Are there two species of oribi (Ourebia), instead of one?

Dear reader, can you spot the glaring error in the following picture of an oribi? (Scroll in https://www.wildlifeworldwide.com/locations/golden-gate-highlands-national-park.)

If your answer is not immediate, please see https://www.inaturalist.org/journal/milewski/69937-adaptive-colouration-in-the-oribi-southern-forms-are-more-conspicuous-than-northern-forms#.

The error is that the form of oribi (Ourebia) depicted for a national park in Free State province, South Africa, is completely the wrong form of oribi.

The real appearance of the oribi in Golden Gate National Park is this: https://www.inaturalist.org/observations/103241509.

Anyone familiar with the real oribi of South Africa should be able to spot, at first glance, that a photo from elsewhere in Africa has been carelessly inserted.

A search in Google Images quickly reveals that the photo (https://www.alamy.com/oribi-antelope-ethiopia-africa-wildlife-image335221666.html?imageid=6C385E16-3750-4D80-9C9B-C227349E09E3&p=836506&pn=1&searchId=d592d238c126347ec4d3725c2a7bbfc9&searchtype=0) was actually taken in central Ethiopia (https://en.wikipedia.org/wiki/Senkelle_Swayne%27s_Hartebeest_Sanctuary).

(Another website for a conservation area, depicting the wrong oribi in several photos, is http://www.kzn-southcoast.com/oribi-antelope.html.)

But there is more to this question of identity than meets the eye.

According to the current, rather neglected, taxonomy, the correction would be merely one of subspecies.

However, is it perhaps time to rethink the number of species in this genus, in the first place?

The patterns on the hindquarters are so different that it seems that there may actually be different species involved.

Let us provisionally call these two postulated spp. the common oribi and the southern oribi.

The scientific names would be:

• SOUTHERN ORIBI Ourebia ourebi (Zimmermann, 1783), vs
• COMMON ORIBI Ourebia montana (Cretzschmar, 1826).

These two spp. differ mainly in that, in the former alone, the tail is black and the buttocks are extensively white. This means that, in the southern oribi, the hindquarters are conspicuous at a distance, whereas in the common oribi the hindquarters are not conspicuous at a distance.

This would seem to make adaptive sense.

The southern oribi, after all, tends to live in extensively treeless grasslands, where opportunities to hide are limited. By contrast, the common oribi tends to live in savannas, where not only is the grass relatively tall, but there is some cover of shrubs and saplings.

Another obvious difference is in the ground-colour, covering most of the body. This is dull fawn in the common oribi, but bright fawn in the southern oribi.

However, there is a biogeographically intriguing complication.

This is that a form resembling the southern oribi, rather than the common oribi, occurs over a large area in the western half of Zambia, extending widely into Angola and narrowly across the Caprivi Strip of Namibia, into northern Botswana.

The subspecies name of this Zambian form, which has been photographed mainly in Kafue (https://www.alamy.com/stock-photo-oribi-ourebia-ourebi-kafue-national-park-zambia-11846014.html?imageid=B840C17C-6845-4AB0-9DA7-B971A6B338A4&p=74587&pn=1&searchId=45480e3d7233a9687b2df7a7f5357d3b&searchtype=0 and https://www.alamy.com/stock-photo-oribi-ourebia-ourebi-kafue-national-park-zambia-11846018.html?imageid=857A4ABE-7DBB-44E5-A844-B03268BAA80C&p=74587&pn=1&searchId=45480e3d7233a9687b2df7a7f5357d3b&searchtype=0) and Liuwa Plain national parks, is currently O. o. rutila.

This looks more similar to the southern oribi than to the form in Zimbabwe, Malawi, and Mozambique at similar tropical latitudes - which is currently called subspecies O. o. hastata.

So, if we were to recognise two spp. of oribi, then the adjective 'southern' might be subject to two caveats, viz.

• the distribution extends as far north as Katanga and north-central Angola, which are nearly equatorial, and
• this distribution is disjunct, the gap corresponding to eastern Botswana and western Zimbabwe (with the exception of Kazuma Pan National Park, https://en.wikipedia.org/wiki/Kazuma_Pan_National_Park, in the extreme northwest of Zimbabwe).

If true, what this would leave us with is a hitherto overlooked anomaly in the distribution of oribis in southern Africa.

This is that, when one crosses from the highlands of Limpopo province of South Africa (https://en.wikipedia.org/wiki/Limpopo) to the southeastern part of Zimbabwe, one changes the species of oribi. Yet when one moves all the way from Gauteng province of South Africa, across the easternmost Kalahari, to northern Botswana, one does not change the species.

For some strange reason, it seems that the following may be true.

The common oribi - which occurs widely from West Africa to Ethiopia and then through East Africa to central Mozambique - has penetrated as far south as low-lying southeastern Zimbabwe (https://www.ewt.org.za/wp-content/uploads/2019/02/18.-Oribi-Ourebia-ourebi_EN.pdf).

Here, the common oribi may perhaps survive in the Save Conservancy (https://savevalleyconservancy.org/), but seems never to have been photographed.

And this new perspective also raises the question of the real identity of any populations remaining in southern Mozambique.

These have previously been assumed to belong to ssp. ourebi, which seems reasonable given the former occurrence of this species (https://www.inaturalist.org/observations/235532) in the Lebombo mountains of northeastern Eswatini (https://en.wikipedia.org/wiki/Eswatini).

However, is it possible that the oribi occurring, or formerly occurring, in southern Mozambique, north and east of the Limpopo River (https://en.wikipedia.org/wiki/Limpopo_River#/media/File:Limpopo_River_basin_map.svg), is actually the common oribi, Ourebia montana hastata?

If so, this would mean that there are two species of oribi not only within the drainage of the Limpopo River, but also within the latitudes of Kruger National Park (https://en.wikipedia.org/wiki/Kruger_National_Park).

These would be

• the southernmost subspecies of the southern oribi, namely Ourebia ourebi ourebi (https://www.inaturalist.org/observations/98375681), in Limpopo province, Mpumalanga province, and Eswatini, and
• the southernmost subspecies of the common oribi, namely Ourebia montana hastata (https://www.inaturalist.org/observations/51195346), in southeastern Zimbabwe and southern Mozambique.

Publicado el septiembre 15, 2022 01:12 TARDE por milewski