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vegetation cover. Future research could build upon the de- sign of our field experiment and test how vegetation density influences detection probability. The rangers were not informed about our study, tomin-
imize any impact on their behaviour. However, it became apparent in October 2019 that the rangers were aware of the study and the imitation snares, possibly through infor- mation provided by a volunteer who joined one of the snare searches in early August. We examined the patrol effort around that time and found a small increase in hours and distance patrolled, potentially a result of rangers wanting to find snares to receive the financial reward. No imitation or real snares were detected for the next 2 weeks, after which patrol efforts decreased to similar levels as observed in June and July 2019. Another limitationwas that different peoplewere involved
in the different searches.We used volunteers to walk the sys- tematic patterns because involving rangers would have dis- rupted their normal operations. Although it is unexpected that volunteers would be better at detecting snares than ran- gers (Lewandowski & Specht, 2015), a potential explanation could be that the searches were a novel experience for the volunteers. Many of the volunteers were highly motivated, enjoyed walking outside and specifically visited the Reserve to gain experience. The rangers, in contrast, are accustomed to patrol activities and searches for snares. Although they are more experienced than the volunteers, searching for snares is a routine activity for them. This may have contributed to the differences in the detection rate.
Interpretation of findings
The detection probability of the systematic searches was c. twice as high as the baseline estimate. This could not be attributed to differences in patrolling effort because the time spent patrolling and the area coveredwas generally the same among the different patrol strategies. A potential expla- nation for why the systematic searches outperformed the other strategies could lie in differences in how patrol effort was distributed across an area. By systematically searching an area, patrol effort is more concentrated, whereas it is more diffused with the other patrol strategies. The trade-off is that it takes more time to cover the same area. A hybrid model in which systematic searches are combined with regular snare searches could offer a practical compromise. For example, a ranger team could start patrolling as normal, until the first snare or sign of illegal activity is found. The team could then switch to a systematic strategy to search the area for more signs. This approach assumes that poach- ers tend to set their snares in clusters, rather than distribut- ing them evenly (Kimanzi et al., 2014; Risdianto et al., 2016). Implementing a systematic approach may require addition- al resources initially to appropriately adjust existing law
enforcement operations. For example, supervisors could pro- vide additional training or join the rangers on their patrols to ensure that the strategy is implemented properly. The context of our research was searching for snares in a
semi-arid environment. Although systematic searches out- performed other strategies, this does not necessarily imply that our findings are applicable in other environments or for other forms of poaching. O’Kelly et al. (2018) related the higher detectability of snares in an evergreen forest to the difficult terrain and fewer existing trails. In such en- vironments, a suitable approach could involve systematic searches along trails. The search pattern may vary depend- ing on the context, but more systematic snare searches could be a practical alternative to standard searches. Hence, al- though the findings of our study are not necessarily gen- eralizable, our method for testing and evaluating patrol strategies could be used in different environments or for other types of poaching.
Future research
The method outlined here could form the basis of larger-scale experiments in other areas and for other patrol strategies. Many law enforcement interventions are not de- signed in a way that facilitates evaluation (Baylis et al., 2016; Kurland et al., 2017). Aside from testing the effectiveness of an intervention, evaluations should also consider the mech- anisms, moderators, implementation and financial impli- cations of such interventions (Johnson et al., 2015). This is challenging, but guidelines such as those of the Centre of Evidence-Based Conservation (CEE, 2013) can facilitate the examination of poaching problems and the development of prevention strategies. For example, in South Africa, patrol strategies for rhinoceros poaching could be tested. Many protected areas have rangers stationed at outposts to listen for gunshots. A relatively simple experiment could deter- mine the optimal and least suitable conditions for detecting gunshots, and how these affect the accuracy of observations. Further studies of the probabilities of detecting snares
could incorporate landscape features such as terrain and vegetation, which can be derived from satellite imagery. Such studies have been conducted in tropical forests (O’Kelly et al., 2018; Ibbett et al., 2020), but not in semi-arid landscapes (Rija, 2017). Analysing how landscape features influence detection probability could help identify the best patrol strategy in a particular environment. Landscape fea- tures may also be predictive of where rangers will patrol, or where poachers may be active.
Conclusion
Our study provides baseline data for the probability of de- tecting snares used for poaching in a semi-arid landscape,
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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