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Species Name: Zanzibar Ader’s Duiker (Cephalophus adersi)
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A small forest-dwelling antelope, Ader’s duiker, was known from the Zanzibar Island in the Indian Ocean only. The species formerly occurred in the coastal forests of East Africa, but by 1978, it was confined to the Zanzibar Island by a small population. Due to indiscriminate slash-and-burn agricultural practices and uncontrolled timber cutting, forest cover on Zanzibar has been greatly reduced since the mid-1800s. By 1980, there was said to be only 615 ha of closed forest remaining. The Ader’s duiker was forced to take to the thickets and undergrowth of forest patches and ravines. Pressure on its habitat and direct hunting caused a continuous decline in its population, and today it is considered extinct on the Zanzibar Island. Duiker is the Dutch and Afrikaans name for a diver. This comes from their practice of diving into tangles and undergrowth when alarmed. They are small, typically 15-70 kg, usually solitary African antelope species belonging to the subfamily Cephalophinae. They get their name from the pronking or diving display they do when alarmed. There are around 20 species of duiker. Ader’s duiker is one of the largest. It is similar in appearance to the larger (55-80 kg) bushbuck, though somewhat more robust.
Today we report on the latter of these two species. Recent field research has led to a detailed study of Ader’s Duiker and the first comprehensive overview of this species in terms of its distribution, status, ecology, and importance. The CEPF Eastern Africa, Western Indian Ocean Marine and Coastal, and the World Wildlife Fund have been key supporters of this work. Due to the large wealth of information accrued, we report Ader’s Duiker in a series of briefs. The first investigates the distribution of this species throughout Unguja and Pemba islands. The following briefs will later be posted on this site and investigate issues concerning the conservation status and hunting pressure, habitat preference, activity and ranging behavior, and the diet of Ader’s Duiker.
The Coastal Forests of Eastern Africa biodiversity hotspot is a unique and diverse environment, exhibiting the highest level of plant and animal endemism on the continent. Zanzibar remains the stronghold for many species characteristic of these forests, however, the majority of Zanzibar’s terrestrial habitats have been highly modified by humans during the past 2000 years. Consequently, the majority of the island’s fauna has disappeared but despite centuries of exploitation and habitat destruction, Zanzibar still has two highly endemic and unique larger mammals. These are the Zanzibar Red Colobus (Procolobus kirkii) and the Ader’s Duiker (Cephalophus adersi).
Being a forest duiker, the Ader’s duiker is adapted to a forest life. There are hardly any open spaces on the main Zanzibar island where this animal could retreat to compared with Pemba and hence duiker behaviour cannot be adequately noted. The still-hunted status of this duiker, and loss of habitat through deforestation and agricultural over-cultivation in the two centuries to the present day has, at the very least, disallowed these mammals to enjoy the freedom and safety of their ancestors. Ader’s duiker would have been no less confiding than the Pemba Duiker where there is no hunting, living in a territory and protecting it against all other pairs of the species except when its young are mature, and escaping predators only through maximum use of its agility. Despite this forced change of habit, intelligence and resistance have allowed the Zanzibar duikers to survive better than most species, and the Ader’s duiker can still be found within the temperate secondary forest of the central plateau. This species possesses many adaptations for forest life. Its long legs make it a good fast runner, with a maximum speed of about 40 km/h. This is its main passive defence against predators. The hooves are small and the relative length of the bones of the legs means that a duiker has a well-coordinated, alternate pace from each pair of legs, increasing the length of time before it becomes tired out. This is essential, as duikers engage in long chases on narrow winding forest routes to confuse predators and finally escape. Nails are retained on all the cloven hooves, which are broad and slightly splayed, aiding mobility probably by increasing the surface area of ground in contact with the hoof. This is in comparison to the bushbuck, which has broad hooves only on the front legs for stability when feeding from shrubs, and the common duiker, which tends to have narrower hooves with shorter legs than Ader’s.
Ader’s duiker occurs in most thicket or forested areas of Zanzibar but is most readily seen in the Jozani Chwaka Bay National Park, where they are relatively habituated and can be found on the forest edge in the early morning or late afternoon. The behavior of staying at the forest edge is typical of this species, and they are rarely encountered more than a few meters from the edge of good forest. Unfortunately, while the park should be considered the best place to see Ader’s duiker, visitor numbers have increased in recent years, and the construction of an attractive new boardwalk through the forest to view the red colobus monkeys is likely to increase disturbance, making the future of duikers in the park uncertain. A major conservation success would, in fact, be if the population of this popular primate species increased to the extent that a new population of Ader’s duiker, translocated from Uzi Island, would become viable. This would result in these being the only two extant populations of this species.