Macaca nigra


789


FIG. 2 The functional relationships of predicted occupancy, with standard error, of M. nigra, with covariates included, in the best-fit models (Table 3): (a) protective area status, (b) forest cover (bush/scrub or closed canopy forest), (c) Euclidean distance from forest edge (negative values for cameras in non-forested habitat), and (d) Normalized Difference Vegetation Index (NDVI).


p = 0.66 and ψ = 0.28 (Table 2). By taking this estimate for occupancy and extrapolating it to all sites across the landscape (n = 796 or 3148 km2), we estimated the area of occupancy of M. nigra to be 2,101 km2. Finally, our goodness-of-fit test (χ2 = 1869,P= 0.65) indicated no evidence for a lack of fit for the most saturated model, suggesting that the more parsimonious models provide an adequate description of the data. According to our criteria of predicted occupancy .0.7 and continuous forest cover .50 km2, we identified eight distinct regions that probably contain important subpopulations (Fig. 3, Supplementary Table 3, Supplementary Fig. 2).


Optimal study design and power analysis


Considering the estimates from our averaged model and assuming constant probabilities, an optimal survey design would have 123 camera-trap sites, each with 8 repeats (1.5 months when each repeat constitutes a duration of 5 days) to achieve a target standard error of 0.05 (Fig. 4a).However, for camera traps further repeats are easily gained, without incurring further cost, by simply delaying the retrieval of the cameras. Therefore, it is possible to reduce the number of sites


needed by increasing the number of repeats,without addition- al cost, and thereby reducing overall survey costs. Under this option, if the number of repeats is increased to 18 (90 days, or c. 3 months), the number of camera-trap sites could be reduced to 90 (Fig. 4b). As the cheapest means of surveying M. nigra with suitable precision, this is the protocol that we advocate. Simulating the power provided by this protocol, if applied across multiple seasons, 3 years would be sufficient to detect a 10% decline in occupancy with 80% certainty.


Discussion


Our study demonstrates an extension in the known range of M. nigra compared to previous data. We show that camera-trap data coupled with occupancy analysis can provide a robust baseline assessment of a predominantly ground-dwelling forest primate of conservation concern. We estimated an occupancy of 0.66 (2,101 km2) for M. nigra, which represents the first baseline for future re- gional monitoring of the species. Estimated occupancy was only slightly higher than the naïve occupancy (0.64), which is probably an artefact of a long survey duration, which resulted in a high cumulative detection probability,


Oryx, 2020, 54(6), 784–793 © The Author(s), 2020. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605319000851


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