Adaptive radiation of auricular flags in hippotragin bovids: Hippotragus, Oryx, and Addax, part 3

...continued from


Dear Readers, in order to refresh your search-image for posterior auricular flags, I offer the following of a reduncin bovid, Kobus defassa harnieri (

The above photo nicely illustrates how a given species/subspecies can have ear pinnae with conspicuois colouration, at moderate distances from the observer, on both the front- and back-of-ear.

Returning now to apply this search-image to hippotragins:

In most hippotragins, the back-of-ear has unremarkable colouration, as shown by the following:

Hippotragus equinus adult females:

Oryx dammah:

Oryx leucoryx:

Oryx beisa:

Addax nasomaculatus in summer pelage:

However, there are several exceptions, by

  • species,
  • sex, and
  • season.

Furthermore, posterior auricular flags in hippotragins result from

  • pigmentation/depigmentation, and/or
  • sheen effects, reflecting the structure of the hairs on the back-of-ear.

Species possibly qualifying for a posterior auricular flag (which may include the base of the ear pinna) are

An additional species, unlikely to qualify, but showing a suggestive pattern, is

  • Hippotragus niger.


The following show that the back-of-ear may possibly be pale enough, in adult males, to qualify for a posterior auricular flag ( and and and and

I have yet to see this pallor in adult or adolescent females ( and and and and and

Photos show evidence of sexual dimorphism in a (sheeny?) pallor on the back-of-ear in H. equinus, as follows:

This masculine auricular pallor is unusual among ungulates, and deserves further investigation. In particular:

For further information, please see comment below titled 'various views of the back-of-ear in the roan antelope'.


A case could possibly be made for a posterior auricular flag in adult males ( and mature females ( and second and third photos in

However, the back-of-ear is not consistently pale enough for this to be clear ( and

Differentiation of the back-of-ear by hue in H. niger does not qualify in the terms of this study, which heeds only darkness vs paleness ( and and and and

However, my disqualification of H. niger may warrant re-evaluation.

The clearest evidence I have found for a posterior auricular flag in H. niger is the following of a fully mature female individual, in which even the crown has turned dark:

The following - remarkably fortuitously - shows the anterior surface of the ear pinna in the same individual in the same illumination, for direct comparison:


Oryx gazella seems to qualify for a posterior auricular flag. However, this is so subtle that I scrolled through hundreds of photos before noticing it.

The pigmentation on the posterior surface of the ear pinna is similar to the ground-colour.

There is dark apical emphasis (, as on the front-of-ear. However, this is usually insufficient to make the back-of-ear conspicuous:

What I noticed after persistent investigation is that the back-of-ear sometimes appears conspicuously pale, accentuated by its apical darkness:
scroll in

This is owing to sheen, rather than depigmentation.

Furthermore, the sheen-effect is more consistent when the posterior surface of the ear pinna is viewed from the front:

The posterior auricular flag tends to be most noticeable when the animal faces the viewer, close-up, with the ear pinnae rotated. This suggests an emotional signal, probably in antagonistic interactions.

I hypothesise that, by human analogy, this facial expression communicates a message similar to that of a disapproving frown or an angry furrowing of the eyebrows (,closer%20together)%20%5B4%5D.).

A similar functional explanation may possibly apply to H. equinus, with the difference that it applies only in mature males in the latter species.


Addax nasomaculatus fails to qualify for either an anterior (see part 2) or a posterior auricular flag, in summer pelage.

However, it qualifies for a posterior auricular flag ( and and, in winter pelage.

The whole posterior surface of the ear pinna in A. nasomaculatus is conspicuous in winter pelage, because it is whitish in contrast with the ground-colour on neck, nape, and crown (

Also see:

Posted on 05 January, 2024 16:11 by milewski milewski


Posted by milewski 7 months ago

shows similarity to roan in flank-band near elbow

Posted by milewski 7 months ago


Posted by milewski 6 months ago

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