Does the greater kudu (Strepsiceros) possess an anterior auricular flag?

@magdastlucia

Everyone knows that the overall colouration of the greater kudu (Strepsiceros, https://www.inaturalist.org/taxa/42339-Tragelaphus-strepsiceros) is adapted for inconspicuousness.

The stripes and other markings tend to disrupt of the figure, particularly against a background of thorn scrub (https://www.inaturalist.org/observations/153426937).

Even the ear pinnae, which are remarkably large (https://www.inaturalist.org/observations/130293311), have a pattern intricate enough to contribute to this disruptive (camouflage) colouration (https://www.alamy.com/plains-game-on-the-african-plains-the-rare-roan-antelopes-greater-kudu-impalas-all-fair-game-for-the-predators-of-africa-image462891192.html?imageid=5EE28E15-6E74-4F9F-8C56-9D54B1F0BC5F&p=298851&pn=1&searchId=f89a4d97c4f3cea31551e30e7eb84de2&searchtype=0
and https://www.inaturalist.org/observations/122202839 and https://www.inaturalist.org/observations/159543578).

(Dear Reader, please bear in mind that the blush in the latter photo would probably not be visible to either the greater kudu or Carnivora, which are effectively 'red-green colour-blind'. Instead, these animals would see the ears in dark, pale, and 'shades of grey'.)

However, it is equally true that, in many views, the ear pinnae are conspicuous enough to draw attention to the figure (https://www.shutterstock.com/image-photo/female-greater-kudu-kruger-national-park-1072876346 and https://www.inaturalist.org/observations/155867431 and https://www.inaturalist.org/observations/161363460 and https://www.inaturalist.org/observations/146211806 and https://www.inaturalist.org/observations/143955834 and https://www.inaturalist.org/observations/137962439 and https://www.inaturalist.org/observations/103146864 and https://www.inaturalist.org/observations/63566582 and https://www.inaturalist.org/observations/53711503 and https://www.inaturalist.org/observations/368626).

Furthermore, the greater kudu seems not to have been recorded folding its ear pinnae out of sight in mild alarm, in the way known for a coexisting bovid that also has large ears, viz. the steenbok (Raphicerus campestris, https://www.inaturalist.org/observations/196285829 and scroll in https://www.africancraftsmarket.com/products/animal-skins/animal-skins-2/Steenbok-hide.html).

The potential conspicuousness of the ears in the greater kudu results partly from the size of the pinnae (https://www.istockphoto.com/photo/bus-service-a-female-of-kudu-taking-around-a-group-of-10-oxpeckers-gm871792544-145536069?phrase=antelope+legs&searchscope=image%2Cfilm).

This evolutionary enlargement reflects some adaptive combination of

  • acute hearing (mainly for vigilance),
  • thermoregulation (the bare skin on the front-of-ear becomes flushed with blood by means of dilation of the capillaries, in order to shed body heat), and
  • display (for communication, both intra- and interspecific).

My interpretation is as follows:

There is a preponderance of photos in which the ear pinnae show boldly, because this is the more photogenic option. Most observers, seeking a satisfactory photo, would hesitate to 'click the shutter' while the figure and its ears are hard to discern among the vegetational clutter.

When the figure is furtively active in relatively dense vegetation, it can 'freeze' the moment it detects the approach of a potential predator. Under these conditions, the front-of-ear can function congruently with the striping on the torso, to camouflage the figure.

If this succeeds, the predator overlooks the prey animal, and after a suitable pause the latter can resume quietly foraging.

However, if the individual concerned sees the predator begin to stalk, it can forestall this attempt by announcing itself in a way that clearly informs the predator that it has lost any advantage of surprise. The greater kudu can communicate this by moving a few paces into the sunlight, and standing attentively with the ears directed towards the threat.

This may perhaps be accompanied by gruff-barking in mild alarm (https://www.google.com/search?q=Audio+of+kudu+barking&sca_esv=596393425&sxsrf=AM9HkKkVdm9zDPj1trONw5hNvZoeGPzbdA%3A1704651678462&source=hp&ei=nuuaZdKOGsuVg8UP3oyogAs&iflsig=AO6bgOgAAAAAZZr5riFNgOQC3ak96SSAri5f5ov8WILy&ved=0ahUKEwjS1Yiu8suDAxXLyqACHV4GCrAQ4dUDCAw&uact=5&oq=Audio+of+kudu+barking&gs_lp=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&sclient=gws-wiz#fpstate=ive&vld=cid:790d618c,vid:yc3yldMnuKU,st:0 and https://www.facebook.com/watch/?v=2957306921206396 and https://www.google.com/search?q=Audio+of+kudu+barking&sca_esv=596393425&sxsrf=AM9HkKkVdm9zDPj1trONw5hNvZoeGPzbdA%3A1704651678462&source=hp&ei=nuuaZdKOGsuVg8UP3oyogAs&iflsig=AO6bgOgAAAAAZZr5riFNgOQC3ak96SSAri5f5ov8WILy&ved=0ahUKEwjS1Yiu8suDAxXLyqACHV4GCrAQ4dUDCAw&uact=5&oq=Audio+of+kudu+barking&gs_lp=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&sclient=gws-wiz#fpstate=ive&vld=cid:295d9cce,vid:IgVh-eVwI30,st:0).

In other words, I hypothesise that the pattern of colouration on the anterior surface of the ear pinna in the greater kudu has been adaptively configured in an ambivalent (versatile) way. The same pattern of dark and pale can function to hide the figure when held still and in shade or dappled shadow, or to advertise the figure - and its alert attentiveness - once concealment has proven futile and the better tactic is to step into the light and tell the predator 'I've seen you!'

An alternative framing invokes the difference between night and day.

Even if the pattern on the front-of-ear is bold enough that it tends to undermine camouflage in daylight, it is possible that in dim light it tends to function disruptively. This might be as important as the distinction between stationary and divulged by motion, because the greater kudu - unlike most bovids of its body size and more than the steenbok - is partly nocturnal.

On this basis, I would argue that the greater kudu qualifies as possessing an anterior auricular flag, but that this flag has been designed not to be mutually exclusive with camouflage-colouration.

Since inconspicuous (cryptic or disruptive = camouflage) colouration is the default assumption among ungulates, it is the bold aspect of the auricular pattern that deserves particular recognition.

In summary:
The greater kudu shows how the pattern on the front-of-ear can function as part of inconspicuous (disruptive) colouration before a potential predator detects the figure, and then as part of conspicuous colouration (anterior auricular flag) once 'freezing' is abandoned and the figure moves attentively in mild alarm, signalling to the intruder that it has been spotted.

Also please see https://www.inaturalist.org/posts/72489-display-of-the-tail-in-the-greater-kudu-is-puzzlingly-subtle-and-inconsistent#

Posted on 22 May, 2023 23:18 by milewski milewski

Comments

@beartracker @paradoxornithidae @variani18 @matthewinabinett @dejong

The following video footage is valuable in showing exactly how the tail of the greater kudu moves in visual accentuation of its alarm-vocalisation:
https://www.google.com/search?q=Audio+of+kudu+barking&sca_esv=596393425&sxsrf=AM9HkKkVdm9zDPj1trONw5hNvZoeGPzbdA%3A1704651678462&source=hp&ei=nuuaZdKOGsuVg8UP3oyogAs&iflsig=AO6bgOgAAAAAZZr5riFNgOQC3ak96SSAri5f5ov8WILy&ved=0ahUKEwjS1Yiu8suDAxXLyqACHV4GCrAQ4dUDCAw&uact=5&oq=Audio+of+kudu+barking&gs_lp=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&sclient=gws-wiz#fpstate=ive&vld=cid:790d618c,vid:yc3yldMnuKU,st:0.

With each utterance of a powerful version of the gruff-bark by an adult female individual in ostensible response to the proximity of Panthera pardus, the tail curls up, revealing the white pelage on the ventral surface of the tail.

This is done not by erecting the tail, but by holding it fairly low and activating its distal half.

Neither the upwards-curling nor the subsequent relaxation are particularly rapid (jerky). However, the flexing is more distinct than the relaxation, which is partial, and sometimes delayed.

The posture of the tail, at the moment of gruff-barking, is similar to that often adopted when the animal flees in mild alarm (https://www.inaturalist.org/posts/72489-display-of-the-tail-in-the-greater-kudu-is-puzzlingly-subtle-and-inconsistent#).

However, it is the intermittent movement of the tail while the animal stands/walks slowly, in synchrony with each vocalisation, that is noteworthy.

I have never seen this behaviour - a type of limited caudal flagging timed to provide some degree of visual accompaniment to a mainly auditory alarm-signal - mentioned in the literature.

Also see https://www.inaturalist.org/journal/milewski/72489-display-of-the-tail-in-the-greater-kudu-strepsiceros-is-puzzlingly-subtle-and-inconsistent#
https://www.facebook.com/watch/?v=831998774659275

Posted by milewski about 2 months ago

Add a Comment

Sign In or Sign Up to add comments