Biogeography and conservation of desert warthog Phacochoerus aethiopicus and common warthog Phacochoerus africanus (Artiodactyla: Suidae) in the Horn of Africa

3.1 Historic distribution

Phacochoerus aethiopicus appears to be endemic to Ethiopia, Somalia, and Kenya. We found no P. aethiopicus records for Djibouti. This species is, however, recorded for Duddarp, northwest Somalia, about 18 km from Djibouti. Phacochoerus aethiopicus occurs in Kenya less than 12 km from Tanzania. As far as we are aware, there is no record of this species for Tanzania. Locality records are almost all from east of the Eastern (Gregory) Rift Valley (ERV), the exceptions being north Ethiopia and northwest Somalia where P. aethiopicus occurs on the graben (= floor) of the ERV (Figure 3; Table 1).

3.2 Sympatry

There are five known, widely-spaced, areas of sympatry between P. aethiopicus and P. africanus (Figure 3); central east Ethiopia (3300 km²), north Somalia (3300 km²), central Kenya (four sites; 13,400 km²), north coast of Kenya (two sites; 8000 km²), and southeast Kenya (five sites; 14,100 km²).

At Suyian Ranch, on the Laikipia Plateau, central Kenya, one mixed-species sounder was encountered in 2021 (Figure 4; Butynski and De Jong 2021). In addition, the authors observed individuals here that they judged to be atypical for either P. aethiopicus or P. africanus.

Figure 4:

Adult male desert warthog Phacochoerus aethiopicus (left) and adult male common warthog Phacochoerus africanus on Suyian Ranch, Laikipia, central Kenya. To the best of our knowledge, this is the first photograph of these two species together. Photograph by ©Yvonne de Jong and Tom Butynski.

3.3 Altitude

The known altitudinal range of P. aethiopicus is from sea level to 1895 m asl (Suyian Ranch, Laikipia, central Kenya), with most of the geographic distribution <1000 m asl (Figure 5; Table 2). Phacochoerus africanus occupies a much broader altitudinal range in the HoA, occurring from sea level to 3500 m asl (Bale Mountains, central south Ethiopia), with most of the geographic distribution between 1000 m asl and 2000 m asl. Although these two species overlap in altitude from sea level to 1895 m asl, P. aethiopicus is primarily a lowland species while P. africanus is primarily a mid-altitude and highland species (Butynski and De Jong 2018, 2021; De Jong and Butynski 2014, 2018; d’Huart and Grubb 2001).

Figure 5:

Geographic distribution of desert warthog Phacochoerus aethiopicus and common warthog Phacochoerus africanus in the Horn of Africa relative to altitude.

As mentioned above, the ‘Phacochoerus Shapefile’ does not distinguish between the two species of Phacochoerus and is, therefore, not included in Table 2. Nonetheless, in some cases, the ‘Phacochoerus Shapefile’ strongly suggests altitudinal limits that are greater than those presented in Table 2. Here is a summary of where we suspect these maps extend the altitudinal limits beyond those given in Table 2.

Eritrea: Yalden et al. (1984) show Phacochoerus near Asmara (2300 m asl). The P. africanus buffer zone for Mogo (1730 m asl; Abraha 2016) also reaches Asmara. There is no record for P. aethiopicus in Eritrea, the nearest record to Asmara being 665 km to the southeast at Duddarp, northwest Somalia (Figure 5). It is, therefore, highly probable that the altitudinal range for P. africanus in Eritrea is 0–2300 m asl.

Ethiopia: Künzel et al. (2004) found P. africanus at Lake Abbe, Djibouti, near Ethiopia at 240 m asl (Figure 5). The buffer zone for P. africanus at Lake Abbe runs into Ethiopia at the same altitude. It is probable that the altitudinal range for P. africanus in Ethiopia is about 240–3500 m asl.

Djibouti: Yalden et al. (1984) show Phacochoerus at sea level west of Tadjoura. The buffer zone for the Forêt de Day record for P. africanus (Table 2) also reaches the coast of Djibouti. It is, therefore, likely that the altitudinal range for P. africanus in Djibouti is 0–1440 m asl. There is no record for P. aethiopicus in Djibouti, the nearest record to Tadjoura being about 90 km to the southeast at Duddarp, Somalia (Figure 5).

Somalia: Phacochoerus africanus occurs on the north coast of Somalia where the lowest altitudinal record is 30 m asl (Table 2). This species occurs at sea level just south of Somalia on the north coast of Kenya (Figure 5). Mandheera (960 m asl) represents the highest confirmed altitudinal record for P. africanus in Somalia. D. Mallon (pers. comm. 2021), however, observed Phacochoerus at Daallo at 2130 m asl in Buxus-Juniperus habitat. It is probable that the altitudinal range for P. africanus in Somalia is 0–2130 m asl.

Kenya: Given that P. africanus occurs to 3500 m asl on the Bale Mountains, 7° north of the equator in Ethiopia (Table 2), its known highest altitude in Kenya (2385 m asl on the equator) is surprisingly low. This is especially unexpected given the similarities in the montane and alpine plant community, and that many of the other species of large mammal on the volcanic Bale Mountains (e.g., Yalden et al. 1984) achieve greater altitude on Kenya’s highest volcanic mountains (Coe and Foster 1972; Moreau 1944a,b; Young and Evans 1993). Nonetheless, the distribution maps in Stewart and Stewart (1963) and Kingdon (1979) do not show records above the foothills of Kenya’s three highest mountains; Mount Elgon, Aberdare Range, and Mount Kenya. This also corresponds to the other literature (e.g., Butynski 1999; Butynski and De Jong 2016; Young and Evans 1993). Similarly, on Mount Kilimanjaro, in north Tanzania on Kenya’s south border, there is no record for P. africanus above the foothills (Child 1965; Grimshaw et al. 1995; Guest and Leedal 1954; Moreau 1944a; True 1892).

3.4 Rainfall

Mean annual rainfall over the geographic distribution of P. aethiopicus ranges from 100 mm (northeast coast of Somalia) to 1200 mm (central Kenya; Figure 6; Table 3). Most records are from regions where mean annual rainfall is between 200 mm and 500 mm. Mean annual rainfall over the geographic distribution of P. africanus ranges from about 50 mm (southeast Eritrea and north coast of Somalia) to 1950 mm (central Kenya and west Ethiopia), with most records from areas where mean annual rainfall is 200–1200 mm.

Figure 6:

Geographic distribution of desert warthog Phacochoerus aethiopicus and common warthog Phacochoerus africanus in the Horn of Africa relative to mean annual rainfall.

Rainfall is low and temperatures are high (see below) along the south coast of the Red Sea, south coast of the Gulf of Aden, and west coast of the Indian Ocean, but these extreme conditions are often ameliorated by the high humidity that results from the proximity to these large bodies of warm water and the mist carried inland by the Northeast Trades (Kingdon 1990). On the north coast of Somalia, where some sites support both species, mean annual rainfall is as low as 50 mm (Berbera) but mean relative humidity is 67% (mean monthly range = 44–81%). On the coast of Eritrea, P. africanus occurs where mean annual rainfall is 219 mm (Massawa) but mean relative humidity is 66% (mean monthly range = 54–76%). These levels of humidity help support a higher level of plant growth and greater plant diversity than would otherwise be possible in these low rainfall regions. Regardless of the high humidity, neither P. aethiopicus nor P. africanus occurs where mean annual rainfall is <50 mm (e.g., in the vicinity of Boosaaso and Cape Guardafui near the east tip of the HoA; Figure 6).

3.5 Temperature

Mean annual temperature over the geographic distribution of P. aethiopicus ranges from as low as 17 °C (central north coast of Somalia and Laikipia, central Kenya) to as high as 31 °C (Lugh, south Somalia; Figure 7; Table 4), while mean annual temperature across the geographic distribution is typically between 20 °C and 27 °C. The extremes are about 5.5 °C (Ceerigaabo, north Somalia) and 49 °C (Berbera, north Somalia; weatherspark.com).

Figure 7:

Geographic distribution of desert warthog Phacochoerus aethiopicus and common warthog Phacochoerus africanus in the Horn of Africa relative to mean annual temperature.

Mean annual temperature over the geographic distribution of P. africanus ranges from as low as 8 °C (Aberdare Range, central Kenya, and Bale Mountains, central south Ethiopia), to as high as 32 °C (central Djibouti and Assab, southeast Eritrea), while mean annual temperature across the geographic distribution is typically between 15 °C and 25 °C. Temperature can drop to about −7 °C in the Web Valley, Bale Mountains (C. Gordon pers. comm. 2018), and reach 45 °C at Tadjoura, Djibouti.

3.6 Biomes, biotic zones, and ecoregions

In the HoA, P. aethiopicus and P. africanus both occur mainly in the ‘Tropical and Subtropical Grasslands, Savannas, Shrublands, and Woodlands Biome’, but also in the ‘Deserts and Xeric Shrublands Biome’, and the ‘Tropical and Subtropical Moist Broadleaf Forest Biome. In addition, P. africanus occurs in the ‘Montane Grasslands and Shrublands Biome’.

Figure 8:

Geographic distribution of desert warthog Phacochoerus aethiopicus and common warthog Phacochoerus africanus in the ecoregions of the Horn of Africa (Burgess et al. 2004; Olson et al. 2001).

Most of the geographic distribution of P. aethiopicus lies within the ‘Somalia-Masai Bushland Biotic Zone’ (Happold and Lock 2013). This is White’s (1983) ‘Somalia-Masai Regional Centre of Endemism’. This biotic zone has a long history of isolation and aridity, and is characterised by low, very unpredictable, and highly variable rainfall.

Phacochoerus aethiopicus occurs in at least seven ecoregions (Figure 8; Table 5). See Figure 2.2 in Burgess et al. (2004) and Figure 2 in Olson et al. (2001). Most of the geographic distribution of this species lies in the ‘Somali Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’, while there is also substantial presence in the ‘Northern Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’ and ‘Northern Zanzibar-Inhambane Coastal Forest Mosaic Ecoregion’

Phacochoerus africanus is present in at least 15 ecoregions in the HoA, but particularly in the ‘Northern Acacia-Commiphora Bushlands and Thickets Ecoregion’, ‘Somali Acacia-Commiphora Bushlands and Thickets Ecoregion’, ‘Ethiopian Xeric Grasslands and Shrublands Ecoregion’, and ‘Ethiopian Lower Montane Forests, Woodlands, and Bushlands Ecoregion’.

The only ecoregion where P. aethiopicus is present, but where P. africanus is apparently absent, is the ‘Hobyo Grasslands and Shrublands Ecoregion’ which is located along the east coast of Somalia. This highly distinct ecoregion, also known as the ‘Obbia’, is marked by dune grasslands with a sparse covering of bushes, small shrubs, and herbs adapted to the persistent sand-laden winds (Kingdon 1979, 1990; White 1983).

The five regions of sympatry between P. aethiopicus and P. africanus occur in five ecoregions (Figures 3 and 8). This indicates considerable similarities in the physiology, ecology, and behaviour of these two species, and that the major differences are not likely to be determined without detailed studies in areas with extreme climatic conditions.

3.7 Habitats

Phacochoerus aethiopicus appears to prefer relatively flat and sandy ground with open areas of short, perennial grass in Acacia spp. woodland and Acacia spp./Commiphora spp. bushland. Edges of water courses, swamps, lakes, drainage lines, vegetation mosaics, and bases of rocky outcrops offer the habitat characteristics that seem favoured by P. aethiopicus. On Suyian Ranch, P. aethiopicus and P. africanus both appear to prefer abandoned cattle bomas (livestock enclosures or kraals) where nutritious grasses are dominant, particularly Cynodon spp. (T. Butynski and Y. de Jong pers. obs.). Burrows are probably a prerequisite. Phacochoerus aethiopicus apparently occurs where perennial sources of drinking water are unavailable. Elliot (1897, p. 110) states, “They appeared to be somewhat independent of water, for we met them in the middle of the Haud where certainly the nearest water-hole must have been 50 miles away, too far one might suppose for them to seek daily.”

Of the two species, P. africanus occupies a wider range of habitats, but is typically a species of open country; grasslands, open bushlands, open woodlands, savanna, pans, floodplains, glades, and vleis. This species is most abundant on alluvial soils in lightly wooded vegetation mosaics where water is always present (Butynski and De Jong 2018; Grubb et al. 1998; Skinner and Chimimba 2005), but also occurs, at least at low density, where perennial sources of water are not available (Bigourdan 1948; Butynski and De Jong 2018; Dorst and Dandelot 1970; Smithers 1971). Phacochoerus africanus is also present in some forests where it is probably reliant on large open areas of short grass (Deribe et al. 2008; Künzel et al. 2004; Yalden et al. 1996).

Phacochoerus africanus requires burrows for thermal-regulation, water conservation, sleeping, giving birth, rearing young, and predator-avoidance, yet does not dig its own burrows (Bradley 1971; Cumming 1975; Geigy 1955). These are typically modified aardvark Orycteropus afer burrows, but sometimes those of Cape crested porcupineHystrix africaeaustralis or North African crested porcupine Hystrix cristata are used, as well as rock caves and underground erosion gullies (Butynski and De Jong 2018; Cumming 1975; Guiraud 1948; Shortridge 1934; White and Cameron 2009). Orycteropus afer is very broadly, if not completely, sympatric both with P. aethiopicus and P. africanus, while Hystrix spp. occurs over most of the geographic distributions of these two species, with the notable exceptions of Djibouti and Somalia.

4.1 Ecology

Consistent with the findings of d’Huart and Grubb (2001), P. aethiopicus is endemic to Ethiopia, Somalia, and Kenya. This species is not known to occur at altitudes >1895 m asl, nor where mean annual rainfall is <100 mm or >1200 mm or where the mean annual temperature is <17 °C or >31 °C (Table 6). It appears that the geographic distribution of P. aethiopicus is more limited by altitude, rainfall, and temperature than is P. africanus. The altitudinal range of P. africanus overlaps that of P. aethiopicus from sea level to 1895 m asl, but extents to 3500 m asl (Table 6). Examination of major environmental gradients, shown in Table 6, indicate that P. africanus is able to live in more extreme environments than P. aethiopicus.

The geographic distribution of P. aethiopicus is restricted to low altitude, semi-arid, landscapes east of the ERV, only occupying the graben of the ERV in north Ethiopia and northwest Somalia (Figure 3). Here the graben is wide (>300 km) and the escarpment is relatively gradual and low. In contrast, the geographic distribution of P. africanus is not limited by the ERV. The ERV appears to be an ecological barrier for P. aethiopicus south of N 9.6°. It is likely that the relatively high annual rainfall (>1250 mm) and lower mean annual temperatures (<17 °C) associated with the higher altitudes of the east escarpment of the ERV (>1895 m asl) cannot be tolerated by P. aethiopicus, especially the young.

The skull of P. aethiopicus is slightly smaller than that of P. africanus (Grubb 1993). Although body measurements for P. aethiopicus are lacking, it appears (in the field) to be the marginally smaller species, as well as more gracile with less muscle mass (at least over the hindquarters) and relatively longer legs. These characters give P. aethiopicus a relatively greater body surface area than P. africanus. In addition, P. aethiopicus often appears lean with wrinkled (‘desiccated’) skin, whereas P. africanus typically appears fat with tight skin. It may be that P. aethiopicus has less capacity to accumulate sub-dermal fat than does P. africanus. Both species, but particularly P. aethiopicus, have a sparse pelage that affords little protection from the cold. While these traits probably provide an advantage to P. aethiopicus in extreme heat, they are likely disadvantages under conditions of cold and drought.

At the northeast extreme of the ERV, P. aethiopicus occurs on the graben of the ERV at Biye Bahi (920 m asl) and Duddarp (185 m asl; Figure 5). In three regions south of N9.6°, the east escarpment of the ERV is <1895 m asl (lower Omo River Basin, southwest Ethiopia; Lake Turkana Basin, northwest Kenya; Lake Magadi Basin, central south Kenya). In two of these relatively low regions, P. aethiopicus reaches the east escarpment of the ERV; Yabelo Wildlife Sanctuary (>1430 m asl) east of the Omo River and south of Baragoi (1425 m asl).

Phacochoerus aethiopicus occurs mainly in the ‘Somali Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’ and ‘Northern Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’ (Figure 8). Both of these ecoregions are low in altitude, relatively flat, and arid to semi-arid, with a mean annual rainfall that can fluctuate greatly year to year (<100 mm/year to 600 mm/year; Burgess et al. 2004), and temperatures that can reach >38 °C. A small part of the geographic distribution of P. aethiopicus lies in the ‘Northern Zanzibar-Inhambane Coastal Forest Mosaic Ecoregion’. This ecoregion is also low in altitude, mostly flat, and relatively wet with a mean annual rainfall of <1000–2000 mm (Burgess et al. 2004). Located along the north coast of Kenya and along the Tana River, this ecoregion represents a transition zone between the ‘Somali Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’ to the north and the ‘Northern Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’ to the west. Another small part of the geographic distribution of P. aethiopicus lies in the hot and dry ‘Hobyo Grasslands and Shrublands Ecoregion’ of east Somalia (see above). Maximum temperature over most of this ecoregion is between 30 °C and 33 °C, while mean annual rainfall ranges from 200 mm to 430 mm. The highest temperatures occur over the south part of this ecoregion (38 °C at Mogadishu) where mean annual rainfall is 429 mm.

The south extreme of the geographic distribution of P. aethiopicus is a region of sympatry with P. africanus. This is where the ‘Northern Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’ meets the ‘Southern Acacia-Commiphora Bushland and Thickets Ecoregion’. There is no evidence for P. aethiopicus in the ‘Southern Acacia-Commiphora Bushland and Thickets Ecoregion’, the north-most extent of which reaches the Kenya-Tanzania border.

A broken chain of highlands and mountains runs northeastwards along the southeast escarpment of the ERV from central Ethiopia almost to the tip of the HoA at Cape Guardafui (Figure 5; Happold and Lock 2013). Along this chain, in central east Ethiopia, lie the Hararge Highlands, while farther to the northeast, across a lowland gap (where Hargeysa is located), are the Ogo Highlands (= Galgodon Highlands). The Ogo Highlands include the range of mountains that runs along the north coast of Somalia from Mandheera eastwards to near Cape Guardafui. It appears that the population of P. africanus on the foothills of the Hararge Highlands is now isolated from the population on the foothills of the Ogo Highlands. The presence of these two currently disconnected populations suggests that the Hararge Highlands and Ogo Highlands were once part of a more homogeneous ecosystem that has since been fragmented by geologic and climatic changes.

4.2 Estimated geographic distribution

Our best estimates of the current geographic distributions in the HoA for P. aethiopicus and P. africanus (Figure 9) are based on the historic map for Phacochoerus (Figure 3), their altitudinal and climatic limits (Table 6), as well as ecoregions, threats, and conservation status.

Figure 9:

Estimated current geographic distribution of desert warthog Phacochoerus aethiopicus and common warthog Phacochoerus africanus, and the areas of sympatry, in the Horn of Africa.

The geographic distribution of P. aethiopicus extends from southeast Kenya north to the Red Sea and Gulf of Aden, and from the east flank of the eastern escarpment (below 1895 m asl) of the ERV eastwards to the Indian Ocean (Figures 3 and 9). The estimated current geographic distribution is 1,109,000 km² (45% of the land surface of the HoA; Figure 9). This includes most of central and east Kenya, all but the driest parts of southeast Ethiopia (mean annual rainfall <200 mm), and all but the driest parts of Somalia (mean annual rainfall <100 mm). The only records for P. africanus over the vast region comprised of east Ethiopia and Somalia come from Berbera and Dhur Cilaan in extreme north Somalia. We expect that P. africanus also occurs in Daallo (extreme north Somalia) which lies in the ‘Somali Montane Xeric Woodlands Ecoregion’.

The estimated current distribution of P. africanus in the HoA is shown in Figure 9. Since P. africanus is present on the north coast of Kenya, where it is sympatric with P. aethiopicus, we expect it to also occur in the ‘Northern Zanzibar-Inhambane Coastal Forest Mosaic Ecoregion’ in extreme south Somalia. Phacochoerus africanus occurs within and west of the ERV throughout the HoA. The estimated current geographic distribution of P. africanus in the HoA is 1,213,000 km² (49% of the land surface of the HoA; Figure 9).

4.3 Threats and conservation

Phacochoerus aethiopicus and P. africanus are both listed as ‘Least Concern’ on the IUCN Red List of Threatened Species (De Jong et al. 2016a,b). Both species do relatively well in regions unsuitable for growing crops. Outside the HoA, P. africanus is widespread, locally abundant and, in some areas, expanding its geographic distribution (e.g., South Africa; Swanepoel et al. 2016). Nonetheless, overall, the abundance and geographic distribution of both species continues to decline. The ultimate cause of this decline in the HoA is humans, the populations of which continue to grow rapidly in all five countries (see www.wildsolutions.nl/warthogbase). Details on the threats to the long-term survival of P. aethiopicus and P. africanus are presented in Butynski and De Jong (2018), De Jong and Butynski (2018), and De Jong et al. (2016a,b).

The ‘Somali Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’ (1,053,900 km²) and, to a lesser extent, the ‘Northern Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’ (326,000 km²), are the strongholds for P. aethiopicus. The ‘Somali Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’ is the second richest ecoregion in the HoA in terms of the number of endemic vertebrate species (49). As such, it is regarded as ‘Globally Outstanding’ in WWF’s Biological Distinctiveness Index (Burgess et al. 2004). The ‘Northern Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’ is the richest ecoregion in the HoA in terms of the number of vertebrate species (1012; Burgess et al. 2004). The ‘Somali Acacia-Commiphora Deciduous Bushlands and Thickets Ecoregion’ is among Africa’s top 10 ecoregions with the highest extinction risk scores (Burgess et al. 2004). To the northwest, the ecoregions of the Ethiopian Highlands on both sides of the ERV, where P. africanus is present, also have an outstanding biodiversity. They are, however, listed as “Critically Threatened” as they are among Africa’s ecoregions with the highest percentage of habitat loss (Burgess et al. 2004).

Phacochoerus aethiopicus occurs at low densities over most of its geographic distribution and there are large areas within the distribution polygon where it is apparently absent (De Jong and Butynski 2018; De Jong et al. 2016a). In Arawale NR, central east Kenya, Njoroge et al. (2009) report a mean density of 0.8 individuals/km, with highest densities in thickets (1.3 individuals/km). Low abundance or absence are likely a result of scarcity of food and perennial water, given the low annual rainfall throughout much of the geographic distribution and the great variability and extremes of rainfall. For example, mean annual rainfall at Mogadishu is 429 mm but varies more than 16-fold, from 60 mm to 1000 mm (Ashford 1998).

Rainfall is strongly correlated with plant productivity and, thus, food for herbivores. The lower the annual rainfall, the higher the annual rainfall variability and, therefore, the greater the variability of plant foods for herbivores. Jones and Thornton (2013) and Thornton (2014) used the coefficient of variation of mean annual rainfall as a measure of rainfall variability. Phacochoerus aethiopicus typically lives under conditions of considerably higher annual rainfall variability and, therefore, probably food variability, than does P. africanus. Over the northeast 20% or so of the HoA, where the mean annual rainfall is <250 mm, annual rainfall variability is >45%. Over most of the remainder of the geographic distribution of P. aethiopicus, where mean annual rainfall is 200–500 mm, annual rainfall variability is >30%. Much of the geographic distribution of P. africanus in the HoA receives a mean annual rainfall of 200–1200 mm. Here rainfall variability ranges from 15% to 40%. It may be that, while P. africanus is able to survive under a greater range of altitude, rainfall, and temperature than P. aethiopicus, the latter is able to cope with greater variability in the availability of water and food.

Where water and food are reliably available, P. aethiopicus can be common. Aggregations of up to 30 individuals occur in bushland around permanent wells and close to towns in Ogaden, southeast Ethiopia (Wilhelmi et al. 2004). Phacochoerus aethiopicus occurs at high density during the dry season on patches of green grass along the Ewaso N’yiro River in Samburu NR, central Kenya, and is sometimes common and confiding near small, remote, villages and lodges where hunting is absent (A. Caron pers. comm. 2004; De Jong and Butynski 2018; De Jong et al. 2016a; Grubb and d’Huart 2010).

Hybridization is important from a species conservation perspective as it is a potential threat. Currently, there is no solid evidence for hybridization between P. aethiopicus and P. africanus. Recent analyses of the genetic structure and phylogeography of Phacochoerus, based on the whole genome sequencing of four P. aethiopicus and 35 P. africanus, did not identify recent hybrids (Garcia-Erill et al. 2022). This result is, however, not surprising given the small sample size (n = 39). This study did, however, find one P. africanus from an area of sympatry in Kenya (Tsavo West NP) that showed signs of enhanced P. aethiopicus ancestry. As mentioned above, in an area of sympatry on the Laikipia Plateau, several individuals judged to be atypical for either P. aethiopicus or P. africanus were observed (Butynski and De Jong 2021). In short, on-going hybridization between P. aethiopicus and P. africanus cannot be excluded.

4.4 Protected areas

Phacochoerus aethiopicus occurs in at least 12 protected areas in Kenya [Arawale NR (533 km²), Boni NR (1339 km²), Buffalo Springs NR (131 km²), Dodori NR (877 km²), Kora NP (1787 km²), Losai NR (1806 km²), Meru NP (870 km²), Samburu NR (165 km²), Shaba NR (239 km²), Tsavo East NP (13,747 km²), Tsavo West NP (7065 km²), and Ishaqbini Hirola Conservancy (72 km²)], and Ethiopia (Yabelo Wildlife Sanctuary; 2496 km²) (Culverwell et al. 2008; De Jong and Butynski 2014, 2018; De Jong et al. 2016a; d’Huart and Grubb 2001; Grubb and d’Huart 2010, 2013). This species is expected to be present in the Tana River Primate NR, Rahole NR, Bisanadi NR, Kenya, in Babile Elephant Sanctuary, Ethiopia, and in Daallo Mountain NP, Lag Badana-Bushbush NP, and Kismayo NP, Somalia. Phacochoerus africanus is present in many protected areas in the HoA.

Unfortunately, protected areas in the HoA typically face many challenges, particularly high levels of illegal activities (e.g., poaching, taking of fuelwood, timber, and charcoal, livestock grazing and browsing, and agricultural encroachment). Government funding is often insufficient for training, equipping, and supporting the required numbers of management, security, education, and research personnel. Corruption and mismanagement are other problems (Butynski and De Jong 2018; De Jong and Butynski 2014, 2018; De Jong et al. 2016a). In addition, parks and reserves are increasingly fragmented and isolated, lacking connectivity with other protected areas. This connectivity is essential for gene-flow and species range shifts, particularly in this time of rapid climate change (Saura et al. 2018).

4.5 Future research

As stated above, the natural history of P. aethiopicus remains poorly known. While this study addressed questions concerning the biogeography of Phacochoerus in the HoA, it also generated important questions, including:

1. Does P. aethiopicus occur in Djibouti, Eritrea, or Tanzania? Was this species historically present in these countries?

2. Does P. africanus occur in south Somalia?

3. Does P. africanus occur in Samburu NR, Buffalo Springs NR, or Shaba NR, central Kenya, and in Daallo Forest Reserve, north Somalia?

4. Which species is present in those areas depicted as ‘Phacochoerus sp.?’ in Figure 3?

5. Where else are P. aethiopicus and P. africanus sympatric?

6. Do P. aethiopicus and P. africanus hybridize?

7. What does the fossil record tell us about the historic distribution of P. aethiopicus and P. africanus?

8. Which subspecies of P. africanus are valid and what are their geographic distributions?

9. What is the diet of P. aethiopicus? How do the diets of P. aethiopicus and P. africanus differ?

10. Do P. aethiopicus and P. africanus differ in their dependence on sources of perennial water for drinking?

11. Do P. aethiopicus and P. africanus differ in the level of nocturnality?