet of grass.


The anterior auricular flag is hypothetically an anti-predator adaptation. It emphasises communication to the predator that it has been spotted, and has lost the advantage of surprise.

The anterior auricular flag of impalas is complete in infants ( and This precociality exceeds that of the dark stripes on the buttocks.


The posterior coronal flag hypothetically facilitates gregarious vigilance in impalas.

It is located on the highest part of the figure, and emphasise the orientation of attention/alarm, particularly as individuals raise their heads from foraging.

This is illustrated in the opening footage in,vid:ueMZh53DSBY,st:0.

Infants tend not to show the posterior coronal flag, even when the associated adults do show it ( and

However, the posterior coronal flag may be more precocial than the lateral flag.

In the following, sheen has appeared on the posterior surface of the crown of the head, at an age too young for it to appear on the flanks of the torso.

The following shows that a hair-whorl ( - which may perhaps help to explain the sheen effect - occurs at the location of the posterior coronal flag.

The following show the posterior coronal flag in adults. A main point to note is that, although there is a definite pattern on the buttocks, it is the pallor (owing to sheen) on the posterior surface of the crown that renders the figures conspicuous.


The pedal flag hypothetically facilitates gregariousness, particularly at night, when impalas tend to congregate on lawns.

This flag is peculiarly precocial (

It is fully developed in infants, despite

  • the lack of sheen elsewhere on the pelage of infants, and
  • the expectation that the metatarsal glands are relatively poorly-developed at birth. and and

to be continued in

Posted on February 11, 2024 01:11 AM by milewski milewski | 51 comments | Leave a comment

February 15, 2024

Can precociality in the colouration of impalas (Aepyceros) be explained by their confusing nature as 'sedentary plains game'? part 2

...continued from


The pattern on the buttocks hypothetically functions disruptively, i.e. in alignment with camouflage rather than advertisement.

This pattern - although individually variable - is one of the less precocial of the features of colouration in impalas.


Caudal flags in impalas hypothetically function mainly sociosexually.

The tail of impalas is similar in infants and adults ( and

As in adults, the tail is habitually tucked.

The stalk of the tail is slightly broader than in adults, proportionately to body size. The bare skin of the perineum is, accordingly, not fully pigmented in infants (

Infants cannot be said to possess any caudal flags beyond the penicillate caudal flag (

This is because the versatility of piloerection of the jointed feather-tassel/plume-tassel is not expressed in infancy. However, further study is needed of infants engaging in playful kick-stotting.

The following show that, in impalas, the tail is displayed by infants/juveniles during suckling:

Aepyceros petersi:


The buccal semet of impalas hypothetically functions to accentuate the movements of the mouth in rumination and grooming. This would facilitate gregarious vigilance.

This semet is exceptionally uniform among individuals, sexes, ages, and species of impalas.

The buccal semet is fully precocial ( and

The pattern of colouration at and around the mouth is complete at birth ( and


Impalas are unusual among ruminants in that their colouration at birth is similar to that in masculine maturity (

This is the result of both

  • the sexual monomorphism of impalas, in which males are similar to females in colouration despite possessing head adornments categorically absent from females, and
  • the precociality of impalas, which exceeds that of other 'cover-dependent' bovids as well as Cervidae in general.

This precociality is particularly noteworthy in the case of the pedal flag.

This is because the pedal flag is configured to function only in vegetation so short that the pasterns are fully visible.

This seems antithetical to the idea of infants hiding, by lying flat under cover, as happens in many spp. of ruminants.

Various spp. of 'plains game' are similar to impalas in forming 'creches' ( and

However, all of the other creche-forming spp. (e.g. Taurotragus oryx pattersonianus, Hippotragus equinus equinus, ?Damaliscus lunatus jimela) have infantile colouration different from that of mature males.

This 'intricate uniformity' seems consistent with the idea of 'gregarious camouflage' in impalas ( and

Posted on February 15, 2024 11:59 AM by milewski milewski | 19 comments | Leave a comment

February 16, 2024

A comparison between impalas (Aepyceros) of Africa and the blackbuck (Antilope cervicapra) of India

Impalas (Aepyceros) of southern and East Africa resemble - at least superficially - the blackbuck (Antilope cervicapra) of India.


Impalas are more massive than the blackbuck, somewhat undermining the validity of the comparison.

Furthermore, sexual dimorphism is less in impalas than in the blackbuck.


The normal walking gait in both cases is the amble.

In the blackbuck alone, mature males, in rivalry and courtship, use an exaggerated amble (which is actually more extreme than the walking gait of Giraffa).

Antilope, particularly showing ambling gait in masculine display:

In both genera, fleeing from predators includes spectacular bounding, as well as galloping (

Despite their similarity in bounding, the two genera differ considerably in their behaviour towards fences.

Impalas are surprisingly reluctant to jump over high fences, but are somewhat erratic, so that game ranchers confine them by means of fences 2.4 metres high. The blackbuck is decidedly reluctant to jump over even low fences ( and

Impalas are peculiar in not trotting, whereas the blackbuck - like all other gazelles - habitually trots (check).

Impalas have a kick-stotting gait (, whereas the stotting gait of the blackbuck is similar to that of diverse other ruminants.

Impalas swim poorly, whereas the blackbuck swims competently, like other gazelles (

Neither impalas nor the blackbuck use bipedal postures to forage.

Both genera lie by means of sternal recumbency. However, impalas, in adulthood, tend to lie mainly at night. By day they ruminate while standing (


In both cases, the ground-colour is medium-tone, with horizontal panelling on the flanks and crisply-defined white countershading in the ventral part of the torso.

However, a major difference is that duly males differ from adult females in the blackbuck.



Impalas are more gregarious than is the blackbuck. This is evidenced by the fact that founder populations of the former, e.g. in reintroduction programs, tend to fail unless several dozen individuals are present, whereas in the case of the latter only a few individuals are necessary. The two genera fare differently in captivity (e.g. in zoos) accordingly.

Texas introductions



Posted on February 16, 2024 04:27 AM by milewski milewski | 8 comments | Leave a comment

How do hippotragin bovids bite?

We do not normally regard ruminants as biting animals.

However, there is an intriguing possibility that the roan antelope (Hippotragus equinus) bites injuriously in self-defence.

The reasons why ruminants are associated with biting in self-defence are that they

  • have horns or antlers, plus hooves, all potentially effective as weapons,
  • lack canine teeth in most species, even in males,
  • lack upper incisors, which means that any 'bite' by means of the lower incisors would be relatively harmless, and
  • in the case of several clades, have gapes so tight that defensive biting by means of the premolars is impossible.

The domestic goat (Capra hircus) is known to bite humans. However, as far as I know it does so by means of its lower incisors, which are limited by the absence of upper incisors.

Hippotragus spp. have a reputation for pugnaciousness, both intraspecifically and anti-predator.

It is usually assumed that this involves only the horns. However, footage of a mature male individual of the sable antelope (Hippotragus niger niger) standing its ground against a group of the African hunting dog (Lycaon pictus) shows that the forehooves are flailed threateningly. And there is mention in the literature of the roan antelope (Hippotragus equinus) biting attackers.

What seems previously to have been overlooked is that hippotragins differ from most other bodies in that they possess a stretchy gape, allowing the biting off of fibrous food items such as grass culms. Unlike alcelaphins (all of which have tight gapes), hippotragins rely on plant matter some distance above the ground, not normally grazing on lawns.

The stretchy gape of hippotragins also allows the abrasion of bones in the mouth in osteophagy, a practice particularly frequent in this tribe owing to its tendency to occur on nutrient-poor substrates.

The stretchy gape of hippotragins is evident as a 'perverse smile' when the animals breathe heavily while running under duress.

Posted on February 16, 2024 11:21 PM by milewski milewski | 0 comments | Leave a comment

February 21, 2024

The puzzle of passive lingual protrusion in ruminants, part 1: first noticed in impalas (Aepyceros)

Recently, I noticed that impalas (Aepyceros) have often been photographed with the tongue protruding passively.

I do not refer to the active cleaning of the nostrils by means of the tongue ( and, which occurs in many ruminants ( and and and and and

Nor do I refer to the active tongue-flicking seen in hectic activities during masculine display in

Instead, I refer to the following:

Adult females: and and
Adult males:
Scroll to second photo in

Passive lingual protrusion in impalas seems odd, because it

Puzzles lie in the following questions, in order of increasing importance:

My curiosity piqued by the above, I began to search among other ruminants.

I found that many other bovids have, at least occasionally, been likewise photographed with the tongue protruding.


Tragelaphus euryceros:

Nyala angasii:

Strepsiceros strepsiceros:

Taurotragus oryx:

Bison bison:

Kobus leche: and

Kobus ellipsiprymnus:

Antidorcas marsupialis:

Nanger dama:

Budorcas taxicolor:

Ovis canadensis:

Capra ibex:

Capra hircus:

Oreamnos americanus:

Rupicapra rupicapra:

Cephalophus niger:

to be continued in

Posted on February 21, 2024 10:57 PM by milewski milewski | 69 comments | Leave a comment

February 22, 2024

A comparison of adaptive colouration between the common impala (Aepyceros melampus) and the European fallow deer (Dama dama)

Aepyceros melampus and

Dama dama

WITH DAMA DAMA IN SUMMER PELAGE (antlers still in velvet)

Features shared between A. melampus and D. dama:

Features differing between A. melampus and D. dama:

  • spotting absent in A. melampus, extensive on back, upper flanks, and haunches in D. dama
  • anterior/ventral surface of neck medium-tone in A. melampus, broadly pale in D. dama
  • anterior auricular flag present in A. melampus, absent in D. dama
  • posterior surface of ear pinna is broadly dark apically in A. melampus, plain-coloured in D. dama
  • pedal flag present in A. melampus, absent in D. dama
  • metatarsal gland-tuft conspicuously dark in A. melampus, inconspicuous in D. dama
  • posterior surface of ear pinna is broadly dark apically in A. melampus, plain-coloured in D. dama
  • flag absent on hindquarters (with relaxed tail) in A. melampus; ischiopygal flag present in D. dama
  • dark marking on crown present in A. melampus, absent in D. dama
  • buccal semet present in A. melampus, absent in D. dama
  • patch of bare (dark) skin at stifle-fold present in A. melampus, absent in D. dama
  • tongue dark in A. melampus, flesh-coloured in D. dama (

One of the greatest differences is that D. dama is more variable, in various ways, than A. melampus. This is true ontogenetically, sexually, seasonally, and individually. Dama dama is actually colour-polymorphic. The variation may originally have also been greater subspecifically. However, this is unknowable, because of the long history of anthropogenic influence on D. dama, all populations of which are now there because they have been put there by the human species.

Both spp. are extreme w.r.t. variation. Dama dama is exceptionally variable, even among deer, in terms of colour-polymorphism. For its part, A. melampus is exceptionally uniform, even among comparable bovids. and and and and and and and and and and and and and

Posted on February 22, 2024 11:39 PM by milewski milewski | 164 comments | Leave a comment