Detecting wildlife poaching 575
team, often by using a map, where they should start their patrol. The rangers were again not informed about the research. This phase took 6 weeks, during 13 August–24 September 2019.
Independent observers
During this part of the study, the rangers carried out searches as they normally would, but two volunteers from a local non-profit organization were asked to join them as independent observers. The observers had little or no ex- perience with such searches, and their role was simply to join the rangers and look for evidence of poaching activities. Although using law enforcement supervisors would have been more realistic than using volunteers, this would have also distracted supervisors from their daily duties and re- sponsibilities. The observers were told not to interfere with the team’s decision-making, but were free to interact with the rangers and ask them
questions.Various people in- cluding volunteers, researchers and journalists have joined the rangers on their patrols in the past and the daily patrol operations did not change. The ranger teams were again not informed about the research. This phase took place in October 2019 and lasted for 5 weeks.
Systematic search patterns
We examined two different search patterns: parallel lines (Fig. 1a) and a quadrant search pattern (Fig. 1b). The parallel lines were c. 10–20mapart, depending on the environment, and were usually walked in a north–south direction. The quadrant pattern was inspired by a previous survey for snares (Watson et al., 2013), in which the search was con- ducted along the edges and corners of two squares: an outer (350 × 350 m) and inner quadrant (175 × 175 m). The team searched from corner to corner of the outer quadrant first, followed by the inner quadrant. At every corner the team stopped and split up for 5 minutes, searching for snares in the vicinity. The teams responsible for walking the systematic search
patterns consisted of four people. Three people were tasked with searching for snares. They walked at a distance of c. 10m from each other, which allowed them to remain in visual contact (a standard security protocol in areas with poten- tially dangerous wildlife) and reduced the likelihood that an imitation snare would be missed (Wato et al., 2006). The fourth person made sure that, as far as reasonably possible, the others maintained their positions. Every imitation snare detected during the searches was removed and the location recorded using a GPS. These searches took c. 2.5 hours, simi- lar to a regular search. The search teams comprised volun- teers and researchers from a local NGO instead of rangers. Although involving rangers would have been more realistic,
FIG. 1 Two systematic search patters: (a) parallel lines, and (b) quadrant pattern, in which a 5-minute search was conducted in every corner of the two quadrants.
it would have disrupted their normal operations. The volun- teers had little or no experience with snare searches, but were informed about the research design and how to look for imitation snares. The systematic searches were carried out during 5 July–18 August and 23 September–30 October 2019. Systematic searches took place during the same peri- ods as the spatially focused patrols and patrols with inde- pendent observers, but never on the same day.
Survival analysis
We used the Kaplan–Meier estimator to describe the over- all probability of imitation snares remaining undetected over the study period (Kaplan & Meier, 1958; Klein & Moeschberger, 2003). We generated a Kaplan–Meier sur- vival curve by pooling all data from the four search strate- gies, to visualize when imitation snares were reported. Because the number of detected snares was low, we could not estimate a survival curve for every search strategy. The start time was set as 5 April 2019, the day after the last imi- tation snares were deployed. The end time was the date of detection or when the imitation snare was removed at the end of the study. We used the packages survival and surv- miner (Therneau, 2015; Kassambara et al., 2019)in R 3.5.2 (R Core Team, 2018) for the survival analyses.
Bootstrap sampling
To estimate the number of imitation snares that were likely to be detected by a patrolling team, we used a 10 m buffer around the GPS routes of the snare searches. The width of the buffer was based on the distance at which an imitation snare can be seen and the accuracy of GPS fixes. We con- sidered all imitation snares within the buffer available for detection, and calculated the number of imitation snares available for detection for each search.Weused the same ap- proach for the systematic search patterns. We used the GPS data of the snare searches to calculate the duration of the
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
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