Detecting wildlife poaching 577


two hypotheses (higher detection probabilities with spatially focused patrols and independent observers, respectively), but we did find evidence to support the third hypothesis (higher detection probability with systematic searches).


Discussion


FIG. 2 Kaplan–Meier survival curve of all imitation snares over time. The dashed lines show when snare searches were conducted.


along parallel lines resulted in 45% detection, and 42%of imitation snares were reported for the quadrant search pat- tern (Table 1, Fig. 3). The detection probability of parallel lines was significantly higher than the baseline detection probability (Fisher’s exact test, P = 0.04), as was the detec- tion probability of the parallel lines and quadrant searches combined (Fisher’s exact test, P = 0.03). The detection prob- abilities of spatially focused patrols and patrols with in- dependent observers were not significantly different from the baseline detection probability. We thus reject our first


6 5


4 3


2 1


Standard patrols (baseline) Spatially focused patrols Independent observers


Parallel lines Quadrant pattern


Detecting evidence of poaching activities is challenging, and low detection rates can lead to misinterpretations of the spa- tial distribution of such activities. Here, using snares as a case study, we outlined a method for estimating the prob- abilities of detecting wildlife poaching, and evaluating alter- native patrol strategies. The experimental design included a baseline measure of detection probabilities before alter- native strategies were implemented. Our findings showed that c. 23% of the 166 imitation snares were found by the end of the study. Even ifwe assume that snares are clustered, patrol teams must still find one to identify the cluster. Furthermore, the real poachers’ snares that were detected by the teams were all considered to have been placed some time before the study. From a conservation perspec- tive, this highlights the threat that snares pose; even snares that were set several months ago can still be harmful to wild- life (Hunter et al., 2007). Although detection probabilities were generally low, the highest proportion of imitation snares was detected with systematic search strategies.


Limitations


The study areawas small, and we used a relatively high den- sity of imitation snares (40 snares/km2). Based on previous studies and our experience, we expected detection probabil- ities to be low. Therefore, we used a high density of imitation snares to increase the total number of detections that could be used in our analysis. The estimated detection probabil- ities were based on the imitation snares considered available for detection (i.e. within a 10mbuffer around patrol routes) as opposed to all imitation snares in the study area. By only considering those imitation snares available for detec- tion, the estimated detection rates were probably inflated. Because the rangers’ responsibilities include other duties in addition to searching for snares, snare searches were con- ducted relatively infrequently, and only if resources were available. The imitation snareswere set at the end of the wet season,


0.00 0.25 0.50 Detection probability


FIG. 3 Density plot of detection probabilities by patrol strategy from 10,000 bootstrap samples. The density is the number of simulation runs with that particular detection probability.


0.75 1.00


when the vegetation in some areas was still relatively dense. From then until the last imitation snares were retrieved in October, the study area received little rain. As a result, the landscape gradually dried and vegetation cover decreased. The estimated detection probabilities in this study therefore reflect conditions during the dry season in a semi-arid landscape. The probability of detecting snares during the wet season is expected to be lower because of increased


Oryx, 2022, 56(4), 572–580 © The Author(s), 2021. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605320001301


Density


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164