The puzzle of conspicuous pallor in a Sahelian giraffe, part 1

Does anyone doubt that, in general, the colouration of giraffes is a form of camouflage?

The flags which I have described (see https://www.inaturalist.org/journal/milewski/48447-conspicuous-features-of-colouration-in-giraffes#) hardly negate this generalisation, because they are subsidiary features.

However, one subspecies of giraffe has overall colouration so conspicuously pale that it does seem to mean a partial negation (https://africa.cgtn.com/2018/11/22/niger-to-move-protected-giraffes-as-habitat-shrinks/ and https://www.dreamstime.com/stock-photo-salivating-giraffe-its-dripping-saliva-epic-image70986808).

I refer to Giraffa camelopardalis peralta (https://en.wikipedia.org/wiki/West_African_giraffe and https://www.researchgate.net/profile/Bertrand-Chardonnet/publication/296408231_Antelope_Survey_Update_n9_November_2004_IUCN_SCC_Antelope_Specialist_Group_Report_Special_Issue_West_and_Central_Africa/links/56d5466608ae2cd682b9a145/Antelope-Survey-Update-n9-November-2004-IUCN-SCC-Antelope-Specialist-Group-Report-Special-Issue-West-and-Central-Africa.pdf#page=36 and http://travel2unlimited.com/niger-koure-giraffes/) of the western Sahel.

The particular pallor of Giraffa camelopardalis peralta is owing mainly to the breadth of the whitish 'matrix' among the blotches (see https://www.inaturalist.org/observations/91931958 and https://www.inaturalist.org/observations/67258492).

This differs from any pale overall effect in the form of giraffe inhabiting the edge of the Namib desert in southern Africa, which is owing mainly to fading of the blotches themselves and does not particularly affect the head or legs (Giraffa giraffa angolensis, see https://app.nimia.com/fpvideo/746972087/746972087-giraffe-walking-namibia and https://giraffeconservation.org/programmes/nw-namibia/).

The following photos of the most pallid individuals show how the camouflage effect has been compromised in Giraffa camelopardalis peralta in its current habitat. Although a corollary of the pallor is that the auricular and pedal flags are reduced, the caudal flag is if anything enhanced, because the tail-tassel remains black in all individuals.

https://www.inaturalist.org/observations/89357382
https://www.inaturalist.org/observations/66647598
https://www.inaturalist.org/observations/66511242
https://www.inaturalist.org/observations/66511269
https://www.inaturalist.org/observations/91633228
https://www.inaturalist.org/observations/84033823
https://www.inaturalist.org/observations/66511261
https://www.inaturalist.org/observations/66510605
https://www.inaturalist.org/observations/66510563
https://www.bornfree.org.uk/articles/conservation-update-gcf

Can it not be said that G. c. peralta has, in evolutionary terms, switched from inconspicuous colouration to conspicuous colouration? The mechanism has been a quantitative shift (mainly an encroachment of the pale matrix relative to the blotching), but the effect seems qualitative.

If so, this seems convergent with the conspicuous pallor of three other gregarious ruminants of the southern fringes of the Sahara, as exemplified by the following views of Oryx dammah:

https://www.shutterstock.com/nb/image-photo/herd-scimitar-horned-oryx-dammah-walking-1114267055 and https://www.shutterstock.com/nb/image-photo/herd-scimitar-horned-oryx-dammah-walking-1114267097.

Oryx dammah (https://www.inaturalist.org/observations/80301962), Addax nasomaculatus and Nanger dama ruficollis (https://www.hatadaranch.com/dama) all inhabited the vicinity of the Sahara, with O. dammah coexisting in the Sahel with giraffes (including G. c. peralta), A. nasomaculatus penetrating the Sahara itself, and N. d. ruficollis living in the eastern Sahel (where the local form of giraffe was not as pallid). In converging on a pattern of conspicuous overall pallor, these species set an unique pattern among the arid-adapted ungulates of the world.

I realise that:

  • arid-adapted reptiles, birds, and small mammals tend to be pallid as a form of crypsis in the pale environments of deserts, particularly sandy deserts;
  • there is seasonal variation in the colouration of A. nasomaculatus and possibly also the other two bovids referred to here; and
  • hippotragins and gazelles tend to be adaptively conspicuous even in savannas, which can be partly explained by the futility of trying to hide as gregarious animals in the open.

However, ruminants in the southern African deserts and semi-deserts (https://www.istockphoto.com/photo/gemsbok-oryx-in-namib-desert-gm146923746-14197980 and https://www.agefotostock.com/age/en/details-photo/springbok-antidorcas-marsupialis-adults-walking-on-sand-namib-desert-in-namibia/YS1-1722745) lack the relevant pattern of colouration. In the degree of their pallor, our three bovids seem to have adapted in convergent ways to the particular conditions of the Sahara and its southern edges.

Seen in this context, does the pallor of G. c. peralta not seem to be part of a regional faunistic pattern?

The following illustrate the pallor of our three bovids, and the adaptive convergence that this represents.

Oryx dammah:
https://www.shutterstock.com/nb/image-photo/huge-herd-scimitarhorned-oryx-sahara-wildlife-1988644823
https://www.shutterstock.com/nb/image-photo/herd-scimitar-horned-oryx-dammah-walking-1114267079
https://www.inaturalist.org/observations/74899599
https://www.shutterstock.com/nb/image-photo/antelope-scimitar-horn-oryx-leucoryx-due-1605546127 https://www.shutterstock.com/nb/image-photo/antelope-scimitar-horn-oryx-leucoryx-due-1606769167 https://www.shutterstock.com/nb/image-photo/scimitar-oryx-aka-sahara-endangered-animal-1093058519 https://www.shutterstock.com/nb/image-photo/very-rare-scimitarhorned-oryx-dammah-extinct-1932362348
https://www.shutterstock.com/nb/image-photo/scimitar-oryx-aka-sahara-endangered-animal-1093058531
https://www.shutterstock.com/nb/image-photo/scimitar-oryx-aka-sahara-endangered-animal-1219348936
https://wildlifeconservation101.files.wordpress.com/2012/04/images-2.jpeg

Addax nasomaculatus:
https://www.dreamstime.com/stock-photo-beautiful-addax-desert-eilat-image72805856
https://www.dreamstime.com/addax-walking-jebil-national-park-tunisia-image126127489
https://creatures-of-the-world.fandom.com/wiki/Addax?file=Adult_addax.jpg https://pixabay.com/photos/addax-negev-desert-desert-dweller-4764789/
https://www.istockphoto.com/photo/a-critically-endangered-addax-also-known-as-the-screwhorn-or-white-antelope-stops-to-gm1141454086-305811175
https://www.dreamstime.com/royalty-free-stock-photos-antelope-addax-image19237788

Nanger dama:
https://naturerules1.fandom.com/wiki/Dama_Gazelle?file=3e2b7d460fe86e7d50d1bfec49723c12.jpg
https://www.iucn.org/ssc-groups/mammals/mammals-a-e/antelope/resources http://lh3.ggpht.com/_1wtadqGaaPs/TCiTe14fKOI/AAAAAAAAGm4/SeKuL3yo1c4/s1600-h/tmp1127_thumb4.jpg
https://www.texasdivide.com/dama-gazelle

to be continued...

Posted by milewski milewski, November 18, 2021 11:28

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