Forest ungulates in West Africa are common bushmeat species and are subject to habitat degradation through deforestation. Based on historical data, there are possibly 12 species of forest Bovidae and Tragulidae found in eastern Sierra Leone. We used camera trapping to assess occupancy by forest ungulates on and around a small protected area, Tiwai Island, Sierra Leone. We then assessed habitat over two field seasons during 2008–2011 for those species where we had sufficient numbers of detections. We detected 6 of 12 potential species and obtained enough data to further assess the habitat of two species. Species detected included the black duiker (
The Upper Guinea forests of western Africa contain some of the most diverse animal species on Earth and are global hotspots for conservation (Klop, Lindsell & Siaka
Few studies have been conducted on duikers and other forest ungulates of western Africa, although they are a major food source for villagers in many rural forested areas (Anadu, Elamah & Oates
Duikers and other forest ungulates are commonly utilised for bushmeat in rural areas throughout Guinea Rainforest, bringing food and an economic benefit to people of all social statuses (Anadu et al.
The purpose of this study was to determine occupancy of the Tiwai Island region by forest ungulates. To focus on bovid-related species, the red river hog (
Our study was conducted on and around the Tiwai Island Wildlife Sanctuary in southeastern Sierra Leone (
Tiwai Island Wildlife Sanctuary, Lower Tiwai, and the surrounding small islands in eastern Sierra Leone, surveyed using camera traps during 03 November 2008–22 February 2009 and 10 May 2010–23 July 2011.
Camera traps were employed to detect duikers and forest ungulates because of their efficiency in collecting data on elusive or shy species (Swann et al.
Species of duikers and ungulates were identified from the images captured by cameras, and each species was recorded as detection (1) or non-detection (0). Data were combined into two 7-day periods for season 1, and three 7-day periods for season 2, in which one or more detections within the 7 days warranted presence in the period. On the lower island, there were delays retrieving the cameras, which continued to collect data for 10–12 days after the end of the third period. We extended the detection time frame to three periods in season 2 to potentially capture more rare events. Although possibly making the models more robust, we controlled for possible detection bias by analysing the data with season as a covariate.
For species with sufficient detection, data were modelled using program PRESENCE for analysis, and the success of the habitat parameters was compared. Five habitat covariates were used in modelling occupancy: the understory density (Cover), understory type (Understory), canopy type (Canopy), whether the camera was on a human, animal or no trail (Trails) and the standardised distance to the Moa River (distMoa). Covariates had multiple parameters: cover was classified as open, semi-dense or dense; understory was woody, swamp, riparian or bush fallow; canopy was young secondary, mature, swamp, riparian or bush fallow; and trails were human trail, animal trail or no trail. We measured the strength of our models using the Akaike’s Information Criterion (AIC), which represents the goodness-of-fit of the models. The models were compared using the change in the AIC value (Δ AIC); the best-fitting model had a Δ AIC of 0.00, with the value increasing for less-fitting models. All models with a Δ AIC less than 4.00 were considered a good fit. We then calculated the occupancy probability and 95% confidence interval of each parameter.
We detected 6 of the 12 potential ungulate species on Tiwai Island Wildlife Sanctuary and vicinity over two seasons (838 and 2474 camera-trap days, for seasons 1 and 2, respectively) (
Potential and observed species of Bovidae and Tragulidae found on and in the vicinity of Tiwai Island, Sierra Leone, using camera traps during 2008–2011.
Species | Scientific name | IUCN status | Number of detections |
---|---|---|---|
Black duiker | LC | 2 | |
Bongo | NT | 1 | |
Bushbuck | LC | 9 | |
Maxwell’s duiker | LC | 201 | |
Water chevrotain | LC | 42 | |
Yellow-backed duiker | LC | 58 | |
Zebra duiker | VU | 0 | |
Jentink’s duiker | EN | 0 | |
Red-flanked duiker | LC | 0 | |
Ogilby’s (Brooke’s) duiker | LC | 0 | |
Forest buffalo | LC | 0 | |
Bay duiker | LC | 0 |
IUCN, International Union for Conservation of Nature; LC, least concern; NT, near threatened; VU, vulnerable; EN, endangered.
Maxwell’s duikers were the most commonly trapped with 175 photographs, or 5 detections per 100 trap nights. Yellow-backed duikers were recorded 55 times or 2 detections per 100 trap nights. Water chevrotains had 40 total detections or 1 detection per 100 trap nights. There were eight photographs of bushbucks, 0.24 detections per 100 trap nights. Bongo and black duiker were each detected once during the study, less than 0.03 detections per 100 trap nights (
In season 1, naïve occupancy estimate (ψ) was 0.30. Occupancy of Maxwell’s duiker was influenced by both the distance to the Moa River and understory type (
Occupancy analysis of Maxwell’s and yellow-backed duikers determined from camera trapping data on Tiwai Island and vicinity, Sierra Leone, during 03 November 2008–22 February 2009 and 10 May 2010–23 July 2011.
Season | Species | Model | AIC | Δ AIC | AICw | |
---|---|---|---|---|---|---|
1 | Maxwell’s duiker | ψ (distMoa) p (.) | 3 | 123.11 | 0.00 | 0.43 |
ψ (Understory) p (.) | 5 | 123.89 | 0.78 | 0.29 | ||
ψ (.) p (.) | 2 | 125.10 | 1.99 | 0.16 | ||
ψ(.) p (t) | 3 | 127.03 | 3.92 | 0.06 | ||
2 | Maxwell’s duiker | ψ (Canopy) p (.) | 6 | 372.38 | 0.00 | 0.35 |
ψ (Understory) p (.) | 5 | 372.63 | 0.25 | 0.31 | ||
ψ (.) p (t) | 4 | 372.84 | 0.46 | 0.28 | ||
Yellow-backed duiker | ψ (Understory) p (.) | 5 | 223.44 | 0.00 | 0.53 | |
ψ(.) p (t) | 4 | 226.31 | 2.87 | 0.13 | ||
ψ (distMoa) p (.) | 3 | 226.58 | 3.14 | 0.11 | ||
ψ (Cover) p (.) | 4 | 226.74 | 3.30 | 0.10 |
Note: Best-fitting models (Δ AIC < 4) from duiker habitat occupancy analysis.
AIC, Akaike’s information criterion.
Δ AIC, 0 indicates the best-fitting model for the data.
Duiker occupancy of specific Tiwai Island habitat parameters for best-fitting models (Δ AIC < 4) used in analysis.
Season | Species | Covariate | Parameter | ψ | SE | 95% CI |
|
---|---|---|---|---|---|---|---|
1 |
Maxwell’s | Understory | Woody | 0.77 | 0.35 | 0.07 | 0.99 |
Duiker | Swamp | 0.83 | 0.50 | 0.00 | 1.00 | ||
Riverine | 0.83 | 0.50 | 0.00 | 1.00 | |||
Bush fallow | - | - | - | - | |||
2 |
Maxwell’s | Canopy | Young secondary | 0.71 | 0.09 | 0.50 | 0.85 |
Duiker | Mature | 0.65 | 0.11 | 0.43 | 0.83 | ||
Swamp | 0.75 | 0.28 | 0.14 | 0.98 | |||
Riverine | - | - | - | - | |||
Bush fallow | - | - | - | - | |||
Understory | Woody | 0.69 | 0.08 | 0.52 | 0.82 | ||
Swamp | 0.83 | 0.25 | 0.14 | 0.99 | |||
Riverine | 0.28 | 0.17 | 0.07 | 0.68 | |||
Bush fallow | - | - | - | - | |||
Yellow-backed | Understory | Woody | 0.70 | 0.21 | 0.24 | 0.94 | |
Duiker | Swamp | - | - | - | - | ||
Riverine | - | - | - | - | |||
Bush fallow | - | - | - | - | |||
Cover | Open | 0.92 | 0.34 | 0.00 | 1.00 | ||
Semi-dense | 0.51 | 0.24 | 0.14 | 0.87 | |||
Dense | 0.30 | 0.23 | 0.05 | 0.78 |
Note: Standard error and 95% confidence intervals are included. Dashes indicate that insufficient detections in that habitat type were collected for analysis.
CI, confidence intervals; SE, standard error.
03 November 2008–22 February 2009;
10 May 2010–23 July 2011.
ψ, naïve occupancy estimate.
In season 2, the naïve ψ was 0.50. Occupancy of Maxwell’s duikers was associated with canopy cover and understory type (
We did not have enough detections of yellow-backed duikers in any habitat during season 1 to run working models. However, in season 2, we obtained a naïve occupancy rate of 0.26. The best-fitting model of season 2 was understory type, although the only significant parameter was woody habitat with ψ = 0.70 (±0.21 SE) (
Forest ungulates can be secretive and solitary animals which make them difficult to detect and estimate abundance. Camera trapping provides access to these species and can assist in cost-effective conservation efforts in regions where dramatic changes in land use and other human activity might be rapidly impacting species.
Our detection of half of the potential species that might be found in this region suggests that despite significant negative impacts of a long civil war, chronic deforestation in the region and continued bushmeat trade, at least some species are apparently quite resilient. Those species not detected might simply have been undetected, are extirpated or are marginal in distribution for the region or habitat. Based on known habitat, some species, such as forest buffalo; and zebra, bay, Ogilby’s and Jentinks’ duikers may have historically occurred in this area but were not detected during our study. Red-flanked duikers are more of a savanna edge species, but were included because they are found to the north of our study area, and might actually respond to deforestation in the region. In addition, we had very few detections of some important species, such as bongo and black duiker, which may have persisted at low numbers following the civil war or are recolonising the region from protected areas associated with the Gola Forest and further from Liberia.
Water chevrotains had one of the largest numbers of detections, suggesting that they are commonly found in this protected area. They are not as commonly found in bushmeat markets as some of the duikers, but if larger species continue to be overharvested, hunters may turn to the smaller chevrotains (Anadu et al.
Our camera trapping survey demonstrated that Maxwell’s and yellow-backed duikers occupy a variety of habitats. Riverine, woody and swamp habitats were similarly utilised during season 1, whereas in season 2 swamp was occupied most often, followed by woody habitat. Riverine habitat was occupied infrequently in season 2. This suggests that while they do use all three habitats, they may use them for different needs. Detections of Maxwell’s duikers also changed dramatically during our camera trapping periods, suggesting that longer-term studies may be needed to study them fully.
Yellow-backed duikers did not occupy the islands as extensively as Maxwell’s duikers, and appeared more specific in their habitat preferences. They were detected in open woody, understory or old forests. Decreases in populations of yellow-backed duikers throughout this area could occur as human impacts on land use continue to meet increasing demands for food. Detection rates of yellow-backed duikers varied throughout the second season, suggesting that they utilise both Tiwai Island and the mainland, and perhaps often travel between the two. Long-term studies may be needed for this species to fully understand their habitat usage and range.
As human activity continues to change natural landscapes, more species are losing suitable habitat and facing increased hunting pressure, resulting in decreasing populations. Bushmeat hunting is unlikely to diminish in the future unless other sustainable food sources are established. Illegal poaching makes it difficult to enforce hunting regulations, especially as the majority of poaching occurs in less accessible areas. In some areas, farming of wild meat species, such as the cane rat, has become an alternative to unregulated snaring and shooting. However, this management practice poses concerns for solitary species that do not reproduce often. Cryptic species are difficult to study and provide a particular challenge when trying to manage for conservation.
We would like to thank the communities of Tiwai Island for their support, as well as the Tiwai Island Administrative Committee and the Ministry of Agriculture Forestry and Food Security for granting us permission to work on Tiwai Island. Finally, we would like to acknowledge the hard work of our local field assistants, Kenewa Koroma, Bockary Koroma, Alusine Koroma and Mohamed Lahai.
The authors declare that they have no financial or personal relationships which may have inappropriately influenced them in writing this article.
K.R.M. analysed data and wrote the manuscript. E.B. summarised photos and wrote the first draft of the manuscript. A.L.C. designed the study and carried out field research. J.P.C. supervised the research, analysed data and wrote the manuscript.
Funding for the main project was provided by Conservation International, Tulsa Zoo Conservation Grant, Minnesota Zoo Ulysses S. Seal Conservation Grant, Oregon Zoo Future for Wildlife Grants Program, Columbus Zoo Conservation Fund, Riverbanks Zoo Conservation Support Fund, OKC Zoo Conservation Action Now, Idea WILD, the Young Explorer’s Fund and the IUCN Hippopotamus Specialist Group. Additional funding was provided by the Warnell School of Forestry and Natural Resources, University of Georgia and the School of Natural Resources, University of Nebraska.