The Common Warthog and the Desert Warthog

[AFRICAN INDABA]

The Common Warthog and the Desert Warthog
by Peter Grubb

Extracted from ?strong>Pigs, Peccaries and Hippos Status Survey and Action Plan (1993)?br>

The warthogs differ in proportions from the other Afrotropical suids. The lower tusks do not wear down the tips of the upper tusks, which are long and curved. The tusks of sows are relatively large in proportion to those of boars. The pelage is coarse and very sparse, except for a prominent dorsal crest of long bristles. In young animals especially there is often a fringe of white hairs on the cheeks. Both genal and rostral warts are present, the latter unsupported by bony excrescences.

1. Common Warthog (Phacochoerus africanus)
This species is very widespread, occurring in all nations, which extend into the Northern Savanna or the Southern Savanna and the bordering arid zones. The following names would be available if subspecies were to be recognized: africanus (Senegal), fossor (Chad), bufo (Sudan), aeliani (Eritrea), centralis (eastern Zaire), massaicus (Tanzania), sundevallii (Natal) and shortridgei (Namibia). Systematic studies of the common warthog have been based almost entirely on skulls, as the sparsely-haired skins are rarely preserved and almost nothing is known about variation of the pelage. There is much variation in the form of the skull but very few biologists have studied warthog skulls to determine geographic variation in the species. Preliminary analysis of skull measurements indicates the following. West African skulls are very large. Specimens from the Sahel are smaller and may grade into the Eritrean population. Central African populations also have very large skulls. Kenya specimens are similar but smaller, and Southern African warthogs are smaller still. Samples from the following areas are sufficiently differentiated in at least one measurement to be regarded as subspecifically distinct: Senegal/Eritrea; Senegal/Kenya; Kenya/Eritrea; Eritrea/ Somalia; Natal/Malawi; Natal/Senegal. But relatively substantial samples from Zambia, Katanga, Kivu-Rutshuru and Kenya cannot be separated from each other or from Malawi or Natal.

Subspecies bufo and centralis are certainly redundant and synonyms of massaicus; shortridgei is almost certainly a synonym of sundevallii. Peripherally distributed africanus, aeliani and sundevallii are distinct from each other, but they appear to link up - perhaps clinally - with other supposed subspecies. It may prove necessary to regard this taxon as monotypic, exhibiting geographic variation of such a continuous nature that discrete subspecies cannot be identified. In the meantime, the following (four) subspecies may be recognized provisionally:

a) Northern Warthog, Phacochoerus africanus africanus
Range: Northern Savanna and Sahel region (including: Mauritania, Senegal, Guinea Bissau, Ivory Coast, Burkina Faso, Nigeria, Chad, Sudan, CAR, N. Zaire and S. Ethiopia).

b) Eritrean Warthog, Phacochoerus africanus aeliani
Range: Eritrea, Djibouti and Somalia only?

c) Central African Warthog, Phacochoerus africanus massaicus (synonyms: bufo, centralis and (?)fossor)
Range: East and Central Africa (including: Kenya, Zaire, Rwanda, Burundi, Katanga, Zambia, Malawi and Angola).

d) Southern Warthog, Phacochoerus africanus sundevallii (synonym: shortridgei)
Range: Southern Africa (including: Zimbabwe, Botswana, Namibia, Natal).

2. Cape and Somali Warthogs (Phacochoerus aethiopicus)
Two species of warthog have been recognized. The Cape warthog was distinguished principally by its lack of functional incisors. The natural distribution of the Cape warthog was never properly identified and few specimens ever became available, none after the mid-nineteenth century. The specific name of the Cape warthog is the earliest one of the genus, so when all warthogs were considered to be one species, the characteristics of the better-known common warthog became associated with the name of the less well-known species. It became the accepted view among zoologists that the Cape warthog was no more than an extinct geographic representative of the common warthog. Paleontologists on the other hand have recognized two kinds of warthog in fossil material from South Africa and have treated P. aethiopicus and P. africanus as two different species, believing that the former is now extinct.

In 1909, L?nberg noted that two male warthog skulls obtained in Somalia also lacked incisors. He created a new species, P. delamerei, on the basis of these specimens and noted other similarities with P. aethiopicus, though he was not convinced that these two taxa were immediately related to each other. Nevertheless, warthogs with a specialized incisor-less morphology and other characters were now known from South Africa and East Africa. Roosevelt & Heller (1922) noticed this discontinuous distribution between north-east and south Africa - between Somali Arid and Southwest Arid Zones. In the interim, however, Lydekker (1915) had grouped all warthogs into one species, P. aethiopicus - the specific name properly associated with the Cape warthog. There appear to be no acknowledgements in the literature of Roosevelt & Heller's (1922) perceptive observations nor of the anatomical features linking delamerei and aethiopicus.

My own studies not only confirm differences between the common warthog and the Cape species, but that the Somali warthog and the Cape warthog are so alike that they should be regarded as conspecific. The principle features of the Cape/Somali warthog, P. aethiopicus, in comparison to the common warthog, P. africanus, are:

- the skull is relatively small, but proportionately shorter and broader;

- the front part of the zygomatic arch is thickened by internal sinuses and swollen into a spherical hollow knob just in front of the jugal-squamosal suture (in the common warthog, the zygomatic arch may be robust but it is never quite so thickened and there is no formation of a knob);

- there is never any trace of upper incisors, even in relatively young individuals, and the lower incisors, even if present, are rudimentary and non-functional (whereas the common warthog always has two upper incisors, though these may be lost in very old animals, and usually six, functional lower incisors in the adult dentition, of normal suine form);

- in the Cape warthog (but not yet confirmed in the Somali form), the large third molars are very different from those of the common species in that no roots have been formed by the time all the enamel columns have come into wear, so that the columns are able to continue growing and extend the life of the tooth; and

- in the common warthog the skull roof behind the internal nares is marked by two deep and distinct 'sphenoidal pits', not found in any other African suid, while in the Cape/Somali species, these pits have expanded enormously, disappearing as distinct entities, so as to contribute to two vaults between the pterygoids, separated by a deep vomerine ridge.

One could not have better morphological evidence for the existence of two species. Furthermore they may even be sympatric in some places. The two subspecies of desert warthogs may be described as follows:

a) Cape Warthog, Phacochoerus aethiopicus aethiopicus (extinct)

Cape warthog specimens in museums lack locality records but specimens subsequently identified as belonging to this species were obtained by Sparrman between the Sondags and Boesmans rivers, eastern Cape Province, and by Burchell on the upper Orange River, south of Hopetown, again in the eastern Cape. The full extent of the Cape warthog's former distribution remains unknown. Possibly it was restricted to the Karoo. There is no mention of this subspecies being obtained after about 1860.

b) Somali or Desert Warthog, Phacochoerus aethiopicus delamerei

This geographic representative of the Cape warthog is recorded from Somalia, both in the north and in Jubaland in the south, and from northern Kenya. Both this species and the common Warthog have been obtained in northern Somalia, where locality records for the common species form an enclave in the vicinity of Berbera, with sparse records of Somali warthog to the west, east and south.

The two species may be parapatric or even partly sympatric and ecologically segregated in northern Somalia, but this has yet to be confirmed. Their relative geographical disposition in Kenya (or eastern Ethiopia) cannot be assessed at all in the absence of adequate specimens or information. Somali warthog from Kenya and Jubaland are larger than those from northern Somalia and it may be necessary to describe them as a separate subspecies. Not enough specimens are available, however, to determine whether this should be done.


Warthogs In Africa
by Randi, E., D辿uart, J.-P., Lucchini, V. and Awan, R. (Mammalian Biology 67 (2002) 91-96
Abstract

Evidence Of Two Genetically Deeply Divergent Species Of Warthog In East Africa

Two species of warthogs (Phacocherus) differing by the number of functional incisors were described in the Holocene fossil record; the common warthog (P. africanus) widespread in sub-Saharan Africa and the Cape or desert warthog (P. aethiopicus) which was considered extinct since 1896, but was recently rediscovered in East Africa by morphological analyses. Mitochondrial and single-copy nuclear DNA sequences show that common and desert warthogs belong to two deeply divergent monophyletic lineages, that might have originated in the last part of the Pliocene. The finding of two divergent extant species of warthogs highlights the importance of molecular methods applied to the knowledge and conservation of biodiversity in Africa to uncover the tempo and mode of its species evolution.


Distribution Of The Common Warthog And The Desert Warthog In The Horn Of Africa
by D辿uart, J. P. and Grubb, P. , East African Wild Life Society Afr. J. Ecol. 39, 2001, 156-169
Abstract

The Somali warthog (Phacocherus aethiopicus delameri) is the surviving relative of the Cape warthog (P. a. aethiopicus) which formerly inhabited Cape Province but became extinct in the last century. It is only recently that these two subspecies of Phacocherus aethiopicus have been restored to the status of a species the desert warthog distinct from the common warthog P. africanus. Mitochondrial DNA analysis has recently confirmed that the common and desert warthogs are two different and widely divergent species. This preliminary study maps their distribution in the Horn of Africa and discusses the significance of ecological barriers that limit these distributions. 133 skulls from 64 different localities in 5 countries åœostly from museum collections were identified. New material was obtained from the field and reliable literature data were also recorded. Locality records suggest the optimal habitats of desert warthog are low altitude arid lands. The two species may overlap locally in northern Somalia, northern and eastern Kenya and southern and sout-eastern Ethiopia, but the desert warthog's precise range is still not accurately established and basic data about its conservation status, ecology and behavior are still very poor.


A Photographic Guide To The Differences Between The Common Warthog And The Desert Warthog
by D辿uart, P.-J. and Grubb, P. , Suiform Soundings, Volume 5, no. 2. December 2005

Introduction
The IUCN/SSC Pigs, Peccaries and Hippos Conservation Action Plan stressed the important gaps in our knowledge of Phacochoerus aethiopicus after the revelation of the existence of a 鉄omali Warthog? Ph. aethiopicus delamerei, a living representative of the Cape warthog, a taxon thought to be extinct since 1860. The Plan recommended a number of priorities for conservation action and for research, in view of clarifying the systematic and ecological relationships between P. aethiopicus and P. africanus. These recommendations included an assessment of their conservation status, of their ecological requirements and of their interaction at the edge of their respective distributions, as this should provide the basis for appropriate management and it would allow to determining whether allopatry, sympatry or intergradation occurs in these areas.

In recent years, several initiatives have been taken to follow up on some of those recommendations. Some preliminary results have been published on the respective distribution and habitat of the two species in the Horn of Africa, and a mitochondrial DNA analysis has revealed the deep genetic divergence between them. However, specific field studies have yet to be undertaken on the behavior, ecology and habitat requirements of P. aethiopicus; although the Desert warthog is a species still virtually unknown at the present time, it may indeed prove to be one of the most specialized of all suids.

Detail of mandible: Top: Ph. aethiopicus (BM 50.8.24.25); Bottom: Ph. africanus (BM 36.3.30.12). Note: Ph. africanus has usually 3 pairs of lower incisors; in Ph. aethiopicus lower incisors are absent, or vestigial and non-functional

While several papers have described in detail the differences between the skulls and teeth patterns of P. aethiopicus and P. africanus, no publication has yet illustrated them and reported the differences of external appearance between the two species. The differences between these two species that have lived side by side in vast areas (N Kenya, SE Ethiopia, Somalia) where a great deal of collection and scientific investigation took place in the last century, were rarely noticed in museum material and never noticed in the field. This suggests that no strikingly different features distinguished them in the field.

However, the internet and contribution from a number of field investigators have now provided good photographic reference sources, allowing the comparison of large series of close-up pictures of these two species. The aim of this short note is to offer a visual reference framework which can help field observers and scientists to easily distinguish Desert warthogs from Common warthogs, on the basis of a limited number of representative pictures. Two series of photographs are presented here: one illustrating the distinctive features of their skull and dentition, and a second allowing comparison of differences in their external morphology. The authors recognize that there may be additional permanent features that are specific of each species, but these would need further research. Other differences have been noticed, but they may be attributable to local variations or natural variability. The characteristic differences presented here are based on the morphology of adults (particularly adult males), and are the most prominent that should consistently be checked for identification.

The principal features of the Desert warthog, P. aethiopicus, in comparison to the Common warthog, P. africanus, are:

1. Differences in cranial and dental features
The skull is relatively smaller, but proportionately shorter and broader.

Thickened zygomatic arches: the front part of the zygomatic arch is thickened by internal sinuses and swollen into a spherical hollow knob just in front of the jugal-squamosal suture (in the Common warthog, the zygomatic arch may be robust but it is never quite so thickened and there is no formation of a knob).

Enlarged sphenoidal pits: In the Common warthog the skull roof behind the internal nares is marked by two deep and distinct 都phenoidal pits? not found in any other African suid, while in the Desert species, these pits have expanded enormously, disappearing as distinct entities, so as to contribute to two vaults between the pterygoids, separated by a deep vomerine ridge.

Absence of incisors: there is never any trace of upper incisors, even in relatively young individuals, and the lower incisors, even if present, are rudimentary and non-functional, and reduced to 2 pairs maximum (whereas the Common warthog always has two upper incisors, though these may be lost in very old animals, and usually six functional lower incisors in the adult dentition of normal suine form);

2. Differences in external appearance
Several accounts of morphological differences in the external appearance of both species have been reported. Features like the paler color of the mane, lighter body size, or black markings on limbs, are not necessarily characteristic of the Desert warthog and do vary individually. On the basis of numerous pictures taken in the field in many parts of their range, the following features seem to be the best permanent and distinctive identification criteria:

Hook-shaped genal warts: in adult Desert warthogs, the genal (jugal) warts are always hookshaped, whereas they are cone-shaped in the Common warthog. There is, however, a large variation in the volume and the form of these warts, as well as in their orientation.

Tip of ears bent backwards: the tips of the ears in Desert warthogs are always bent backwards. This feature gives the impression that the animal have rounded or blunt tips to their ears and that the contour of the ear is angular. In contrast, Common warthogs have pointed, leaf-shaped ears, with a sinuous contour;

Swollen suborbital areas: the suborbital areas in Desert warthogs are swollen in the form of pouches that often extend to the base of the genal warts. These same areas in Common warthogs have never such a pronounced swelling;

Egg-shaped vs. Diabolo-shaped head: the comparatively broader skull of the Desert warthog and its shorter basi-occipital region give the impression that the head is more egg-shaped, whereas it looks more diabolo-shaped in the Common warthog. In addition to the following photographs, these various features are also illustrated by the comparative pictures of Common and Desert warthogs from NE Kenya and Ogaden shown in Boy (2002), the excellent pictures of Desert warthogs by Caron on Pigtrop (http://pigtrop.cirad.fr/fr/petits_curieux/SV_classification_Paethiopicus.htm), and the fine series of pictures of Common warthogs from Nairobi NP, published in Bradley (1972). respective projects in N Kenya and SE Ethiopia.


Desert Warthog Found In Tsavo East National Park And Tsavo West National Park
by De Jong , Y. A., Culverwell, J. and Butynski, T. M. Suiform Soundings Vol 8(2), 2009

Both species of warthog, the common warthog Phacochoerus africanus and the desert warthog Phacochoerus aethiopicus, occur in Kenya. The desert warthog may be Africa's least known non-forest large mammal as its distribution is poorly understood and it has never been the focus of an ecological or behavioral study. None of the earlier books and field guides on the mammals of eastern Africa mention the desert warthog, and no game laws recognize this. Kingdon (1997) is the first major work to recognize the desert warthog as a full species and to bring this species to the attention of a large audience. The preliminary distribution map for the desert warthog compiled by d辿uart & Grubb (2001) presents only four localities for Kenya. They show the southern-most locality as Mkokoni, 60 km northeast of Lamu Island (north coast of Kenya). d辿uart & Grubb found no evidence for desert warthog south of the Ewaso Ng段ro River in central Kenya or west of the Tana River in eastern Kenya. They questioned whether the common warthog and the desert warthog might be sympatric at some sites.

D辿uart & Grubb (2005) produced a photographic guide that highlights the diagnostic differences between the common warthog and the desert warthog. Some of the main diagnostic phenotypic characters used to identify the two species of warthog in the field are as follows: common warthogs have pointed ear tips, cone-shaped genal warts, a 租iabolo-shaped head (when viewed from the front), and the suborbital areas are not swollen (fig. 1); desert warthogs have ear tips that are lax and flipped back, hook-shaped genal warts, an 粗gg-shaped head (when viewed from the front), and swollen suborbital areas (fig. 2).

Figure 1: Adult male common warthog Ph. africanus on the plains of the Laikipia Plateau, central Kenya. Note the pointed ears, the cone-shaped warts, the 租iabolo-shaped檀ead, and the lack of swelling of the suborbital area.

Figure 2: Adult male desert warthog Ph. aethiopicus in medium-dense shrub in Tsavo West National Park, southern Kenya. Note the flipped-back ear tips, the hooked warts, the broad, ç²—gg-shaped? head, and the swollen suborbital area.

In 2005, we started to opportunistically collect distribution data for both species of warthog in Kenya. TMB and YdJ found desert warthogs 15 km and 80 km west of Garissa town in 2005 when they encountered two solitary individuals in medium-dense Acacia bushland during a primate survey. These are the first records west of the Tana River and extend the geographic range to ca. 265 km northwest of Mkokoni, the nearest locality mentioned by d辿uart & Grubb (2001).

In 2007, JC, J. Feely, and S. Bell-Cross visited Tsavo East National Park south of the Voi River. Although they encountered no common warthogs during this trip, they did observe two sounders of desert warthogs in low bush on the edge of the Dika Plains, ca 13 km north and northwest of Buchuma Gate. Photographs were taken and sent to experts for confirmation. Some of these photographs, together with some of our other warthog photographs, are available for viewing on an online digital map.

These observations considerably extend the known geographical range for the desert warthog (ca. 310 km south from the nearest Garissa sighting and ca. 320 km southwest from Mkokoni). JC made two further visits to the Tsavos in 2007. He found both species of warthog in Tsavo West National Park and desert warthog north of the Voi River in Tsavo East National Park. In 2008, TMB and YdJ visited Tsavo West National Park and observed several sounders both of common warthogs and desert warthogs. In the northwest of the Park, in low bush on the edge of riverine forest, they found a sounder of six common warthogs only 150 m from a sounder of four desert warthogs. This locality represents not only the south western-most site in the range for desert warthog (ca. 390 km from Mkokoni, the southern-most point of d辿uart & Grubb 2001), but it also provided the first evidence that common warthog and desert warthog are at least narrowly sympatric over this part of their geographic ranges. Although we have yet to find the common warthog in Tsavo East National Park, it would be surprising if this species were not present there. If not present, however, the common warthog would need to be deleted from the list of large mammals known for Tsavo East National Park. As concerns the desert warthog, Tsavo East National Park and Tsavo West National Park can now add one more species to their already impressive list of large mammals.