Department of Commercial Crops Fruits & Forestry

Unguja’s overlooked mammals

see complete download
The small carnivors of Unguja
Results of a photosurvey in Jozani Forest Reserve, Zanzibar, Tanzania
Helle V. Goldman & Jon Winther-Hansen

Unguja, the main island in the Zanzibar archipelago, lies about 6° south of the equator and 40 km from mainland Tanzania and has an area of approximately 1600 km2. The deeper soil zone of the western part of the island formerly supported moist forest, while thicket and dry forest covered the coral rag zone of the east and much of the south.

The island has been separated from mainland Africa for ca. 10,000–15,000 years, permitting the evolution of several endemic mammal subspecies. With about 524,000 inhabitants, Unguja has a rural population density of some 170 persons per km2 (fi gures based on United Republic of Tanzania 1991; Zanzibar Revolutionary Government 1992). Rural Zanzibaris make their living from various combinations of cash crop and subsistence cultivation, livestock husbandry, fi shing, charcoal and lime production, harvesting and selling fuelwood, and hunting. Tourism plays an increasing role in the local economies of some rural areas.

Apart from measures generally addressing habitat destruction and degradation, mammalian wildlife conservation and research efforts on Unguja have tended to focus on a few currently endangered or potentially threatened species. One is the highly visible endemic Zanzibar red colobus monkey.

A habituated subpopulation of these charismatic primates draws thousands of foreign visitors annually to Jozani Forest Reserve, thereby funding local community development schemes. Far more diffi cult to observe, the near-endemic Ader’s duiker (Cephalophus adersi), like the other two species of small antelope found on the island, is of high local salience on account of its prized meat, which features in community rituals in some parts of Unguja. Ader’s duiker has received research and conservation attention in the form of population surveys, hunting management plans and a trial translocation.

The Zanzibar red colobus monkey and Ader’s duiker are considered Unguja’s two most important “indicator species” by the Dept. of Commercial Crops, Fruits and Forestry. The Zanzibar leopard (Panthera pardus adersi), an endemic subspecies , has been the focus of some research aimed primarily at documenting indigenous knowledge of, attitudes towards and practices relating to this felid.

In spite of Zanzibaris’ assertions that leopards continue to be sighted and occasionally attack livestock, attempts to demonstrate the leopard’s survival on Unguja have met with failure. In comparison to the colobus, Ader’s duiker and leopard, the island’s other terrestrial non-volant mammals have received little attention. These include a second monkey species, two or more species of galago, several species of shrew, two species of elephant shrew, several viverrid and herpestid species, one hyrax species, several rodent species and a suid.

Some are regarded as endemic subspecies or are on the IUCN’s Red List of Threatened Species. As noted above, the island is host to a number of smaller indigenous carnivore species, a group of animals which to our knowledge has not been the special subject of any signifi cant research in Zanzibar. These comprise the Zanzibar slender mongoose (Her pestes sanguineus rufescens), the Zanzibar bushy-tailed mongoose (Bdeogale crassicauda tenuis)—both subspecies endemic to Unguja, the African civet (Civettictis civetta) and the recently identifi ed Zanzibar servaline genet (Genetta servalina archeri).

Until our study, the Zanzibar servaline genet has been known to science solely on the basis of a single old skin and damaged skull. Virtually nothing is known scientifi cally of this animal’s behavior, ecology, abundance or distribution on the island. Our knowledge of Unguja’s other carnivores is scarcely better. The very recent scientifi c discovery of the genet on Unguja attests to this: serious research devoted to the island’s other carnivores would almost certainly have turned up the genet.

The approximately 90 vertebrate and 13 invertebrate species on this list “are to be totally protected year round and… are to be accorded the highest conservation action and work priority.” The African civet appears in Appendix 2 3, a list of about 240 vertebrates and 80 invertebrates “to be protected year round and…to be accorded the second highest allocation of protection and law enforcement efforts.” In addition to these indigenous carnivores, the literature refers to two introduced species on Unguja: the banded mongoose (Mungos mungo) and the small Indian civet (Viver ricula indica).

Both of these species are named in Appendix 4 of the 1996 Act. This is a list of “species which are not protected, are accorded no conservation priority and which may be captured and/or killed.” The purpose of this survey was to contribute toward our knowledge of Jozani’s small carnivores, with the larger objective of contributing to their conservation. It is obviously diffi cult to tailor conservation measures to protect fauna about which little is known, a problem which challenges the Integrated Conservation and Development Section of Zanzibar’s Dept. of Commercial Crops, Fruits and Forestry.

A general lack of appreciation for the islands’ wildlife—apart from a few highly salient species—is currently as much a problem as the lack of information. International attention to particular species or groups of species generates interest in those animals among relevant local offi cials. It is hoped that this will in turn lead to better formulated and better implemented conservation measures. The listing of many mammal (and other) species in appendices 1 and 2 of the 1996 Act has been a crucial step, but there is more to do.

Methods

The study area Zanzibar forms part of Conservation International’s Eastern Arc Mountains and Coastal Forests, one of the organization’s 25 global “Biodiversity Hotspots” (www.biodiversity hotspots.org/xp/Hotspots).

The native vegetation of Zanzibar has been classifi ed as Zanzibar–Inhambane regional mosaic and more recently as Eastern African Coastal Forest, of which there are several subcategories. Jozani Forest Reserve was selected as the study area. The reserve encompasses Unguja’s only remaining natural, older-growth forest and also comprises a mosaic of other habitats, including coral rag thicket, bracken fi elds, saltmarsh grassland and mangrove forests.

While people do make illegal use of the reserve, it is generally believed that Jozani is under less human pressure than surrounding areas which are afforded no legal protection or are under the control of local communities. Therefore, mammalian wildlife is thought to be at least as abundant and species-rich in Jozani as elsewhere on Unguja—and probably more so. Jozani Forest Reserve is in the south-central part of Unguja, pinched between Chwaka Bay to the north and Uzi Bay to the south. It measures approximately 25 km2, of which up to 4 km2 is groundwater forest which fl oods during the annual rains and is dominated by Eugenia sp. and Calophyllum inophyllum, with Pandanus sp., Vitex doniana and Elaeis guineensis as subdominants.

This part of the reserve can be classed under Coastal Riverine/Swamp/Groundwater Forest in Clarke’s classifi cation scheme. Adjacent to the natural older-growth forest is a former Calophyllum inophyllum plantation and a stand of Casuarina equisetifolia. Roughly two-thirds of Jozani Forest Reserve consists of thicketed coral rag, including such species as Euclea racemosa, Polysphaeria parvifolia, Pachystela brevipes, May tenus mossambicensis, Rus natalensis, Macphersonia gracilis, Annona senegalensis and Flueggia virosa. This vegetation cover would be classed as Eastern African Coastal Scrub Forest.

The thicket’s marked variation in its density, height and patchiness across the reserve is probably related to soil depth and quality (the soils are generally very shallow and poor; fossil coral outcroppings are common) and the level of human pressure. In some areas of thicket cattle are being grazed and wood is being extracted; other areas are evidently recovering from exploitation; yet other areas do not seem to have been disturbed in a very long time. Upgrading the reserve’s status to that of a national park was approved by the Government of Zanzibar on 31 December 2002.

This will entail a change of name, an increase in size, and the application of a different set of laws. The Jozani–Chwaka Bay National Park will be about 50 % larger than the former Jozani Forest Reserve, embracing more land to the west and northwest. Whereas Jozani Forest Reserve has been regulated by the 1996 Act, the new Jozani–Chwaka Bay National Park will fall under legislation contained in The Environmental Management for Sustainable Development Act, 1996.

Temperatures on Unguja are generally between 21 and 34 °C. The islands receive about 1600 mm of rain annually. Most precipitation falls during two rainy seasons in November–December and March–May. Humidity varies between 75 and 83 %. During the fi rst two weeks of our survey, which was timed to take place between the two rainy seasons, there were occasional brief, light showers in the mornings. Throughout the study, some days were overcast, especially in the early part of the day. In January, the sun rises at about 06:15 and sets at about 18:45; it begins to become light about 20 minutes before sunrise and it remains light for about 20 minutes after sunset. Daylight length varies by less than an hour during the year.

Results

Sixteen rolls of fi lm were used, yielding 73 photographs of wild mammals representing seven species: four carnivores, one primate, one rodent and one insectivore. In addition, two domestic species were photo-trapped. No birds or other animals were photo-trapped. More species were photo-trapped in the coral rag thicket (all 7 species) than the groundwater forest (3 species).

This could have been a function of the greater number of trap-nights in the thicket. Considering that the camera traps were in the groundwater forest for only 6 out of a total of 55 trap-nights, it is noteworthy that almost half the species photo-trapped during the entire survey were photo-trapped in the groundwater forest (3 species out of 7). Three of the four wild carnivore species photo-trapped during the survey were photo-trapped in the groundwater forest. All carnivore species photo-trapped in the groundwater forest were also photo-trapped in the thicket. Four species were photo-trapped using the active system; all 7 were photo-trapped with the passive system. Note that two of the additional mammal species photo-trapped with the passive system—the shrew (species?) and the red bush squirrel (Paraxerus palliatus)—are the two smallest bodied mammals photo-trapped in our survey. When mounting the active system, we routinely set the height of the beam at least 20 cm above the ground.

Consequently, the active system would have missed recording any visits by shrews, squirrels or other animals in that size range. Six of these species (including 3 of the carnivores) were photo-trapped during the fi rst 4 trap-nights of the survey, at the fi rst 3 locations established.

It then took a further 12 trap-nights to obtain photographs of the seventh species—the African civet (C. civetta). The number of species photo-trapped in a single location ranged from 0 to 4. Three locations yielded no photographs of wild species. One location yielded photographs representing 4 mammal species, all carnivores: between 22 and 26 January all 4 carnivores visited one camera trap at location 9. In fact, 3 species came within a few hours of one another during a single night/early morning at this location: on 23 January the servaline genet came at 01:22, the bushy-tailed mongoose came at 02:06, and two slender mongooses arrived at 06:26.

Trap-nights per species photo-trapped at each location ranged from 1 to 7. Trap-nights per species were greatest at the locations at which the camera traps stayed the longest: camera traps were at locations 9 and 10 for 14 trap-nights each, with 3.5 and 7 trap-nights per species, respectively. The two locations which produced photographs of the largest number of species were locations 9 (with 4 species photo-trapped and 3.5 trap-nights per species) and 1 (with 3 species photo-trapped and 1 trap-night per species). The species which proved “easiest” to trap was the servaline genet (G. servalina).

This viverrid was photo-trapped at four locations: two in the coral rag thicket and two in the groundwater forest. However, of the carnivore species, the servaline genet was the species which appeared in the fewest photographs: only 6 images. Inversely, the species photographed most often—31 photographs—was one of the two carnivore species photo-trapped at only two locations: the slender mongoose (H. sanguineus). The other was the African civet (C. civetta). Of the species photo-trapped, the slender mongoose seemed to be least disturbed by the camera.

Other species tended to fl ee after one or two pictures were taken (although they sometimes returned later the same night). We assume the fl ash and perhaps also the sound of the camera alarmed them. Because slender mongooses were active by day the fl ash may have been less disturbing to them. Defi ning night-time on Unguja in January as the hours of darkness from 19:00 to 06:00 and day-time as 06:01–18:59, we can say that no carnivore species were phototrapped during both day-time and night-time.

Based on their visits to the traps, we can infer that all species were either completely nocturnal or com p letely diurnal. Slender mongooses (H. sanguineus) triggered the traps only during daylight, from 06:26 to 18:53. This diurnal activity pattern is consistent with previously published fi ndings. Looking more closely at the timing of slender mongoose photographs shows that of 31 pictures, only 5 were taken after 07:29 in the morning and before 17:00 in the afternoon. This suggests a preference for mornings and afternoons, perhaps because of cooler temperatures or the activity patterns of prey. However, our own fi eld activity peaked during the middle hours of the day and this may have inhibited slender mongooses from moving about near the traps at that time. The slender mongoose was the only carnivore which we actually sighted during the course of our study.

Bushy-tailed mongooses (B. crassicauda), in contrast, were photo-trapped throughout the night, starting at 19:31, about half an hour after darkness fell, and ending at 05:41, about half an hour before sunrise (Table 7). This nocturnal activity pattern accords with scanty published information; little is known about this animal. Both herpestids were photo-trapped at two of the same locations (locations 2 and 9). Their visits to the camera traps were always separated by at least 38 minutes. Whereas bushy-tailed mongooses were photographed throughout the hours of darkness, African civets (C. civetta) were photo-trapped during more limited night-time hours, starting at 20:09 and ending at 03:42.

The nocturnal habits of the African civet are well-documented. The photo-trapping pattern for servaline genets (G. servalina) was similar to African civets: servaline genets were photographed starting at 19:56 and ending at 03:24. The two shortest intervals between recorded visits by different carnivore species was 38 minutes separating visits by the two mongoose species and 44 minutes dividing visits by a servaline genet and a bushy-tailed mongoose.

Mammals were usually photo-trapped singly. There were two exceptions: three Sykes’ monkeys (Cercopithecus mitis) were photo-trapped together at location 1, and two slender mongooses were photo-trapped together at location 9. Like other monkeys, Sykes’ monkeys are well-known to be highly social animals.

The two apparently adult-sized slender mon gooses photo-trapped together may have been siblings, parent and adult or adolescent offspring, a mating pair, or perhaps a coalition of males. Two domestic species entered the camera traps (Appendix 1). Domestic cattle were photo-trapped at location 7, where resulting photographs showed the herd clustering closely around the beef bait and investigating it.

What was probably the same herd had been encountered 5 days previously, near location 4. The approximately 20-head herd were in good condition on both occasions, indicating that they were feeding well. Dogs were photo-trapped at locations 5, 7, 9 and 10. The same individual dog visited multiple traps. A pack of dogs visited one camera trap. Most dogs were photo-trapped during daylight hours. The sleek and relatively well-fed condition of some dogs contrasted with the underfed, scruffy appearance of other dogs. This suggests that some dogs were feral whereas others belonged to hunters. These incidents were reported to offi cers at Jozani Station and Dept. of Commercial Crops, Fruits and Forestry headquarters.