Journal archives for August 2021

August 02, 2021

Eye-white displays (starting with humans) and what we should call them, part 1

Everyone knows that in the human species the movements of the eyes can be expressive enough to outweigh the words spoken, e.g. when lies are being told. And that the sclera, i.e. the white of the eye, accentuates the tiny movements of the eyeballs, as if to spell out the unspoken messages in a rapid series of triangular flickers.

And many may have noticed that the selective breeding of the domestic dog has inadvertently made canine eyes more human-like in their expressions of emotion, partly by exposing the sclera (see and and and

What is less-known is that our closest relatives among the primates are not only unlike us in this way, they are in some sense the antithesis. They have a sclera so pigmented that it seems adapted actually to hide intentions and emotions, keeping the eyes inscrutable (see and and and and and

And that the eyes of hyenas are more expressive in the human sense than those of most other animals.

And that those large mammals which we humans tend to regard as rather expressionless may have analogous systems operating about their ears, which are far more mobile than human ears and more relevant to the sensory priorities of the species involved.

In this initial Post I illustrate some of these points, helping to put our human eye-white displays into a broader biological context. In later Posts I will propose the term 'scleral semets' for the features of adaptive colouration involved in communication by means of 'eye language'. And, as if by digression, I will return to the subjects of my most recent Posts, namely the felids, to listen to their ear-language with new eyes.

The following show how pigmented the sclera is in chimpanzees and gorillas, as if to achieve the opposite of the facilitation seen in humans: and

The following show the difference between the wolf, in which the sclera is tightly covered by the eyelids, and the domestic dog, in which the sclera is exposed: and and

The following show how much more of the sclera is visible in hyenas than in the wolf or most wild canids: and

The following show that the cheetah, unusually for felids, displays the sclera in fear:

Posted on August 02, 2021 03:09 by milewski milewski | 4 comments | Leave a comment

Eye-white displays and what we should call them, part 2

In the human species, eye-language works partly because the sclera is paler than the iris, the eyelids, and the eyebrows. 'Adaptive colouration' is involved, because without some degree of pale/dark contrast the subtle shiftiness of the eyeballs would hardly be visible even at conversational distances. Human scleral displays are therefore in principle similar to the many other small-scale social (intraspecific) displays found in various other mammals; and a scientific term should be aligned accordingly.

In a previous Post, I coined the term 'semet' for any feature of adaptive colouration which is too small-scale to be conspicuous to scanning predators, but conspicuous enough at close quarters to aid social communication. According to this approach, could we say that the human species possesses a 'scleral semet'?

To see how hidden the eyes of apes are by pigmentation of the sclera, compare with the albino version; and compare with

Although the apes generally lack any scleral semet, several species of monkeys resemble humans in this way: and and and and and and

Interpretation of scleral semets in monkeys is complicated not only because the phylogenetic sprinkling of these species seems so random but also because monkeys have other semets in which it is the eyelids that are conspicuously pale ( There thus arises a distinction between scleral semets and other types of ocular semets.

Certain species of baboons (Papio) exemplify this because they have pigmented, inconspicuous scleras but pale upper eyelids that are displayed by exaggerated blinking. Compare with and the more revealingly illuminated

Posted on August 02, 2021 10:12 by milewski milewski | 0 comments | Leave a comment

Three odd gaits in one brief video

Today I stumbled upon a video clip so packed with biological interest that I would recommend watching it before it vanishes from the Web:, the location being

We see an individual of the aardvark (Orycteropus afer, foraging in broad daylight, which is already exceptional because this is one of the most strictly nocturnal of large African mammals.

Then enters an individual of the brown hyena (Parahyaena brunnea,, an ostensible specialist on scavenging and an exceptional sighting in its own right although this species is not strictly nocturnal.

Bear in mind that the protagonists are about like-size (brown hyena adult averages 40 kg), but with divergent morphological specialisations. The aardvark is the largest specialised eater of termites and ants on Earth, with extremely muscular legs and large claws. The brown hyena has bone-crushing teeth (see and extremely economical hindquarters in which the shortness of the hind feet is compensated by extreme swing of the tarsal joint ( The aardvark is designed to dig extremely rapidly whereas the brown hyena is designed to walk long distances on an empty belly.

Action: the brown hyena chases the aardvark at full sprint, apparently intent on killing it in defiance of any reputation as a mere scavenger. Can the bite of this 'postcarnivore', unaccompanied by any sharp claws, possibly subdue such nuggety prey?

The brown hyena catches up, but the aardvark manages to somersault down a hole, frustrating the would-be killer. Then, a group of the blue wildebeest (Connochaetes taurinus taurinus), an odd-looking species in its own way, chases the brown hyena off the scene, in a surprising show of aggression towards this 'mere scavenger'.

What interested me particularly is that this footage revealed one new gait every minute. These species can all gallop, but they are strangely divergent in the sequence of limb-movements when not sprinting - perhaps because they are so peculiar morphologically that they look like chimeras.

The aardvark seems like a badger-on-ballet-shoes with a conical tail, a tubular snout and hare-like ears. The brown hyena has a strangely sloping back and long neck, nosferatu-ears, and a cross-grained cape-like mane. The blue wildebeest also has a sloping back and a strange mane and tail. And each is odd in its locomotory gearing, although not necessarily rhyming with reason.

The aardvark is perhaps the only fully terrestrial, digitigrade mammal which uses a perfect cross-walk, the legs moving in diagonal pairs (see and This has not been pointed out in the literature but is obvious once one develops a search-image for walking gaits.

The brown hyena has its own odd walk in that the 'hock' seems hypermobile (see and But what is really unusual is that, instead of trotting like other carnivores, it paces like a camel. (Watch for this after the aardvark vanishes and the brown hyena gives up on digging.) Also see

And, for its part, the blue wildebeest is also more reluctant to trot than most other ungulates, gearing up from a walk straight into a canter (see for a different species of wildebeest).

So here we have an expose of specialised gaits which have yet to be explained in adaptive terms. The aardvark has slowed down the trot to convert the same limb-movements into a walk. The brown hyena has speeded up its walk in replacement of any trotting gear. And the blue wildebeest has just skipped the trot, going from first gear straight to third.

'Go figure'.

Posted on August 02, 2021 11:47 by milewski milewski | 2 comments | Leave a comment

August 03, 2021

Felid 'eyespots' are like human eyes, but not in the way you think

Everyone knows that part of the language of human facial expression is the flickering of the eye-whites as our gaze shifts, indicating changes in attention and emotion.

And most realise that one of the reasons why cats seem inscrutable is that their eye-whites are covered by their eyelids (e.g. see and and

However, what tends to be overlooked is that the swivellings of the ear pinnae in cats might be similarly informative to the swivellings of our eyeballs - if only we humans possessed the mental 'software' to decode these messages coming from our pets (e.g. see

The idea is this: when individuals within a given felid species communicate face-to-face, they use a language of facial expression analogous to ours; it is just that whereas in humans 'the eyes have it', in felids 'the ears have it'.

But this idea gets even more intriguing. It is the paleness of the human sclera that makes it easy to track the movements of our eyeballs relative to our pigmented facial skin/eyebrows.

Could it be that an important aspect of the graphic patterns on the back-of-ear of most species of felids (albeit excluding the domestic cat) is partial visibility from in front, punctuating the ear-language by means of the same principle of small-scale pale/dark contrast?

The crucial fact is that when felids experience fear or anger they 'frown with their ears' by turning the ear pinnae backwards, displaying part of the back-of-ear to the front. And thus arises the possibility of auricular semets (see my Journal Post of May 13, 2021, titled 'Introducing conspicuous patterns about the ears of ungulates'

This shows the ears of the tiger (Panthera tigris) turned towards the viewer: And this shows how the white spot on the back-of-ear becomes visible with a turn of one of the ear pinnae:

It is not new to compare the back-of-ear pattern with 'eyespots'. The name 'ocelli', which means 'little eyes', has even been used (e.g. see But most previous explanations of the pattern seen in and and have been rather fanciful: a way for mothers to lead infants, or even a way to scare off enemies creeping up from behind.

In the following and, the expression could show slight fear/annoyance or merely a shift of attention to a sound coming from behind. Presumably members of a given felid species can make these distinctions much as we humans can differentiate between a lying eye-shift and an innocent sideways glance: context plus subtle differences of expression elsewhere on the same faces.

The following photos of the serval (Leptailurus serval) show how the 'eyespots' shift partly into view with a turning-back of the ear pinnae: and and and In all cases, these are presumably informative expressions to members of the same species. To the human viewer, there seems to be merely a shift of attention rearwards in most of these; only in the last photo is there apparent emotion.

However, to the felid viewer, emotion may be evident in the first three as well. The difference in mental 'software' between us and the felid is that it takes the fang-baring expression for us to detect the annoyance - whereas in the eyes of felid mates/kin the slightest annoyance might be communicated by the auricular semet alone.

Posted on August 03, 2021 22:04 by milewski milewski | 9 comments | Leave a comment

August 05, 2021

If felid eyespots lead offspring, why are they already present at birth?

As I mentioned in my latest Post, it is sometimes suggested that the eyespots on the back-of-ear of felids have evolved to help the mother to lead her infants. However, a glance at and should cast doubt on this idea.

The colouration of most species of felids is precocial, with most of the markings already present at birth. This includes the back-of-ear pattern.

Lynx rufus and and and and

Leptailurus serval and and and and

Panthera tigris and and and and and

Panthera onca and and and

Leopardus pardalis and and and

Puma concolor and

It seems that in all felid species possessing a back-of-ear pattern, the pattern occurs in infants as well as in adults. Furthermore, the pattern is always, as far as I know, as clear in adult males as in females, despite the fact that felid fathers never lead infants.

Of course, it remains possible that the back-of-ear patterns of felids - like most features of organisms generally - combine several adaptive values. However, would it be safe to say that leading offspring is not one of them?

Posted on August 05, 2021 15:12 by milewski milewski | 0 comments | Leave a comment

August 06, 2021

Who has seen a fang-baring puppy?

Something struck me for the first time today: felids fang-bare from infancy onwards, whereas canids do not.

In the many species of wild cats which have fang-baring expressions, it is easy to find photos of infants and juveniles 'fang-baring before they have fangs'.

Examples are:

the puma ( and and and,

the Eurasian lynx (,

the caracal ( and,

the lion ( and and and,

the leopard ( and,

and the cheetah ( and and

However, in the few species of canids which have fang-baring expressions (virtually restricted to the genus Canis, see and, these displays seem relatively late to develop ( and

Furthermore, in those species of felids in which bold facial colouration produces a 'warpaint' effect accentuating the fang-baring expression, this is so precocial that it is present already at birth.

By contrast, infantile facial colouration in the genus Canis usually differs from that in adults ( and and and and and and

Perhaps infants and juveniles of wolves, jackals and the domestic dog are rarely seen fang-baring because sociality in canids usually involves a strict hierarchy in which insubordination is not tolerated. Is so, felids follow different rules: the sociality of the lion seems to have made no difference to the readiness of infants and juveniles to fang-bare.

Given that infant felids begin to fang-bare long before their teeth present a credible threat, what adaptive value is there in the precociality of fang-baring expressions and displays among felids?

One possible explanation is that the claws are already well-enough developed in infants to present a credible threat, that infants of felids have extremely precocial co-ordination of the scratching reflex, and that the facial display is an indirect reminder of the claws.

Another possibility is that, in resembling adults so precisely (except for the presence of significant canine teeth), infant felids display as a way of reminding would-be attackers of the identity of the mother, which may be about to arrive and certainly does present a credible threat.

Posted on August 06, 2021 11:07 by milewski milewski | 4 comments | Leave a comment

August 07, 2021

Why Lupulella adusta could be called the baffledog

The mainly nocturnal side-striped jackal (Lupulella adusta, and blends into the background, even by day (see and

However, the patterns of its colouration suggest an anti-predator strategy based on 'buying time with confusion' once spotted.

The appearance of this species is so individually and ontogenetically variable that - given its secretive ways and sparse populations - the superior predators in its habitat are unlikely to be able to recognise it immediately. This would tend to stall any attack, giving the side-striped jackal precious seconds to slip away.

First let us look at individual variation in the tail, which includes bushiness (e.g. see, darkness, and the presence of a pale tip.

There is a large pale tail-tip in and and and and and

By contrast the pale tail-tip is absent in and and and and and and and

Let us turn now to the individual variation in the pattern on the flank and haunch.

In some individuals there is virtually no banding: and In others there is a definite pale band sandwiched between two dark bands: and

Other individuals again show various combinations and intermediate patterns. The pale band varies in shape and orientation.

The following illustrate these bewildering variations, which only partly correlate with subspecies: and and and and and

There is also independent variation in the presence and shape of a subsidiary pattern on the haunch: and

Finally turning to ontogenetic variation, the following show how different juveniles look from the adults above: and and and and

The two species of Lupulella differ in their dependence on cover, their times of activity, and their diets. Both have odd colouration - particularly on the flanks - for canids. However, the conspicuous colouration of L. mesomelas ( and makes sense for a partly diurnal species of open vegetation, which tends to hunt relatively large prey cooperatively.

In the case of the timid, omnivorous side-striped jackal, the oddness is mainly in the inconsistency - which has the opposite effect from promoting rapid recognition. This 'baffledog' seems to play on the likelihood that superior predators will not yet have formed an appropriate search-image, while at the same time boosting the number of encounters needed for them to form this search-image.

Posted on August 07, 2021 09:01 by milewski milewski | 23 comments | Leave a comment

August 09, 2021

The facial ruff in lynxes as an alternative form of facial flag

The facial ruff, which occurs in two genera and five species of felids, is hard to interpret adaptively.

The facial ruff seems superfluous to camouflage, and risks being conspicuous to prey during stalking. It seems to be a social or sexual adornment, but is unlike the lion's mane because it is present in females as well as males.

The range of forms of the facial ruff within the genus Lynx can be seen in

Besides lynxes, the facial ruff occurs only in the tiger, and is best-developed in the smallest, Sumatran, subspecies (see

A key to understanding the facial ruff could be as follows:

  • in several other species of felids, there is a subtle facial flag consisting of whitish upper lips, lower lips, chin and throat,
  • this pale region breaks the camouflage pattern enough to gleam conspicuously when the head is held high, and
  • at the same time this pale region, associated with the mouth, can be hidden by lowering the head, while the eyes maintain a clear view.

What all the felids possessing the facial ruff have in common is that the mouth is as camouflaged as the body, with dark spots/stripes on the upper and lower lips. One of the subtle peculiarities of lynxes is that the lips are camouflaged (see

The conspicuous region has been transferred to the facial ruff instead. (The Eurasian lynx is something of an 'exception which proves the rule' because its facial ruff is proportionately small, and sure enough its whitish chin is free of spots/stripes:

On this basis I hypothesise that at least one of the functions of the facial ruff is to act as a facial flag for social purposes.

The following show how conspicuously pale the mouth region of the European wild cat (Felis silvestris) can look: and

The following show the same effect for the jungle cat (Felis chaus): and and and and

The following shows - for particular comparison with the tiger - a similar effect in the lion:

The following photos are arranged by species, sex and ontogenetic stage of development. They show that lynxes and the tiger conform approximately to a pattern in which the mouth region is inconspicuous (being spotted/striped) but the facial ruff is relatively conspicuous. This is mainly because the facial ruff is pale, but also because it is accentuated with dark markings.

Lynx canadensis adult and and and

Lynx canadensis 9 months old

Lynx lynx adult and and and and

Lynx pardinus adult male

Lynx pardinus adult female

Lynx pardinus adult and and and

Lynx rufus and and and and

Panthera tigris sondaica adult female and male together

Panthera tigris sondaica adult female and

Panthera tigris sondaica adult male and and and

Panthera tigris sondaica and and and and

Lynx canadensis infants and juveniles and and and

Lynx rufus infants and juveniles and

Panthera tigris sondaica infants and

Posted on August 09, 2021 00:35 by milewski milewski | 0 comments | Leave a comment

The forearm flag of felids as a retrievable ancestral feature depending on the local predatory regime

In a previous Post (July 31, 2021, 'Forearm flags and caudal flags in lynx-like felids'), I showed that the bobcat (Lynx rufus) and the serval (Leptailurus serval) possess forearm flags, which ostensibly function as warning colouration nested within the overall camouflage colouration.

A trace of the forearm flag is visible in many other genera and species of felids. It thus seems to be an ancestral feature, which can remain latent. When a population finds itself, through the contingencies of biogeography, in a predatory regime intense enough for the warning insignia to be genetically 'switched on' again, a resumption of the dark/pale contrast relative to the overall colouration needs little more than increased pigmentation/depigmentation.

The genus Felis is like the genus Lynx in showing this latency. Felis contains various populations, ranging from subspecies to species, in which the forearm flag has been reinstated in at least a proportion of individuals.

A prime example is one subspecies of the African wild cat (Felis lybica), the species from which the domestic cat (Felis catus, see and has been derived. The inner foreleg is barred in several domestic breeds and in all wild subspecies, but is usually not noticeable relative to the overall colouration.

It is only in Felis lybica griselda, the wild cat of the Kalahari (Botswana and Namibia), that the forearm flag is expressed in virtually all individuals. This is possibly because the predatory regime relative to the available resources is particularly intense there (e.g. see

Here is the forearm flag in action:

It so happens that Felis lybica griselda is the best-illustrated of all the subspecies of this species. The following show the forearm flag clearly:
third photo in and and and and and and and and and and and

Turning now to other species of Felis, the same theme of latency and ambivalence is apparent.

In the European wild cat (Felis silvestris) only a few individuals qualify for a forearm flag:

The jungle cat (Felis chaus) seems to be at an evolutionary threshold between a conspicuous pattern and an inconspicuous one, or vice versa; and it also shows wide individual and possibly regional variation. Although the species fails to qualify for a forearm flag, it illustrates the latency in the pattern. The range in expression is between and

In Felis margarita, an unknown percentage of individuals qualify for a forearm flag: and

Let us now turn to other genera of felids, with an eye to the same incipient/residual pattern on the inner foreleg.

In Puma concolor, the incipient/residual pattern is restricted to juveniles; there is no forearm flag despite the development of warning colouration on the face: and and

Some individuals of Lynx canadensis, L. lynx and L. pardinus show the incipient/residual pattern in adults: and and and and and and and and and However, I have yet to see any individual of these three species in which the forearm flag is expressed on a par with 80% of individuals in Lynx rufus.

In the caracal (Caracal caracal), the incipient/residual pattern is visible in only a few individuals: and The closely related African golden cat (Caracal aurata) is particularly variable in colouration but the pattern is never bolder than in

Finally for now, the following are worth examining:
Prionailurus planiceps
Prionailurus bengalensis
and Leopardus geoffroyi and

Posted on August 09, 2021 06:02 by milewski milewski | 7 comments | Leave a comment

August 10, 2021

Is there any trace of a forearm flag in the largest felids?

We have seen, in two recent Posts, that at least seven genera and 15 species of felids share barring on the inner foreleg, which differs from the pattern on the inner hindleg as well as, in some cases, being incongruously bold relative to the camouflage-effect of the overall colouration (e.g. see

All of these are small to medium-size except for the puma.

Our explanation for this pattern is that small felids are vulnerable to large felids and hyenas. Where the predatory regime is most intense it may pay to express the latent conspicuousness of the inner foreleg in the form of warning colouration.

How can we test this explanation? One way is to see if the largest felids, which are at or near the top of the predatory hierarchy, lack the aforementioned latency. For the explanation to be borne out, the 'big cats' should have patterns on the inner foreleg which are completely congruent with the camouflage colouration, lacking any incipient/residual trace of barring and also being consistent with the inner hindleg.

The cheetah is low in the predatory hierarchy. However, we can include it here because it is as large as the leopard, the snow leopard and the puma.

Please see the photos below, which show that in most of the 'big cats' there is a slight tendency for the inner surfaces of the legs to be striped - or at least for the spots to be aligned - even where the colouration on the torso lacks any striping. This makes it important to compare fore- and hindlegs.

On this basis, I see no potential for warning colouration on the inner foreleg in lion or snow leopard.

There is slight potential in the leopard because of a tendency for the spots to be more aligned on the inner foreleg than on the inner hindleg (an extreme example is

In the tiger, the similarity between inner fore- and hindleg in striping might rule out any latency for warning colouration, were it not for the intriguing facts that a) the ground-colour is white on the inner foreleg vs fawn on the inner hindleg, and b) the outer foreleg tends to be free of striping. All that would be needed for a forearm flag to be expressed in e.g. or is a dimming of the general striping and a widening of the dark stripes on the inner foreleg to form bold barring.

The jaguar is ambivalent in a different way. The pattern on the inner foreleg is more complicated and more individually (and regionally?) variable than in the closely-related leopard.

It is intriguing to find traces, however ambivalent, of a potential for warning colouration in both jaguar and puma (see and and and This is because these species, across the Americas until about ten thousand years ago, were vulnerable to carnivores larger than not only themselves but also the extant lion in Africa and India. I refer to Smilodon populator, Panthera atrox and several particularly large, short-faced bears (Arctodus and Arctotherium).

The cheetah, perhaps surprisingly, shows little potential for any barred pattern on the inner foreleg: at best a slight alignment of the spots in some individuals.

In summary, only lion, leopard, snow leopard and cheetah emerge as categorically lacking any latent pattern for the forearm flag. Jaguar, puma and even tiger retain ambivalent patterns, notwithstanding the difficulty of imagining any biogeographical situation in which the tiger could have found itself low in the predatory hierarchy.

Lion and and

Tiger and and and and and

Leopard and and and and and

Jaguar and and and and

Snow leopard and and

Cheetah normal morph and and and and and and and

Cheetah 'king' morph and and and

Posted on August 10, 2021 13:59 by milewski milewski | 0 comments | Leave a comment