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Bruce, T.; Wacher, T.; Ndinga, H.; Bidjoka, V.; Meyong, F.; Ngo Bata, M.; Olson, D.
Camera-trap survey for larger terrestrial wildlife in the Dja Biosphere Reserve, Cameroon
2017  Yaound‚, Cameroon: Zoological Society of London (ZSL) & Cameroon Ministry of Forests and Wildlife (MINFOF): 3-85

The medium- to larger-bodied terrestrial fauna of the northwest portion of the Dja Biosphere Reserve (DBR) was surveyed using camera-traps. An array of 41 infrared-triggered trail cameras (Bushnell Trophy Cam Aggressor), each roughly 2 km apart in a square grid pattern, was placed for a combined c. 3,725 operational days for a wildlife survey in late 2015 and early 2016 with 7,109 wildlife events recorded. The estimated species richness converged at 148 days. This suggests that most, if not all, medium-to-large (>0.5 kg) terrestrial mammals species present in the area were detected during the survey. A total of 32 mammal species were detected, including Western lowland gorilla (_Gorilla gorilla gorilla _- Critically Endangered species under IUCN Red List criteria), the Endangered central chimpanzee (_Pan troglodytes troglodytes_), African forest elephant _(Loxodonta africana_ - Vulnerable), mandrill (_Mandrillus sphinx_ - the first record of this large species in the reserve), bongo (_Tragelaphus eurycerus_ - Near Threatened), white-bellied pangolin (_Phataginus tricuspis_ - Vulnerable), and giant pangolin (_Smutsia gigantea_ - Vulnerable). This first systematic camera-trap survey for medium-to-large terrestrial mammals in the Dja Biosphere Reserve has provided evidence that it remains an important protected area for the conservation of medium-to-large terrestrial mammals in the Congo Basin. This contradicts previous reports (Steyn 2015). Despite pervasive bushmeat hunting and intensifying illegal trade in elephant ivory, pangolin scale, and great apes, the survey has documented continued presence of all these species in a small sample area (3-4% of the greater reserve) located relatively close to permanent settlement (that is, from 6 to 19 km). The detection of several species on the IUCN Red List of Endangered Species highlights the persistence of populations of these vulnerable species within the reserve. Thus, the Outstanding Universal Values of the DBR as highlighted by the UNESCO World Heritage Site Designation (http://whc.unesco.org/en/list/407/), that is, the large block of contiguous rainforest and diverse wildlife populations, at least for the sector surveyed, remain intact as of 2016. Due to the large, variable home ranges of forest elephant, chimpanzee, and gorilla that exceed this survey's inter-trap distances of 2 km, the positive relationship between occupancy and abundance cannot be relied upon as with species with smaller home ranges, such as the duiker species. The relative abundance of forest elephant as measured by trapping rate was higher in the camera-trap survey area than those recently found by sign surveys (MINFOF & IUCN 2015). This observation may be due, in part, to forest elephants moving seasonally within the forest as the MINFOF & IUCN and this survey were conducted in a different season. From the data gathered in this camera trap survey, we believe that the status of the larger terrestrial vertebrate fauna of the Dja Biosphere Reserve falls, most likely and within the zone of the camera trap grid, in the Diminished Fauna category (the third-level of a faunal intactness continuum that ranges from intact, relatively intact, diminished, depleted, to an 'empty forest' status). All the larger vertebrates, except for wild felids, perhaps, still occur within the Dja Reserve, albeit likely at diminished abundances. The presence of larger-bodied duikers also supports this categorization as they often are rare or extirpated under intensive hunting. Camera-trap surveys are complementary to line transect distance sampling surveys, recce encounter data, and patrol-based direct encounter data for monitoring target wildlife populations. Camera-trap surveys record a much greater proportion of the larger vertebrate fauna than do line transect and recce surveys that are best-suited for gathering data (direct observations and sign) for larger-bodied species that leave noticeable sign, such as nests and dung, and for arboreal primates and birds. Thus, the overall 'intactness' status of the larger cursorial vertebrate fauna (that is, the terrestrial megafauna) within a protected area can be better estimated using camera-trap surveys. However, the distance sampling data obtained through line transect and recce encounter rate surveys allows for more reliable abundance estimates and greater sensitivity to changes in populations for gorilla, chimpanzee, and forest elephant whose sign (dung and nests) can be dated. Camera-trap surveys are likely more reliable than distance and encounter rate sampling at detecting these species when their numbers are low.

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