Puzzles about the geographical distribution of the bush duiker

The bush duiker (Sylvicapra grimmia) is the most widespread and altitude-tolerant species of wild ungulate in Africa, but its distribution and habitat are inconsistent and unpredictable in certain ways. Here are the most important questions.

Firstly, why has the species not occurred in Mediterranean North Africa, and which species - if any - has replaced it ecologically, there?

The nominate subspecies grimmia (see https://www.inaturalist.org/observations/64169127) is common in various vegetation types in the mediterranean-type climate of South Africa, suggesting that the species should also occur in the similar climate of rainy winters and dry summers in the other hemisphere. Yet the genus Sylvicapra seems absent even in the fossil record in North Africa.

Secondly, why does subspecies pallidior (see https://www.inaturalist.org/observations/42383809), adapted to the Sahel of the Sudan and Chad, not extend farther west? And why does the similar, but disjunct, subspecies coronata (see https://www.facebook.com/Niokolo.Koba.Expedition/photos/a.1520863891514532/1675677672699819/), occur only in extreme western West Africa?

Put together, the puzzle is: why is the bush duiker absent from the Sahel all the way between Senegal and Chad?

Thirdly, why is the bush duiker absent from most of the Horn of Africa (from Eritrea through Djibouti and Somaliland to Somalia and eastern Kenya), given that it is widespread in similarly dry climates in southern Africa (subspecies steinhardti) and the eastern Sahel?

Fourthly, why is it that, to this day, not one photo of the bush duiker has been published from the whole Serengeti Ecosystem, including Ngorongoro Conservation Area and the Maasai Mara National Reserve? The subspecies here is nyansae, which is arguably synonymous with hindei, the subspecies of the Kenyan highlands east of the Great African Rift.

And why are there so few photos of the bush duiker - apart from freshly-dead trophies posted on the websites of the hunting industry - from elsewhere in Tanzania, where the subspecies is orbicularis? In contrast to the extreme frequency of photos from e.g. Kruger National Park in South Africa (where the subspecies is caffra), I have yet to see any photo of this species from Manyara, Ruaha, Saadani, Mkomazi, Rukwa, Selous, and other reserves in Tanzania.

Indeed, there is a puzzling overall scarcity of photos of orbicularis (an exception is https://www.inaturalist.org/observations/4988736), despite its wide distribution from the lower Zambesi River across most of Mozambique and Tanzania to eastern Kenya (where there is also a lack of photos in the Tsavo national parks).

Posted by milewski milewski, August 23, 2020 21:08

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If you are looking for photos from the serengeti the Serengeti Lion Project operates a grid of 225 trail cameras in the Serengeti National Park. In the 7.18M images captured between 2010 and 2016 volunteers on the Snapshot Serengeti project identified 114 animals as common duiker, however less than a quarter are clearly duiker most are other misidentified antelope. The similar (smaller?) camera trap grid in Grumeti ~50km NW has also capture duiker photos but unfortunately the data has not been made available.

More details: https://www.nature.com/articles/sdata201526

Posted by lwnrngr over 2 years ago (Flag)
Posted by milewski about 1 year ago (Flag)

What seems to happen is that the niche of Sylvicapra is partly usurped, in the equatorial zone from Tanzania to the Horn of Africa, by Madoqua. This leaves Sylvicapra common only at altitudes too high for Madoqua (e.g. in Aberdares National Park) and, at lower altitudes, too close to human settlement for Madoqua.

Posted by milewski about 1 year ago (Flag)

I have certainly never seen them in either Tsavo East or West. If I do, I'll certainly do my best to get a photo! Based on their habitat preference elsewhere in Kenya, I wouldn't expect them to be numerous or common in either Tsavo NP, but possibly present in low numbers in some of the forest patches in Tsavo West and maybe up on the Chyulu Hills

Posted by zarek about 1 year ago (Flag)

@zarek Many thanks again for adding this valuable information.

Posted by milewski about 1 year ago (Flag)

The Sylvicapra grimmia is highly varied, I tried searching for data on it's population estimates, apparently there's an unpublished (or published) study showing the population of Sylvicapra grimmia is possibly near, or above the range of 10 million individuals. This information was sourced from wikipedia, in the article 'List of even-toed ungulates by population', where it conjectures, Sylvicapra grimmia, population : 1 660 000, Considered extremely conservative; yet-to-be-published research shows it may number as high as 10000000.

Posted by paradoxornithidae 4 months ago (Flag)

I suggest the three following keys to understanding the ecology of Sylvicapra grimmia.

Firstly, it is one of the more generalised species of African ungulates, in diet. For this reason, it tends to be excluded by specialists. This may help to explain its absence from most of the Horn of Africa, where Madoqua spp. plus gazelles are superior competitors owing to the bimodal rainfall and associated reliability of plant growth in these tropical semi-deserts. It is possible that exclusion in the Sahel has been owing partly to long-standing abundance of the domestic goat (Capra hircus).

Secondly, whereas other cephalophins have rainforest affinities, Sylvicapra has high-altitude affinities. This may help to explain why it is the only small bovid to occur in the moorlands on the high mountains in Kenya and Tanzania.

Thirdly, S. grimmia is perhaps the most commensal of all ruminants in Africa. This is easily overlooked in southern Africa, where it occurs both in the wild and close to human settlement. However, in East Africa this becomes crucial. Because the habitat of S. grimmia tends to usurped by Madoqua and gazelles here, it is only close to human settlement that S. grimmia remains - as the sole wild ungulate, adapted to cope with snaring and attacks by the domestic dog.

(The adaptive profile, I suggest, consists of a combination of facultatively nocturnal activity, braininess exceeding that of antilopins, endurance in running despite a body-conformation more typical of cover-dependent ruminants, and maximum frequency of reproduction short of any modification of monotocy.)

In Kenya, to find S. grimmia, one must go either to a mountain or to a village/horticultural area. The species is essentially excluded from the national parks and game reserves by competing, more specialised bovids.

Posted by milewski 4 months ago (Flag)

Quite interesting that it faces such intensive competition to the point of seeking out areas near human habitation.

Posted by paradoxornithidae 4 months ago (Flag)

Thanks for the information, it didn't come to my mind to ever think of the affinity of Bush duiker to non protected areas (it applies near-exclusively to Eastern Africa, if I'm not mistakened.)

Posted by paradoxornithidae 4 months ago (Flag)

I think S. grimmia tends to be commensal throughout its range. I do not think of this in terms of the species having been driven, in any real sense, to this habitat by competitors. Instead, as I see it, there is a niche for a commensal, provided that this animal can cope with the collateral risks (mainly snares and the domestic dog). Other small ruminants would also exploit horticultural affluence if they could survive the associated pressures. In southern Africa, S. grimmia survives in horticulture by virtue of its anti-predator competence, and it survives in the wild by virtue of its dietary versatility (generalism). In East Africa the former remains, but the latter fails. I suppose that what this adds up to is that S. grimmia can be characterised as a trophic generalist but an anti-predation specialist, overall?

Posted by milewski 4 months ago (Flag)

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