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
Species Authority: Thomas, 1918
Common Name(s):
English Aders' Duiker

Assessment Information [top]

Red List Category & Criteria: Critically Endangered A4cd ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Finnie, D.
Reviewer(s): Masoud, T.S. & Plowman, A. (Antelope Red List Authority)
Listed as Critically Endangered as there has been an observed decline on Zanzibar from 5,000 individuals (1983), to 2,000 (1996) to 640 (1999). There are no recent population estimates, but on the basis that the known reasons for the decline are still occurring (i.e., a continued decline in the area and quality of habitat due to illegal wood-cutting, and the continuation of illegal hunting), it is suspected that the population will continue to decline at a similar rate.
Previously published Red List assessments:

Geographic Range [top]

Range Description:Aders' Duiker occurs on the main island of Unguja, Zanzibar, as a near endemic since, although the species has been described by Kingdon (1982) as widespread in the forests, woodland and thickets north of Mombasa (Kenya) almost up to the Somali border, in the light of rapidly shrinking suitable habitat, it would appear the population has succumbed to a severe decline in numbers. In the Arabuko-Sokoke Forest, northwest of Kilifi (Kenya), the species is still present, but very few substantiated sightings are made each year. This forest covers approximately 416.8 km². In 2004, what is thought to be an Aders' Duiker was sighted in the Dodori National F.R. north of the Tana River Delta on the north Kenya coast (Andanje and Wacher 2004).

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.
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. 1996) placed the population at below 2000. 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. (1996). This represents an 87.7±0.7% decrease in the calculated population size in 17 years. 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 population in recent decades.

The Kenyan population in Arabuko-Sokoke is probably even closer to extinction. A figure of around 500 individuals was estimated in 1999 based on a drive-count survey. However, this figure was extrapolated from just three individuals and is extremely approximate (Kanga 2002b). Recent surveys have only sighted very low numbers (three in 1999, two in 2002 and two in 2003) (Kanga 2002a, 2002b and 2003).
Current Population Trend:Decreasing
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:In Zanzibar, Aders' Duiker inhabits tall, undisturbed coral rag thicket known locally as msitu mkubwa (Archer 1994) of the Zanzibar-Inhambane regional mosaic (XIII). It is usually found singly, sometimes in pairs or trios and often, when encountered, may be following a troop of Sykes (Cercopithecus mitis albogularis) or Kirk's Red Colobus (Procolobus kirkii) monkeys feeding on discards and dislodged edibles from the canopy above (Swai 1983; Imani pers. comm. to Williams 1998).

Williams et al. (1996) found that Aders' Duiker has very specific habitat requirements. They were only found in older growth thicket areas and the highest population densities (11.4±5.18 per km²) were recorded in undisturbed high thicket. In contrast, Kanga (1999) did encounter the occasional Aders' in secondary thicket. In the Arabuko-Sokoke Forest, Aders' Duiker inhabits Cyanometra forest, one of three major habitat types dictated by local soils.

Aders' Duiker appears to be loosely diurnal (Williams et al. 1996), with a very acute sense of hearing and possibly smell (Archer 1994, Williams 1998). Aders' is a browser selecting for dicotyledenous leaves, seeds, sprouts, buds and fruits (Swai 1983). Territories are maintained by facial gland secretions on prominent twigs and faecal heaps (Swai 1983). No formal study of behavioural or ecological allopatric separation of Aders' Duiker with other small antelope has yet been attempted. Moreover, little is known about the population dynamics of this species or of its reproductive biology. Williams (in press) summarizes the available knowledge on the species.

Threats [top]

Major Threat(s): The major threats to Aders' Duiker are hunting and habitat loss.

There has been a long tradition of hunting 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. It would appear that, partly as a result of hunting, the mini-antelope populations of Zanzibar and, especially Aders' Duiker, have undergone long-term declines. The Department of Commercial Crops, Fruits and Forestry (DCCFF) began to address the hunting situation in Zanzibar in 1994. Although hunting has come under an increasing level of control in Zanzibar (both at the village and governmental level), it remains a significant threat at present (Finnie 2002). In the Arabuko-Sokoke Forest hunting and trapping 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). It is assumed that the high level of trapping represents a significant threat to the continued existence of Aders' Duiker in Kenya.

In Zanzibar there has been a substantial amount of deforestation and forest degradation over the last 30 years. This has led to loss of habitat for Aders' Duiker, but also severe habitat fragmentation. 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. Habitat destruction is probably the most significant threat to Aders' Duiker survival on Zanzibar.

The Arabuko-Sokoke Forest is one of the last major remnants of lowland forests on the East African coast, indicating the massive loss of habitat suffered by Aders' Duiker. Illegal wood-cutting continues to modify Aders' Duiker habitat and is assumed to negatively impact habitat quality. Wood-cutting continued to increase between surveys undertaken in 1998 and 2002 (Kanga 2002a). It is likely that habitat destruction will constitute the most difficult threat to address in terms of Aders' Duikers' future security.

Conservation Actions [top]

Conservation Actions: In Zanzibar, the revised version of the Aders' Duiker Species Recovery Plan (SRP) constitutes a framework for conservation of the species (Finnie 2002). In Kenya, a conservation and recovery plan has been proposed by Kanga (2002a).

Aders' Duiker has been protected under Zanzibar law since 1919, while in Kenya Aders' Duiker is a protected species.

In Zanzibar, the newly designated Jozani-Chakwa Bay National Park has secured part of the Aders' Duiker range within a strictly protected area. Another important subpopulation in Kiwengwa Forest is now protected as a nature reserve. In Kenya, the Arabuko-Sokoke Forest is designated as a National Park, part of which is a strict nature reserve. Further survey work is needed to determine whether a viable population persists in the Dodori National F.R.

Intensive fieldwork undertaken in the Arabuko-Sokoke Forest by the Kenya Wildlife Service has involved population surveys for Aders' Duiker and other species as well as monitoring illegal human activities. In 2003, fieldwork also involved the removal of animal snares from Aders' Duiker habitat.

In Zanzibar a community wildlife management programme commenced in 1995 in an effort to reduce antelope hunting to a more sustainable level. Village Hunter Associations have been set up to manage local wildlife. This will be continued and expanded. Community Forest Management Agreements are in place for the eight villages surrounding Jozani Forest, and the programme has been extended to cover most of southern Unguja. Part of these agreements involves the designation of high protection zones that allow extremely limited use of forest products. All five major subpopulations are covered by some form of community protection.

Conservation education programmes have had some success in increasing awareness in rural areas in both Kenya and Zanzibar. However, in Zanzibar a lot of work is still required in urban areas, the main market for firewood.

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).

Trophy hunting has also been suggested in Zanzibar as a conservation tool (Finnie and Ely 2001). However, for such a rare species, the likely success of this programme must be investigated thoroughly.

The status of Aders' Duiker needs to be monitored closely so the efficacy of the recovery plans can be judged and, if necessary, altered. A simple research programme to understand more about the behavioural and population ecology of Aders' Duiker is necessary.

Citation: Finnie, D. 2008. Cephalophus adersi. The IUCN Red List of Threatened Species 2008: e.T4137A10455260. . Downloaded on 16 August 2017.
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