An interpretation of Ndumo Game Reserve, South Africa, part 2

...continued from https://www.inaturalist.org/journal/milewski/66630-an-interpretation-of-ndumo-game-reserve-south-africa-part-1#

Although the extermination of the yellow-billed oxpecker and the unnatural scarcity of the red-billed oxpecker (Buphagus erythrorhynchus, https://www.inaturalist.org/observations/108940322) in Ndumo Game Reserve were surely caused by the toxic cattle dips on nearby farms, the anthropogenic reasons for the scarcity of the Natal francolin are subtle.

Several species of francolins and spurfowl depend partly on elephant dung and on herbaceous plants (or the associated weeds) cultivated by the human species. With the removal of both the elephant and the human populations from Ndumo Game Reserve many decades ago, the habitat may no longer be suitable for phasianids other than the crested francolin (Dendroperdix sephaena), which continues to occur in small numbers.

My reasoning in the case of the Natal francolin would seem to apply also to the southern yellow-billed hornbill (Tockus leucomelas, https://www.inaturalist.org/taxa/5479-Tockus-leucomelas), which is likewise conspicuously rare in Ndumo Game Reserve today. [para needs revision according to info from Ken Tinley]

One effect of the unnatural scarcity of oxpeckers in Ndumo Game Reserve today is the pathological levels of infestation by ticks. Almost all adult individuals of the Cape giraffe (Giraffa giraffa) that I saw in Ndumo in 2013 carried patches of ticks on the back of the ear pinna, so dense that they formed a conspicuous dark patch against the otherwise pale fur. I have observed giraffes closely elsewhere but have never seen this phenomenon before. Some individuals of the common impala (Aepyceros melampus) were similarly afflicted in Ndumo.

Unlike the African bush elephant, the hook-lipped rhinoceros was reintroduced to Ndumo Game Reserve and, for a while, succeeded despite the scarcity of oxpeckers, its facilitators. Then this species declined for unknown reasons, well before its intense spate of persecution started in 2010. I explain the rise and fall of the hook-lipped rhinoceros in Ndumo Game Reserve according to a view of the anthropogenic history of the area.

When the human population of Ndumo was moved out of the reserve from 1924 onwards, a period of regeneration of the common pioneer plant species occurred. These pioneers took the form of acacias and the sickle-bush (Dichrostachys cinerea, https://www.inaturalist.org/observations/71153635), which are favourite foods of the hook-lipped rhinoceros (http://static1.squarespace.com/static/583eea74be659429d12fb2a8/583f290ae48aee953d4ed3fc/583f294fe48aee953d4ed6c1/1480534351176/articles-feeding-drinking.pdf?format=original).

In particular, horned thorn (Vachellia quadricornuta) temporarily dominated large areas of Ndumo Game Reserve before it grew to its mature size as a tree above the reach of the hook-lipped rhinoceros, and then senesced to be replaced by the typical components of Makatini Clay Thicket.

The hook-lipped rhinoceros rode what was actually a successional wave created by the removal of the human species – ourselves a fully native species throughout southern Africa. By 2006 only a few individuals of the hook-lipped rhinoceros remained in Ndumo despite the efforts of conservationists, and the last few have probably succumbed to illegal hunting.

My interpretation of the fate of the hook-lipped rhinoceros is ironic. Although humanity is currently its nemesis, prime habitat for this species may have, for thousands of years, been a product of the landscape mosaic created by alternating productive and abandoned farmlands.

A botanical symptom of the demise of the hook-lipped rhinoceros – which has probably emerged not once but twice during the history of this reserve – is the superabundance of the rhino thorn/grandthorn noors (Euphorbia grandicornis, https://www.inaturalist.org/taxa/337749-Euphorbia-grandicornis). This species has spines of convergent form with horned thorn and, despite its extreme defences, is accepted by the hook-lipped rhino as food. As a low-growing, spinescent form of succulent euphorbia, rhino thorn provides yet another link between Ndumo and the Eastern Cape - where a similar species, the green noors (Euphorbia caerulescens, https://www.inaturalist.org/taxa/577767-Euphorbia-caerulescens) is eaten by the hook-lipped rhinoceros.

My interpretation is that this euphorbia has recently been released from herbivory and will soon be untouched by any herbivore in Ndumo Game Reserve other than the Cape porcupine (Hystrix africaeaustralis, https://www.inaturalist.org/taxa/44173-Hystrix-africaeaustralis), which eats only the roots. Evidence of the Cape porcupine was so common during my visit in 2013 that I suspect that there has been a previously unnoticed increase in the population of this rodent in Ndumo Game Reserve since the decline of the hook-lipped rhinoceros. If so, a rare opportunity may have been missed to observe how the Cape porcupine interacts with the southern bushpig in terms of competition for food or, possibly, facilitation.

The blue wildebeest (Connochaetes taurinus taurinus), reintroduced to Ndumo Game Reserve in ?1994, is now common here. However, this was not necessarily the species of alcelaphin grazer originally present when Europeans first arrived. Alternative candidates are the tsessebe (Damaliscus lunatus) and – at the southernmost limit of its range – a tropical species, Lichtenstein’s hartebeest (Alcelaphus lichtensteini).

Had Ndumo Game Reserve been differently managed, it might have served as a special sanctuary for these species, which are relatively rare in South Africa compared with the blue wildebeest. The latter adds little value to the fauna of the reserve whether originally common or not. The tsessebe was reintroduced to Phongolo Nature Reserve, upstream on the same river system farther south in Zululand, but failed there. Does any reader know whether any attempt was made by the same authorities (the Natal Parks Board or the subsequent Ezemvelo KZN Wildlife) to reintroduce the tsessebe to Ndumo Game Reserve?

Perhaps the most puzzling faunal anomalies in Ndumo Game Reserve are the scarcity of the leopard and the absence of the chacma baboon [footnote on status of these species in Tembe Elephant Park]. Both species were persecuted by the indigenous people who originally farmed here, but who have been excluded from the reserve for more than half a century. Why have these species not recolonised the area and thrived?

Instead, the vervet monkey (Chlorocebus pygerythrus) is now common to the point of apparent superabundance - which in turn may have facilitated the competitiveness of the Livingstone’s suni (Neotragus livingstonianus) with the more common dwarf ruminant of the area, namely the Natal red duiker (Cephalophus natalensis). The Livingstone's suni, being the smallest of all ruminants in South Africa, may depend on fallen leaves, flowers, and fruits even more than the Natal red duiker does. It would be interesting to know whether the two species of dwarf ruminants originally - in the presence of both their predator the leopard and their facilitator the chacma baboon - coexisted as intimately in Ndumo Game Reserve as they do today.

Given the demand for spotted pelts in nearby Swaziland, it is easy to suspect that the leopard has been systematically trapped illegally in Ndumo Game Reserve for many years. Such corruption is flatly denied by local rangers even though they admit long-standing illegal hunting of ruminants for meat. I reason that if the reserve were infiltrated enough to exterminate the leopard it is inconceivable that the square-lipped rhino (Ceratotherium simum) would have been spared here as long as it has. Does any reader have an answer to the mystery of the scarcity of the leopard and the disappearance of the chacma baboon?

What is also interesting is that, in the absence of leopard, lion, and African hunting dog, there has apparently been no

• compensation by a rival carnivore, the spotted hyena (Crocuta crocuta), or
• release from the pressure of predation in the southern warthog (Phacochoerus africanus sundevallii) or the aardvark (Orycteropus afer).

One apparent superabundance that I noted in 2013, which might be explained by a lack of predators, was that of the Nile monitor (Varanus niloticus, https://www.inaturalist.org/observations/47112810 and https://www.inaturalist.org/observations/5134102).

I also found the old carcase of a mature individual of the southern African python (Python natalensis, https://www.inaturalist.org/taxa/111451-Python-natalensis), that had apparently been trampled to death, scattering many well-formed eggs for up to five metres. What was odd was that neither the body nor its eggs had been eaten, suggesting a lack of carnivores and possibly hinting that the largest snake in this fauna has also been released from pressure of predation.

I can summarise the distortions of the fauna in Ndumo Game Reserve according to my degree of puzzlement, as follows.

My least mysterious finding is the extreme scarcity of the southern bushbuck today, because the inadvertent experiment of boosting the numbers of the nyala has played out previously in various conservation areas in South Africa with this same result.

My most mysterious finding is the scarcity of the leopard, because this would seems to be the best-adapted carnivore for the area. Its near-extermination has not resulted in any apparent increase in other carnivores or in prey species such as the chacma baboon and the southern warthog.

Between these extremes lie the rest of the species mentioned above. The absence of the African bush elephant is no mystery but its effects on plants and other animals remain unsure. The different fortunes of, for example, the southern bushpig (superabundant) and the aardvark (puzzlingly scarce) remain unexplained by the nature of the vegetation or the apparent food-supply for these species.

Attempts to merge Ndumo Game Reserve with Tembe Elephant Park have failed for political reasons, the unprotected corridor between them being too useful for smuggling because it abuts the Mozambique border. There seems to be little prospect of the African bush elephant elephant returning to Ndumo, and now both species of rhinoceroses are doomed here too because they are worth so much more dead than alive. Although Ndumo Game Reserve is likely to retain the hippopotamus (Hippopotamus amphibius, https://www.inaturalist.org/observations/75693438), the balance between this species and the other megaherbivores will have been lost.

Posted on May 31, 2022 07:33 AM by milewski