Journal archives for March 2021

March 06, 2021

Extreme sexual incongruity in the adaptive colouration of the blackbuck (Antilope cervicapra)

In its colouration, the blackbuck (Antilope cervicapra) of India seems to function as two incongruous species in one (see

The blackbuck is a gazelle, phylogenetically and ecologically.

However, females and juvenile males lack the conspicuous dark/pale contrast on the hindquarters that is seen in gazelles of the genera Gazella and Eudorcas.

At the same time, mature males are more extensively dark than any other gazelle (see and

Among gazelles, conspicuous colouration is correlated with gregariousness in open environments, where hiding from predators seems to be less successful than the self-advertisement of alertness and locomotory fitness.

The hindquarters tend to have bold patterns of dark (tail-tassel and pygal bands) and pale (buttocks and escutcheon), which stand out in posteriolateral view even when the animals stand still. The display is accentuated by movement of the tail and flaring of white on the buttocks, particularly when the animals stot in demonstration, to any scanning predator, of a current capacity to flee so rapidly and enduringly that pursuit of the individual in question would likely be futile.

The ecology and behaviour of the blackbuck would predict more-or-less normal colouration for a gazelle. After all, this species is in line with other gazelles in being gregarious and living in treeless grassland.

The blackbuck stots with vigour and versatility: it

Furthermore, the blackbuck is capable of flaring the white of the buttocks, and erecting the tail (see and

However, the patterns typical of gazelles have been lost in an extreme sexual dimorphism in the blackbuck. Males become more conspicuous than any gazelle as much of their body turns blackish in maturity (see and and

This pattern has little relationship with predation, and instead functions in masculine rivalry and courtship (see and

For their part, females and juveniles (see and have lost all the noticeably dark features of gazelles (flank-band, pygal bands and tail tassel).

And the tail, having lost its tassel, is usually left inert in gaits and situations in which it would be flicked or erected demonstratively in other gazelles.

The only conspicuous aspect of colouration in females and juveniles of the blackbuck is the ventral whitish, which extends higher than in any other gazelle on to the elbow region and the ventral surface of the neck (see and

This in itself is a puzzling pattern, partly because it has been lost in the southern- and easternmost populations.

In mature males of the blackbuck, the effectively black-and-white colouration seems superfluously conspicuous to predators. In females and juveniles, the colouration is incongruous in a converse way, because no other gregarious species gazelle living in the open, and frequently stotting and bounding, has colouration lacking all dark features.

And since the sexes live together most of the time, we are left with an overall puzzle.

Regardless of whether the females and juveniles can blend into such exposed environments, their presence is likely to be divulged anyway by the outlandish appearance of the mature males among them.

So, how does the overall colouration of the blackbuck function in a single adaptive strategy with respect to predation?

Posted on March 06, 2021 02:58 AM by milewski milewski | 0 comments | Leave a comment

March 08, 2021

Surprising differences in displays of the tail between the blackbuck (Antilope cervicapra) and other gazelles

All ruminants with visible tails can swish or flick the tail, to shoo insects attracted to the anus and vulva.

However, gazelles and their relatives (tribe Antilopini, are surprisingly variable in the other uses of their tails, along lines which I have not seen mentioned in the literature.

Let me start with the genera Gazella, Eudorcas and Antilope.

Gazelles and their relatives display their tails mainly

  • in reaction to the appearance of potential predators, and
  • in social interactions within the group.

These categories naturally tend to be blurred in playful behaviours that serve to rehearse reactions to danger.

Most species of Gazella and Eudorcas tend to wag the tail conspicuously, as soon as they go from standing to walking and trotting. They then relax the tail again when galloping (e.g. see Gazella gazella in

One way to interpret this is that the animals are signalling to the potential predator (including photographers) that the individual is energetic and alert, and thus not worth singling out for pursuit.

However, Gazella subgutturosa ( and Gazella marica ( tend not to move the tail until running. Thereupon, it is held more decidedly erect than in other gazelles (see

And Antilope tends to leave the tail inert throughout the locomotory sequence of reaction to potential predators (see, even sometimes when stotting (see and

The contrast can be illustrated by comparing Eudorcas thomsoni ( with Antilope cervicapra (

Thomson's gazelle wags its black, long-tasselled tail with particular zeal when milling hesitantly in view of a safari vehicle (e.g. see

By contrast, no amount of nervousness will get the blackbuck to wag its nondescript tail - which lacks a noticeable tassel - in similar circumstances.

Instead, the blackbuck tends to express its tension at a whole-body scale, by leaping high into the air (see Such high leaping is never seen in Thomson' gazelle.

Where the blackbuck - which is the most sexually dimorphic of antilopins - does display its tail is in masculine behaviour (rivalry and courtship, extending to lekking).

Here, the adult male 'hypererects' the tail so that its tip touches the rump (see and

This looks more like an olfactory than a visual display. This is because the tail tends to be rather redundant in the whole-body showiness of the black-and-white masculine figure, as he walks with an unusual gait - which seems close to a 'perfect amble' ( and and

However, nobody seems to have found a scent-gland under the tail in the blackbuck. The displays, and lack thereof, of the tail thus remain an odd aspect of this species.

Also see

Posted on March 08, 2021 11:33 AM by milewski milewski | 10 comments | Leave a comment

March 31, 2021

Conspicuous features of colouration in giraffes (Giraffa spp.)

Inconspicuous colouration allows large mammals to be overlooked by predators. However, it is possible for these animals to communicate socially by means of flags - small-scale conspicuous features arranged on the figure so as to be displayed discretely to companions without negating the overall crypsis/camouflage.

The location of flags on particularly mobile body-parts such as the ear pinnae, feet and tail allows such communication to be activated by movement, and de-activated when the animal 'freezes' in stationary self-concealment.

Because giraffes (Giraffa, see are the largest land mammals with camouflage-colouration (, their flags potentially facilitate communication over distances of hundreds of meters.

A CAUDAL FLAG in giraffes - consisting of a black tail-tassel - is activated by vigorous movement of the tail, particularly while the animal is running ( and

However, the pale flags of giraffes are relatively subtle, because they depend on sheen effects and can be activated by slight movements.

A noteworthy aspect of these pale flags is the variation among the species and subspecies of giraffes.

The only pale flag common to all species of giraffes is an auricular flag. In the case of Giraffa reticulata (see and this is the only conspicuously pale feature on the whole figure, viewed from any angle.

The following shows the caudal and auricular flags in action simultaneously, which again enhances conspicuousness because of the contrast between dark and pale:


The auricular flag in giraffes consists of a pale, sheeny surface on the back-of-ear ( This accentuates the movement of figures walking away from the observer. It is relatively poorly developed in Giraffa tippelskirchi tippelskirchi (in which the sheen effect seems weak) and Giraffa camelopardalis peralta (in which the pale feature seems hardly noticeable given that the whole head tends to be pale, see

Giraffa camelopardalis rothschildi

Giraffa tippelskirchi tippelskirchi

Giraffa tippelskirchi thornicrofti

Giraffa giraffa giraffa


A laryngeal flag, consisting of a pale tract between the crook of the throat and the base of the ear, occurs in several forms of giraffe, subject to individual variation. It is clearest and most consistent in Giraffa tippelskirchi.

The laryngeal flag works in conjunction with a conspicuous paleness on the cheeks that occurs in several forms of giraffe, subject to individual variation and illumination (e.g. and and and and and

Giraffa tippelskirchi tippelskirchi

Giraffa giraffa giraffa

Giraffa giraffa angolensis

The laryngeal flag is continuous with the auricular flag in certain perspectives ( and However, it is activated by the movements of foraging ( and and


A pedal flag occurs in two of the four species of giraffes. This consists of spotless pale surfaces on the feet and is activated by walking.

In Giraffa camelopardalis the pedal flag extends to the whole of the lower legs.

Giraffa camelopardalis rothschildi
second photo in

In Giraffa tippelskirchi the pedal flag is restricted to the pasterns and fetlocks (

Giraffa tippelskirchi tippelskirchi

An ilial flag and a pectoral flag occur only in Giraffa giraffa and are individually variable.


The ilial flag is a nebulously pale and sheeny area on the hindquarters, offset by a dark, anti-sheen effect on the rump above it. It can work in conjunction with the caudal flag (e.g. However, of all the flags it is - dependent on individual and illumination - the one most visible at a distance (e.g.

Giraffa giraffa giraffa
third photo in and


The pectoral flag is a paired pale patch on the anterior surface of the junction between forelegs and chest. It is most noticeable in mature males, which tend to be otherwise darkened.

Giraffa giraffa giraffa


No form of giraffe possesses all these flags. The distribution, by geographic area, is as follows:

  • species camelopardalis, found from West Africa to western Kenya, has an auricular flag (except in subspecies peralta) and a pedal flag (in attenuated form);
  • species reticulata, found in northern Kenya, has only an auricular flag;
  • species tippelskirchi, found from Kenya to eastern Zambia, has an auricular flag (perhaps relatively poorly developed), a laryngeal flag and a pedal flag (in accentuated form); and
  • species giraffa, found in southern Africa, has an auricular flag (perhaps relatively poorly developed), a laryngeal flag (relatively poorly developed), an ilial flag and a pectoral flag, the last two being restricted to subspecies giraffa.
Posted on March 31, 2021 02:25 AM by milewski milewski | 16 comments | Leave a comment