My own foraging records for herbivores during drought in Kruger National Park, September 2016

I visited Kruger National Park for two weeks in September 2016, in drought conditions (https://www.theguardian.com/world/2016/sep/14/south-african-national-park-kill-animals-severe-drought and https://www.tripadvisor.com/ShowTopic-g312618-i9872-k9610530-2016_drought-Kruger_National_Park.html and https://www.tandfonline.com/doi/abs/10.2989/10220119.2020.1718755 and https://www.usatoday.com/story/news/world/2016/09/14/south-african-park-kills-350-hippos-buffalos-amid-drought/90345860/ and https://blog.rhinoafrica.com/2016/10/27/natural-cycle-kruger-drought/).

I took the opportunity to collect foraging observations on various large mammals, as we drove along. Although incidental, these amount to some noteworthy findings, which I shall summarise here.
 
Each foraging record consists of one individual of one species, eating one species of plant on one occasion.
 
African bush elephant (Loxodonta africana):
 
I collected 22 or more records for this species, during this visit. The individuals observed were mainly juvenile/adolescent males, but I observed at least 5 records for females too, including both adults and juveniles/adolescents. Almost half of the records were on Colophospermum mopane, the rest being on Senegalia nigrescens, Philenoptera violacea, Phragmites mauritianus, and (with only one record each) Combretum sp. indet., Dichrostachys cinerea, Euclea ?divinorum, Vachellia tortilis, and an unidentified woody species. At least 7 records were for leaves. The rest being for thin bare stems, except for one noteworthy record for root-bark. In the case of mopane, most (70%) of the records were for coppice stems (which were bare or actually bared by the elephant by means of stripping and discarding the remaining reddish leaves). The stems eaten belonged to not only mopane but also woody legumes (Senegalia, Vachellia and Dichrostachys). Foraging was destructive in the case of P. violacea and Senegalia nigrescens, but not Vachellia tortilis. In the case of Phragmites I did not see the parts eaten, and I assume that both leaves and stems were included. It is noteworthy that one individual took the trouble to push over a whole tree of S. nigrescens just to eat the root-bark, which it stripped laboriously, leaving the rest behind. There was no clear pattern w.r.t. deciduousness, partly because these records include both astringent evergreens (e.g. Euclea) and typical drought-deciduous woody plants (e.g. Senegalia nigrescens), and partly because the food-plants do not conform well to this distinction in the first place. By far the most important/outstanding finding, in all of this, was the apparent treatment by the elephant in Kruger National Park of coppice mopane as a staple at this dry time, systematically selecting less-than-pencil-thin stems near ground level and laboriously struggling to break off these obviously extremely fibrous stems, one by one and with no leaves as part of the reward.  The pattern suggests coevolution between mopane and elephant, which shapes the vegetation as the African Bush elephant repeatedly breaks the coppice stems and maintains mopane in its suppressed, shrubby form over large areas. The megaherbivore also shapes another woody legume, P. violacea, in an extremely noticeable way, and it was gratifying actually to observe the animal inflicting this wholesale damage. As for S. nigrescens: I have been aware, since hiking in the Malelane Mountain Bushveld, of the tendency for the African Bush elephant to push over trees of this species. However, it was illuminating to observe that this can be done not only as a long-term ‘farming’ of the foliage, but also for the immediate reward of ?trace element-rich root-bark. During this visit I noticed that, for some reason, the African Bush elephant does not disfigure Combretum imberbe even at its vulnerable-looking sapling stage. Why not? In this way, there is some similarity/analogy between C. imberbe and V. tortilis. Both were still in leaf during this drought, but neither was disfigured. This is an apparent case of conservation by the megaherbivore, because this sparing cannot be explained by the sheer size of the plants (or even the hardness of the wood in the case of C. imberbe).
 
Impala (Aepyceros melampus):
 
I obtained approximately 40 records, the number not being precise because of the herding of this species. Of course, the impala was probably also laboriously browsing the thin pickings left on preferred plants such as acacias. However, I did not obtain any actual records, just circumstantial evidence, of this. Most of the records were for litter, but there were was also one clear record for green lawn of Cynodon dactylon, and at least one other circumstantial record of a similar kind on a still-green riverbed. Although only about 12% of the records were for browsing Colophospermum mopane directly, this behaviour is noteworthy. The plants foraged as litter were a) phenologically anomalous individuals or taxa, from which the chacma baboon knocked down fresh material (e.g. Kigelia, Sclerocarya) and b) a tardily deciduous species (Berchemia discolor) shedding leaves, with a part played by the chacma baboon . The total number of plant species in these records is 7; the total % of the records referring to litter is >50%. During this dry time there were few foraging opportunities for the impala w.r.t. grazing (because this species accepts grass only in the green condition) and direct browsing (because so little palatable foliage remained within reach). The exceptions were Cynodon dactylon near a dam, and scattered Flueggea virosa on a basalt plain with largely treeless vegetation. As a result, the impala largely resorted to litter and mopane, the two categories overlapping because some of the mopane leaves were taken in the form of green litter. Much of the litter was inadvertently facilitated by the chacma baboon, as exemplified by an anomalous individual of Sclerocarya birrea. Many individuals of the baboon were feverishly consuming the shoots and discarding what looked like mainly the petioles, to the benefit of several individuals of the impala below the tree. I saw circumstantial evidence that the impala sometimes creates a browse-line on mopane, despite it being unlikely that the impala eats mopane as anything other than a non-preferred, dry-season ‘fallback’.
 
Greater kudu (Strepsiceros strepsiceros zambesiensis):
 
I obtained 17 records, all for direct browsing. The plants were mainly combretums of various species (9 of the 17 records), but also sometimes mopane. Euclea and Capparis tomentosa seemed to be ‘last resorts’, the former because it is so tannin-rich as to be unpalatable, and the latter partly because it is so prickly. It is significant that there is no browse-line on the evergreen Capparis tomentosa. I also observed, circumstantially, a distinct browse-line on Trichilia emetica, that seemed to correspond to the height of the kudu. Overall, these results are largely as expected.
 
Southern giraffe (Giraffa giraffa giraffa):
 
I obtained 5 records. The browse-line on Trichilia emetica at about kudu-height implies that this evergreen tree is not attractive to the giraffe for some reason. The most noteworthy result here was another negative one: in two weeks of looking, I never once observed the southern giraffe browsing mopane. The record of a mature male individual laboriously attempting to strip tall Salix, at about its maximum reach, is noteworthy because a) this is not a typical African plant, b) Salix was anomalously in shoot during this drought, and c) the main problem for giraffes here was the uprightness and springiness of the stems. This which make the stems hard to grasp in the giraffe’s mouth, despite the superficial impression of defenceless in Salix owing to a lack of spines or dense branchwork. I had the impression that, in the vast mopane lands of the northern Kruger National Park, a staple of the southern giraffe was sapling Combretum imberbe, the animals commuting hundreds of metres from one individual sapling to another among the dominant mopane. The acceptance of Capparis tomentosa, which is obviously not a favourite but is accepted to some extent in the dry season, is similar to what I observed for the greater kudu. For both giraffe and kudu, C. tomentosa seems to be a non-preferred food because of a) prickles and b) unpalatability owing to some unknown chemical defence. In summary, I obtained few records for the southern giraffe, but these revealed some aspects new to me.

Posted on July 7, 2022 05:26 AM by milewski