Cephalophus adersi 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Cetartiodactyla Bovidae

Scientific Name: Cephalophus adersi Thomas, 1918
Common Name(s):
English Aders' Duiker
Taxonomic Notes: Aders' Duker has been considered both as a species and as conspecific with C. harveyi and C. natalensis. It was regarded as a full species by East et al. (1988) and by all subsequent authors. Recent research has shown that it occurs sympatrically with C. harveyi in the Boni-Dodori region of Kenya (Andanje et al. 2011, Amin et al. 2015).

Assessment Information [top]

Red List Category & Criteria: Vulnerable A4cd ver 3.1
Year Published: 2017
Date Assessed: 2016-09-28
Assessor(s): IUCN SSC Antelope Specialist Group
Reviewer(s): Cooke, R.
Contributor(s): Bowkett, A. & Finnie, D.
The global population of Aders' Duiker is now estimated at possibly ca 20,000 individuals (14,000 mature individuals) due to the recent discovery of large populations in the Boni-Dodori forest complex in northern Kenya. However, overall a decline greater than 30% is suspected over three generations (14 years: 2013-2027), since the start of insurgency and counter-insurgency operations in the Boni-Dodori region. This decline is suspected due to the continuing threats of hunting, habitat loss, lack of effective protection, feral dogs across their range and the presence of armed groups and insecurity in the lower Tana region where most of the population occurs. Aders' Duiker is therefore listed as Vulnerable under criterion A4. The population estimates likely reflect the maximum and ongoing declines may also qualify the species under criterion C1 in the near future. The status of the population on Zanzibar remains Critically Endangered.
Previously published Red List assessments:

Geographic Range [top]

Range Description:Aders' Duiker was previously believed to be endemic to the main island of Unguja, Zanzibar, the type locality, but was subsequently found to occur in the Arabuko-Sokoke Forest on the Kenyan coast, northwest of Kilifi. Kingdon (1982) described the species as widespread in the forests, woodland and thickets north of Mombasa (Kenya) almost up to the Somali border, although he only mapped it in Arabuko-Sokoke.

Gwynne and Smith (1974) reported the presence of Ader's Duiker in the Boni Forest on the Kenya-Somalia border, but this report has been generally overlooked. The report was cited by Abel and Kille (1976) who said the species was probably still present in wooded parts of Bush Bush Game Reserve in south-west Somalia.

In 2004, an Aders' Duiker was sighted in the Dodori National Reserve north of the Tana River Delta on the north Kenya coast (Andanje and Wacher 2004). Since then extensive camera-trapping work has found that Aders' Duiker is the most frequently recorded antelope in the Boni-Dodori forests, comprised of Dodori National Reserve, Boni Forest Reserve and Boni National Reserve (Andanje  et al. 2011a,b; Amin et al. 2015). This region forms the stronghold of the species. Boni National Reserve lies on the border with Somalia and the distribution may still extend into contiguous habitat on the Somali side, though there are no confirmed recent records.

There is a possibility that Aders' Duiker may have once occurred on Fundo Island, off the coast of Pemba Island (Williams 1998) and is reported to have been introduced on to Funzi Island, Pemba (Kingdon 1997), but has since become extinct on both these islands. Archer and Mwinyi (1995) mention, "unconfirmed (but) reliable reports (which) indicate a thriving population on Tumbatu Island". Further confirmation of this is yet to be forthcoming. In February 2000, five Aders' Duikers were translocated to Chumbe Island from mainland Zanzibar, where a female was already in place. Five individuals were also translocated to Mnemba Island off the north-east coast of Unguja in 2005 and are breeding (Fiske 2011, K. Siex pers. comm. in Williams 2013).
Countries occurrence:
Kenya; Tanzania, United Republic of
Additional data:
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:To date, three surveys have been carried out within Zanzibar. The first in 1982 (Swai 1983) estimated the Aders' Duiker population to be in the region of 5,000 individuals. A second, more detailed survey undertaken in 1995 (Williams et al. 1995) placed the population at below 2,000. The populations were shown to be located in five main subpopulations with varying degrees of interconnectedness: Kiwengwa Forest in the north, localities in the central Jozani-Chwaka Bay area and Mtende in the south. A third survey carried out in 1999 (Kanga 1999) placed the population at 614 ±46 within the same study area as Williams et al. (1995). This represents a substantial decline in the calculated population over a 17-year period. However, as each survey method used different methodologies, the results are not directly comparable. Nevertheless, it is evident that there has been a significant decline in the Unguja population in recent decades.

In Arabuko-Sokoke Forest, Aders' Duiker was once considered common but is now considered scarce (Williams 2013). An extremely approximate figure (extrapolated from three individuals) of around 500 individuals was estimated in 1999 based on a drive-count survey (Kanga 2002b). Recent surveys have only sighted very low numbers (three in 1999, two in 2002 and two in 2003) (Kanga 2002a,b, 2003).

Aders' Duiker has been shown to be common in Boni-Dodori forests, with occupancy of very close to or at 100%, suggesting that this species is consistently distributed through this region (Amin et al. 2015). An overall density of 7.3 duikers/ km² (95% CI 4,5–10,1 duikers/km²) was obtained by Amin et al. (2015) for Boni National Reserve based on a replicate count N-mixture model for camera trap data. If this figure is applicable to the three forests of Dodori National Reserve (877 km²), Boni Forest Reserve (450 km²) and Boni National Reserve (1,339 km²) then the population across the Boni-Dodori forest complex could be 19,500 individuals (95% CI 12,000-27,000 individuals). A global population of ca 20,000 (14,000 mature individuals)—but declining—is therefore possible. However, it is not clear whether the density figure is applicable to all three forests, given differences in protection status and zoning.
Current Population Trend:Decreasing
Additional data:
Number of mature individuals:14000Continuing decline of mature individuals:Yes
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:A species of dense coastal forest and thicket. In Zanzibar, Aders' Duiker inhabits tall, undisturbed coral rag thicket known locally as 'msitu mkubwa' (Archer 1994). In the Arabuko-Sokoke Forest, the species inhabits Cyanometra forest (Kanga 2002b). Aders' Duiker is a browser selecting for dicotyledenous leaves, seeds, sprouts, buds and fruits (Swai 1983); and although sensitive to habitat disturbance, it occasionally occurs in secondary thicket (Williams et al. 1995, Kanga 1999).
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):4.8

Use and Trade [top]

Use and Trade: There has been a long tradition of hunting Aders' Duiker in Zanzibar and Kenya. In Zanzibar, there is likely to have been an increase in hunting pressure following the revolution of 1964 after which enforcement of the wildlife laws became largely non-existent. However the Department of Commercial Crops, Fruits and Forestry (DCCFF) has since begun to address the hunting situation in Zanzibar. Although despite its highly threatened and declining status on Zanzibar, trophy hunting of Aders’ Duiker was advertised in 2014 and has recently begun (Anon 2016). In the Arabuko-Sokoke Forest hunting and snaring are common. Over 2,600 households live within 2 km of the forest and at least 33% carry out hunting and/or trapping (FitzGibbon et al. 1995). The Boni-Dodori forest complex likely faces similar if not greater hunting pressures, due to ongoing military activity within the region.

Threats [top]

Major Threat(s): The major threats to Aders' Duiker are hunting and habitat loss. Although hunting has come under an increasing level of control in Zanzibar (both at the village and governmental level), it remains a significant threat to this population (Finnie 2002); with this exacerbated by the recent initialisation of trophy hunting on the island (Anon 2016). In Zanzibar there has been a substantial amount of deforestation and forest degradation over the last 30 years. Firewood is the primary source of income for a significant proportion of people living near the forest (Ely et al. 2000) and there are few alternative means of income generation. This has led to loss of habitat for Aders' Duiker, but also severe habitat fragmentation.

The East African coastal forests (Arabuko-Sokoke and Boni-Dodori forests) experience illegal hunting, with the impact of local subsistence hunting likely to be much higher in the smaller but much more heavily populated Arabuko-Sokoke N.R. (Amin et al. 2015). In the Boni-Dodori landscape, there is widespread deforestation and habitat fragmentation, due to clearance for agriculture and unsustainable use of forest resources, such as for charcoal production (Andanje et al. 2011b). Insecurity affects the whole region which is not safe for visitors (KWS 2013). Poaching has decimated many species in the Kiunga-Boni-Dodori-Conservation Area and livestock incursions into Boni and Dodori N.R.s are frequent, especially during droughts, with livestock brought from Garissa, Mandera and Wajir counties (KWS 2013). Boni and Dodori N.R.s have no management system or management presence, leaving them open to uncontrolled resource use and illegal activities such as poaching; Dodori N.R. has 20% of its area designated as a high-use zone and 37% as low use (KWS 2013). Boni and Lunghi forest reserves are similarly unmanaged and are not clearly demarcated (World Agroforestry Centre 2014). Since 2013, insurgency and counter-insurgency operations have severely affected Boni N.R. in particular, and the impact of numerous soldiers and armed groups is potentially severe.

Major agricultural and transport developments in the Tana valley have been proposed—especially the Lamu Port and Lamu-Southern Sudan-Ethiopia Transport (LAPSSET) corridor—which if implemented are expected to have a considerable impact on the main range of the species.

Conservation Actions [top]

Conservation Actions: Recent findings strongly indicate that the Boni-Dodori forest system is the most important known population centre for Ader's Duiker (Amin et al. 2015); and therefore securing these animals into the future is a priority. Both Boni N.R. (1,339 km2) and Dodori N.R. (877 km2) are formally protected, but neither currently has a management presence. The species is known to occur in Boni F.R. and may also occur in Lunghi F.R., between Boni and Dodori. Both sites were managed by the local counties, but have now been gazetted as Boni-Lunghi State Forest (399 km2) (Government of Kenya 2016). Arabuko-Sokoke F.R. (420 km2) is an important protected area in southern Kenya; and Jozani-Chakwa Bay N.P. and Kiwengwa Pongwe F.R. have secured part of the Aders' Duiker range on Zanzibar. Aders' Duiker has been protected under Tanzanian law since 1919, while in Kenya Aders' Duiker is a protected species. 

An investigation into the feasibility and efficacy of a captive breeding programme on Zanzibar was undertaken in December 2001 (Finnie 2001). An in-country captive-breeding programme has also been proposed for Kenya (Kanga 2001) but not yet implemented.

The species’ range (except most of Boni F.R.) lies within the Coastal Forests of East Africa biodiversity hotspot. Boni and Dodori N.R.s are part of the Kiunga-Boni-Dodori Conservation Area (KWS 2013) and the whole Boni-Dodori region is part of the Tana-Kipini-(Kenya) and Laga Badana (Somalia) Landscape (World Agroforestry Centre 2014).

Citation: IUCN SSC Antelope Specialist Group. 2017. Cephalophus adersi. The IUCN Red List of Threatened Species 2017: e.T4137A50182159. . Downloaded on 20 September 2017.
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