Archivos de diario de abril 2024

01 de abril de 2024

Caudal flagging in muntjaks (Muntiacus), relative to comparable bovids

Muntjaks (Cervidae: Muntiacus) occur in southern and East Asia. They are comparable with duikers (Bovidae: Cephalophus), which occur in Africa.

Muntiacus feae and

Muntiacus reevesi

Muntiacus vaginalis

However, there is a categorical difference between muntjaks and duikers, w.r.t. caudal flagging.

In muntjaks, the tail is relatively large, with white pelage on its ventral side ( and

The white extends variably around the perineum and on to the inner surface of the upper hind legs ( and

The white surface is starkly displayed by erecting the tail.

Muntiacus reevesi ( and

displayed when fleeing

displayed by infants and juveniles during suckling

Muntiacus vaginalis:

Publicado el abril 1, 2024 05:18 TARDE por milewski milewski | 27 comentarios | Deja un comentario

02 de abril de 2024

Why cross-walking gaits seem unrecognisably different in ruminants and like-size terrestrial monkeys

@matthewinabinett @jeremygilmore @tonyrebelo @variani18 @christiaan_viljoen @paradoxornithidae @beartracker @chewitt1 @gareth_bain

Please also see the following


A cross-walk is a diagonal walking gait, in which left fore tends to move together with right hind, and right fore tends to move together with left hind.

Among ungulates, a 'perfect' example is Hippopotamus amphibius (

Cross-walking occurs in certain small (body mass less than 35 kilograms) ruminants. More particularly, I refer to cover-dependent, nocturnal, solitary species with inconspicuous colouration (

However, a naturalist can observe these ruminants attentively without noticing that the gait is a cross-walk.

Furthermore, baboons (Papio spp.), macaques (Macaca spp.), and the proboscis monkey (Nasalis larvatus) - all of which habitually cross-walk on the ground - seem to have yet another different action ( and

However, here again, the gait is a cross-walk.

So, how can these disparate impressions be reconciled?


A problem in studying gaits is confusion of terms.

What I call a cross-walk is alternatively called a 'walking trot' or 'diagonal-sequence walk' (,opposite%20side%20of%20the%20body).

'Diagonal-couplets gaits' (see the reference above) include both a running gait (trot) and a walking gait (which I call a cross-walk).

What I call an amble is alternatively called a 'walking pace' or 'lateral-sequence walk'. In my terminology, just as a trot is the running version of a cross-walk, so a pace is the running version of an amble.

I have invented the term 'semi cross-walk' because


The aim of this Post is to explain why the walking gaits seem so different in ruminants and monkeys that it took me decades to realise that both kinds of mammals cross-walk.


Please compare

Which reader would have known that all of these photos illustrate cross-walking?

There are six main reasons why cross-walking in ruminants and monkeys seems to consist of categorically different gaits.

These are as follows.

In the ruminants,

Part of the reason why ruminants and monkeys deviate, in opposite directions, from the synchronous placement of the diagonally-opposite feet may be

In the ruminants in question, the rump is higher than the withers ( This is part of a 'hunched' conformation in which - presumably to boost acceleration when predators pounce - the hind legs are longer and springier than the fore legs.

In the monkeys in question, the rump tends to be lower than the withers (

This is because

Both the ruminants and the monkeys deviate from Hippopotamus amphibius, in which fore and hind legs are similar in length (


  • the proportionately long hind leg of the ruminants takes a long time to swing fully from lifting to placement, thus landing well after the diagonally-opposite fore leg, whereas
  • the proportionately short hind leg of the monkeys takes a short time to perform the analogous swing.

Finally, two relevant differences between the ruminants and the monkeys are that

  • in adults of the latter, cross-walking is categorically the only terrestrial walking gait; by contrast, most/all of the ruminants that cross-walk are capable of grading into a semi cross-walk when walking rapidly; and
  • when speeding up from walking to running, the former trot, whereas the latter immediately canter/gallop; indeed, no primate is known to trot.
Publicado el abril 2, 2024 02:27 MAÑANA por milewski milewski | 10 comentarios | Deja un comentario

06 de abril de 2024

Conspicuous colouration in Capreolus

There is a white patch on the hindquarters of Capreolus, in winter pelage.

This constitutes a flag if unexpanded (

The same feature constitutes a bleeze if expanded.

This is a difference of scale, effected by complex piloerection.

This piloerection occurs sometimes when the figure is stationary, and sometimes when the figure is fleeing.

Then feature in question can be called ischioperineal, because it is located on the buttocks and the perineum, which connects the left and right buttocks.

unexpanded, constituting an ischioperineal flag:

expanded, constituting an ischioperineal bleeze:

expanded or not, according to individual:

Publicado el abril 6, 2024 12:55 MAÑANA por milewski milewski | 25 comentarios | Deja un comentario

07 de abril de 2024

The pedaxillosternal flag of the Rocky Mountain mule deer (Odocoileus hemionus hemionus)

The Rocky Mountain mule deer (Odocoileus hemionus hemionus) is well-known to have a conspicuous pattern of colouration on the hindquarters.

This is most noticeable in the winter pelage, and in posteriolateral view ( and and and

However, what also requires description and explanation is a conspicuous pattern on the forequarters, which is most noticeable in profile and in a posture in which the inner foreleg is exposed.

The feature in question is complex, consisting of

In having a conspicuously pale inner surface, the foreleg differs from the hindleg (

In this and other ways, the pattern makes little sense in terms of countershading ( and and and

Publicado el abril 7, 2024 09:26 TARDE por milewski milewski | 27 comentarios | Deja un comentario

09 de abril de 2024

10 de abril de 2024

Impalas (Aepyceros) and giraffes (Giraffa) share the same walking gait, namely an amble

@beartracker @magcl @ptexis

It is widely known that the walking gait of giraffes (Giraffa) is unusual ( and

However, like many 'factoids' about Nature, this is subject to context.

It is true that giraffes have a 'parallel', not a 'diagonal', stride while walking ( and and and

However, the same is true also for many Carnivora.

The lion (Panthera leo), walking behind its intended prey, a giraffe, uses the same 'parallel' stride ( and and and

And, in turn, the lion walks similarly to the brown bear (Ursus arctos, and

(Yes, it is true that the brown bear walks like a giraffe, in the sense that the hind foot lifts only once the opposite fore foot has landed, and the hind foot lands (i.e. 'oversteps') considerably anterior to the print of the fore foot on the same side.)

Why is it, then, that this 'parallel' stride is seen as remarkable in giraffes, but not in Carnivora - including the domestic dog (Canis familiaris,

The obvious answer is:
because a gait that is normal in a plantigrade (e.g. brown bear) and digitigrade (e.g. lion) mammal seems much odder in mammals (giraffes) that are not only unguligrade, but extremely long-legged even among ungulates.

The above framing may explain, at least partly, why giraffes have a reputation for walking in an odd way.

For it is indeed remarkable that, in going from a 'flat-footed' animal, such as a bear, to an animal with 'stilts' for legs, such as a giraffe, the same gait is retained.
However, if this was a complete explanation, then all other hoofed mammals, including those with relatively short legs, would also walk like giraffes and Carnivora.

And this far from being true.

In fact, most ruminants walk in a different way, using a 'diagonal' stride. This applies to all deer (Cervidae, and many bovids (Bovidae,

Consider the tiger (Panthera tigris) following the sambar deer (Rusa unicolor) ( and and

The predator uses a 'parallel' stride ( and, whereas the prey uses a 'diagonal' stride ( and and

One explanation for this anomaly is as follows.

Unguligrady is an adaptation mainly for rapid and enduring fleeing from predators. In the 'arms-race' between prey and predator, hoofed mammals have compensated for the disadvantage of being surprised by predators, by having more efficient sprinting than that of Carnivora.

However, all benefits are accompanied by certain costs. And in the case of ruminants, a cost of 'living on stilts' (= unguligrady) is the risk of instability while walking.

Ruminants compensate for this risk by tending to use diagonal patterns in their walking strides.

This allows deer, for example,

It is only in two categories of ruminants that all 'diagonality' seems to have been abandoned while walking.

These are

  • giraffes, which achieve stability by means of the cantilever-effect of the long and massive neck, and
  • 'plains game', adapted to open environments where hiding is impractical, and compensating for this in various ways in their anti-predator strategies.

'Plains game' artiodactyls emphasise efficiency of walking over stability of walking. This is, hypothetically, why they use a 'parallel' stride, rather than a 'diagonal stride ( and,vid:-_if9UL39Lc,st:0). Their walking gaits are like that of giraffes, but for different reasons.

So, where do impalas fit into this conceptual framework?

Well, impalas walk like giraffes (

This can perhaps best be explained by comparing impalas with alcelaphin bovids (Alcelaphini).

Alcelaphins (wildebeests, hartebeests, and damalisks) epitomise 'plains game'. They are odd among ruminants in their combination of

  • humped withers,
  • migration/nomadism, and
  • extreme speed and endurance when galloping and cantering.

It is as part of the above syndrome that the 'parallel' stride of alcelaphins, when walking, can be considered. Alcelaphins are locomotorily aberrant, as part of an extreme relationship to predation.

For their part, impalas are odd among ruminants in their combination of

  • dependence on woody plants,
  • sedentariness (excluding nomadism, let alone migration),
  • intimate gregariousness, and
  • extreme bounding while fleeing.

We can, in light of the above, think of impalas as 'plains game adapted to relatively dense vegetation' (

This would place them - albeit with some 'sheohorning' - into the third category above, namely 'plains game'.

And this leads us to realise something shared by all the ruminants that use 'parallel' - as opposed to 'diagonal' - strides while walking, namely an inability/reluctance to use the ordinary running method known as trotting (

A trot is a 'diagonal' way of running. It is a standard gait in Carnivora and ungulates.

However, it is

  • absent in giraffes,
  • used by wildebeests and hartebeests only for display, and
  • peculiarly absent in impalas.

All of these ruminants have - in their own ways and for different reasons - abandoned trotting, as a gait for fleeing and commuting. It is in light of this common denominator that their adoption of a 'parallel' stride, when walking, can be appreciated.

What, then, should we call the 'parallel' gait used by giraffes, camels, 'plains game', and impalas alike?

I suggest that the best term is 'an amble'.

(This is not to be confused with a pace, which is also uses 'parallel' strides, but is a running gait, not a walking one.)

And this means that - to everyone's surprise - impalas and giraffes are evolutionarily convergent in ambling while walking ( and

This is despite the obvious differences between impalas and giraffes in

Furthermore, any preoccupation that giraffes walk oddly - which remains true in its way but is easily misinterpreted - may now have been overtaken. The more current notion - given the ordinariness of their body-proportions - should be that impalas walk even more oddly.

And this invites the next step in my investigative stroll, as follows.

Warthogs (Phacochoerus) - equally surprisingly - seem to amble (

This is in keeping with impalas inasmuch as these aberrant suids are 'plains game'. However, the new complication is that warthogs have certainly retained a trotting gait...

Please also see

Publicado el abril 10, 2024 01:22 MAÑANA por milewski milewski | 10 comentarios | Deja un comentario

11 de abril de 2024

Illustrations of the walking and stotting gaits of the pronghorn (Antilocapra americana)

@beartracker @maxallen @aguilita @jwidness @matthewinabinett @davidbygott @ptexis @taogirl @variani18


The pronghorn (Antilocapra americana) is renowned for its extreme speed and endurance when galloping - a topic which I do not address in this Post.

Instead, my aim is to illustrate the following, lesser-known gaits of the pronghorn, viz.

  • various walking gaits, and
  • various display gaits, the function of which is partly to signal individual fitness to predators and/or conspecifics.

The gaits of the pronghorn were well-documented more than 40 years ago (Bullock 1982, and and and and

However, it is only now that there are enough photos of this species on the Web to illustrate certain gaits clearly. The terms I use do not necessarily correspond to those of Bullock (1982).



Semi cross-walking: and




Scroll in

Scroll in


The pronghorn conforms to a category of ungulates that I have called 'plains game'.

This is because it combines the following features/traits:

Species of 'plains game' in the family Bovidae, in Africa and Eurasia, typically amble. I refer to all Alcelaphini and Hippotagini, and certain Antilopini, Reduncini, and possibly Caprini.

Based on its evolutionary convergences with 'plains game', we would expect the pronghorn to amble.

However, Bullock (1982) - despite the thoroughness of his study - did not find the pronghorn to amble.

So, is it true that the pronghorn is anomalous relative to bovid 'plains game', in lacking an ambling gait?

My study, as illustrated in this Post, offers a correction to Bullock (1982). In fact, the pronghorn does sometimes amble.

The pronghorn is partly aligned with Cervidae, a family in which ambling is absent in even those species

  • most resembling 'plains game', e.g. Cervus canadensis, and
  • with the most lateral placement of the eyes, e.g. Dama dama.

The following ( and and show the cross-walk typical of Cervidae.

On this basis, it would seem that the pronghorn incongruously combines cross-walking with extreme speed and endurance of galloping.

The diagnostic pattern of 'diagonal' walking gaits - including the cross-walk of the pronghorn - is that the hind foot lifts only once the contralateral foot lands, and the hind foot lands approximately in the track of the ipsilateral fore foot ( and and and and

Bullock (1982) documented that the pronghorn varies this in two ways, viz.

  • the hind foot lifts only once the contralateral fore foot lands (= what I term 'nearly ambling'), and/or
  • the hind foot lands slightly anterior to the track of the ipsilateral fore foot (possibly shown in

However, Bullock (1982) failed to document the full versatility of walking gaits in the pronghorn.

The following ( shows this versatility. The juvenile individual on the left is cross-walking, while that on the right is ambling.

In the case of 'display gaits', there is also something new to be investigated about the pronghorn. This is the possibility of two 'display gaits' additional to stotting (in the narrow sense).

These are

However, I have found few unambivalent illustrations of stotting/display gaits in the pronghorn, in either the strict or the loose sense. According to Bullock (1982), stotting is mainly an intraspecific (as opposed to anti-predator) display in the pronghorn, and observed mainly in the breeding season. However, this remains poorly documented photographically.

Stotting in the pronghorn is not as bouncy as in the sympatric Odocoileus hemionus hemionus. The footfall-pattern is similar, but the height is less.

It is remarkable that infants seem not to stot during play behaviour ( and

The pronghorn is extreme, among ungulates, in advertising itself by means of white piloerection of a bleeze on the hindquarters ( and and

However, any correlation between gait and the piloerection of this acetabulo-ischiopygal bleeze - which often occurs when the figure is stationary - is weak.


This investigation has raised three main questions about the gaits of the pronghorn, as follows. In this species,

  • under which circumstances does ambling occur?
  • why - in adaptive terms - has the pronghorn retained a cross-walking gait, despite otherwise conforming to 'plains game'? and
  • why does stotting occur mainly for intraspecific display and in adults, rather than - as in most other ruminants - mainly for anti-predator display and in infants and juveniles?

Also see

Publicado el abril 11, 2024 09:39 TARDE por milewski milewski | 49 comentarios | Deja un comentario

21 de abril de 2024

Is there subtle sexual dimorphism in the colouration of the ear pinna in the pronghorn (Antilocapra americana)?

In previous Posts, I have shown that certain species of Cervidae are sexually dimorphic in the colouration of their ears.

More particularly, mature males tend to lack certain conspicuously pale markings at/near the bases of the ear pinnae (

I have hypothesised that the loss of the markings in question, as males grow from juveniles to adults, may be related to the presence of antlers in males only. The showiness of these head-adornments theoretically eclipses any intraspecific communication via the swivelling movements of the ear pinnae.

Some semblance of this kind of sexual dimorphism may also occur in a few Bovidae. I refer particularly to Kobus kob (, which resembles cervids in that horns are restricted to males.

While scrolling through thousands of photos of the pronghorn (Antilocapra americana), I have come to suspect that the colouration of the ear pinnae of this member of the Antilocapridae is sexually dimorphic.

In this case it is dark, not pale, markings that differ. The tips and margins of the ear pinnae tend

  • to be accentuated by dark, short pelage in females and juveniles, but
  • to lack this accentuation in adult males - in which the dark horns draw attention undistracted by the ear pinnae.

The sexual dimorphism of the head adornments in the pronghorn is limited, because

  • the horns in males are smaller than in cervids of similar body mass, and
  • females, too, possess horns, albeit small and individually variable ones.

Furthermore, in the pronghorn the ear pinnae have a peculiar shape, suggesting a subtle 'mimicry' of horns. The tips are pointed and turned somewhat medially, which gives an impression of 'bracketing' the horns, in a way (

In cervids sympatric with the pronghorn, the anterior surface of the ear pinnae is conspicuously dark-edged in winter pelage. It is possible that a similar seasonal pattern applies to the pronghorn.

With the above in mind, I scrutinised the Web for illustrations of this sexual difference. The results are inconclusive, as follows.

Adult females and juveniles:

Adult males:

Publicado el abril 21, 2024 12:09 MAÑANA por milewski milewski | 10 comentarios | Deja un comentario

Additional illustrations of the differences in the ear pinnae of the two species of klipspringers (Oreotragus)

@variani18 @ludwig_muller

Please see

There are two species of klipspringer, not one.

Oreotragus oreotragus occurs in South Africa (Drakensberg, Karoo, Western Cape, Northern Cape, Namibia as far north as Windhoek).

Oreotragus saltatrixoides occurs in the rest of Africa, including Mpumalanga, Limpopo, and Northwest provinces of South Africa, and northwestern Namibia.


Orientation of ear pinnae vertical
Pattern on front-of-ear inconspicuous (= not qualifying as an auricular flag)


Orientation of ear pinnae horizontal
Pattern on front-of-ear conspicuous (= qualifying as an auricular flag) and

Publicado el abril 21, 2024 02:52 MAÑANA por milewski milewski | 8 comentarios | Deja un comentario

23 de abril de 2024

A new explanation for the hypercursoriality of the pronghorn (Antilocapra americana): selenium as a crucial micronutrient

The pronghorn (Antilocapridae: Antilocapra americana) is renowned for its extreme speed and endurance when running (

It is widely accepted that no animal on Earth exceeds the pronghorn in this combination.

Skeptical readers may perhaps suspect that the performance of the pronghorn my perhaps have been exaggerated.

However, the claims of speed and endurance are consistent with several other exceptional/extreme features, viz.

  • a consistent habit of opening the mouth while galloping,
  • long-range visual vigilance,
  • long-distance signalling by means of 'semaphoric' pale patches on the pelage, and
  • a lack - relative to other forms of 'plains game' - of displays of individual fitness to scanning predators.

All of the above add up to a syndrome of apparent 'hypercursoriality' in the pronghorn.

This syndrome seems incongruous, because the predatory regime in which the pronghorn lives is less, not more, intense than that pertaining to 'plains game' in Africa and Eurasia.

The long-range visual vigilance of the pronghorn is indicated partly by fully lateral placement of the eyes on the head, permitting the pronghorn to scan the horizon behind it as well as in front and to the sides.

However, this in itself hardly differs from 'plains game' in Africa and Eurasia.

What distinguishes the pronghorn are

  • extremely large eyeballs, both absolutely for a mammal and relative to body size, and
  • bony orbits that protrude from the skull laterally, to a degree possibly exceeding that in any other ungulate.

The long-distance signalling of the pronghorn is indicated partly by a conspicuously pale patch on the hindquarters ( and and

However, various other forms of 'plains game' have comparable features of colouration.

What is extreme in the case of the pronghorn is

The limited incidence of displays of individual fitness in the pronghorn is not categorically different from various 'plains game' in Africa. For example, Damaliscus spp. tend not to stot, despite being extremely cursorial among Bovidae.

However, what is odd in the case of the pronghorn is that

  • stotting, to the extent that it occurs among adults, is displayed mainly sociosexually, rather than to potential predators,
  • 'style-trotting' is rather poorly-developed, and
  • neither stotting nor proud-trotting occur in juveniles, even while playing.

This raises the question:


Publicado el abril 23, 2024 03:45 MAÑANA por milewski milewski | 31 comentarios | Deja un comentario