An unexpected convergence in colouration between giraffes and zebras

What do you notice about these two photos? and

Take it for granted that giraffes (Giraffa spp.) and zebras (four species of Equus) are similar: large ungulates with extreme colouration.

And that giraffes are by far the largest land animals with camouflage colouration, while zebras are so striped that the adaptive value of their colouration has been a major puzzle.

It seems safe to assume that, in both giraffes and zebras, the main functions of the overall colourations are to make the figures inconspicuous in some sense.

So, what in the above photos do I find remarkable?

Well, we have seen in previous posts about the moose (Alces alces) and various other ungulates, as well as various carnivores, that it is normal for largely inconspicuous animals to possess flags.

Flags are relatively small-scale patterns of colouration, subsumed within the overall colouration as long as the figure is stationary. However, they are large and dark/pale enough to become conspicuous once the animal moves in certain ways.

The intriguing convergence between giraffes (all species, both sexes, and both juveniles and adults) and zebras (albeit only one species, and only certain subspecies/individuals) is: both have unmarked, gleamingly pale ears, constituting auricular flags, when viewed from behind.

The auricular flags of giraffes and zebras are activated when the animals walk away intermittently. In this perspective there is a noticeable contrast between the whitish back-of-ear and the rest of the colouration, which is further accentuated by the normal movements of the ear pinnae. Such flagging presumably aids gregariousness because it makes it easy for individuals to keep track of each other's movements by means of the briefest glance. It also informs companions of any sudden attentiveness of an individual turning its eyes and ears towards something suspicious, thus promptly communicating any alarm.

The following, of Giraffa tippelskirchi tippelskirchi, shows how thoroughly camouflaged giraffes can seem by virtue of their colouration:

However, in all giraffes the back-of-ear is exempt from spotting: and

Furthermore, the short fur on the back-of-ear seems to possess a sheen, making it even more eye-catching in certain lights. The following show illuminations where this sheen effect is not apparent: and and

The following show how conspicuous the auricular flag of giraffes can be even at considerable distance: and and and and

Turning to zebras:

In three of the four species of zebras, the back-of-ear has complicated colouration:

Equus grevyi: and and and

(the following nicely compare the front- and back-of-ear of E. grevyi: vs

Equus hartmannae: and

Equus zebra: and

However, in several subspecies of the plains zebra (Equus quagga) there is a tendency for the back-of-ear to be mainly whitish (e.g. E. q. burchellii and

The basic pattern in this species, which varies according to subspecies and individual, is In several subspecies this can hardly qualify as an auricular flag because the whitish feature is too small.

However, in two northern subspecies (E. q. borensis and E. q. isabella) the whitish area covers most or all of the back-of-ear, and the ear pinna is unobstructed because the mane is particularly short ( and and and and and and and

In several other subspecies, there is individual variation:

Equus quagga burchellii and and and

Equus quagga chapmani and and and

Equus quagga boehmi and and and and and

The only extant subspecies in which I have yet to see any individual with an auricular flag is E. q. crawshayi ( and and

In the case of the extinct quagga (E. q. quagga) nobody has examined the museum specimens for this, but my impression from photos is that there was no auricular flag ( and If so, this is yet another way in which the extinct quagga was not merely an extrapolation of the trend in colouration from E. q. chapmani to E. q. burchellii.

Publicado por milewski milewski, 09 de septiembre de 2021


Instead of having an auricular flag, Equus grevyi seems to have a rump flag:

Publicado por milewski hace 4 meses (Marca)

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