Detecting wildlife poaching 573
deployment of law enforcement resources (Gavin et al., 2010; Keane et al., 2011). Most studies of poaching acknowledge the challenges of
detecting poaching events (Wato et al., 2006; Gavin et al., 2010; Becker et al., 2013; Watson et al., 2013), but few have estimated detection probabilities or explored strategies that could lead to increased performance. Recent patrol deployment research and mark–recapture models have focused on predicting the levels of poaching activities in unpatrolled or infrequently patrolled areas, through math- ematical modelling (Critchlow et al., 2015; Linkie et al., 2015; Fang et al., 2017; Moore et al., 2017). These models can overcome some of the potential biases, but only under the assumption that the recorded data are representative of all poaching activities. This assumption, however, cannot be tested using only recorded poaching data. This makes it difficult to estimate poaching trends and the impact of law enforcement strategies on poaching behaviour. Therefore, there is a need for exploration and comparison of different patrol strategies (Baylis et al., 2016). An evaluation of new strategies or technologies is chal-
lenging if the extent of the problem is unknown, but field experiments can help evaluate the context, mechanisms and outcomes of an intervention (Johnson et al., 2015; Jones, 2018). A few studies have designed such experiments to examine the probabilities of detecting poaching (Rija, 2017;O’Kelly et al., 2018; Ibbett et al., 2020). They found that the detectability of snares is influenced by habitat type, level of experience of patrol staff, and search effort. It is still unknown, however, how different patrol strategies could potentially increase detection. Here, we outline a method for estimating the probabil-
ities of detecting wildlife poaching. We estimated the detec- tion probability of the current patrol strategy used in a protected area, and compared it against alternative patrol strategies. We focused on snaring because the use of wire snares is a popular and widespread hunting technique (Lindsey et al., 2013; Gray et al., 2018) and has been the focus of recent research (Rija, 2017;O’Kelly et al., 2018; Ibbett et al., 2020). We tested different patrol strategies in a field experiment with a known number and spatial distri- bution of imitation snares. In preparation for the field experiment we identified
strategies that could potentially increase the probability of detecting snares, and determined appropriate outcome mea- sures for the comparison and evaluation of those strategies. There are a number of potential patrol strategies that could be examined, but we focused on three strategies that re- quired minimal or no changes to current law enforcement operations: spatially focused patrols, independent observers and systematic search patterns. Spatially focused patrols search for signs of poaching at a
specific location at the micro-level; e.g. around a water hole. This is different from most law enforcement operations;
rangers are typically tasked with searching a particular grid cell $1 km2. A spatially focused patrol could be used in situations where law enforcement officials have received information about the precise location of a particular poach- ing activity, for example because a poacher was recently observed there, or through local informant networks (Linkie et al., 2015). Such information can help law enforcement managers with directing resources towards high-risk areas, and potentially increase the detection rate of poaching. We therefore hypothesized that spatially focused patrols have a higher probability of detecting snares compared to the baseline detection probability. Studies of industrial psychology have shown that ob-
served individuals who perform a specific task may behave differently because they know that they are being watched. This is known as reactivity (Harvey et al., 2009), and can enhance performance, industrial productivity and health- related behaviours (Usichenko et al., 2013; Chen et al., 2015). It has been suggested that the presence of an observer or supervisor caused urban police officers to behave more proactively (Spano, 2007; Mastrofski et al., 2010). We de- fined independent observers as non-rangers who joined the rangers on their patrol. We hypothesized that patrols accompanied by independent observers have a higher prob- ability of detecting snares compared to the baseline detec- tion probability. Systematic search strategies are rooted in modern search
theory, which was developed in the 1940s during wartime, primarily for naval use (Koopman, 1946). The theory states that searching is a probabilistic process, with no guarantee of either success or failure. However, regardless of the object of interest, a systematic search pattern is more likely to succeed than randomly moving around (Koopman, 1946; Chung & Burdick, 2007). This is especially true when the target is small, or blends with its background (Cacho et al., 2007; Delaney & Leung, 2010), which often applies to signs of poaching. Although rangers do not patrol ran- domly, a more systematic approach could yield better re- sults; e.g. a systematic walk along parallel lines or in a quadrant pattern (Chung & Burdick, 2007; Delaney & Leung, 2010). Our third hypothesis was therefore that sys- tematic search patterns have a higher probability of detect- ing snares compared to the baseline detection probability.
Study area
We conducted our study in the buffer zone of Olifants West Nature Reserve in Limpopo Province, South Africa. The cli- mate is semi-arid savannah with a mean annual rainfall of 454mm(Peel, 2014). The 4.15 km2 buffer zone is completely fenced. Rangers patrol both the main Reserve and the buffer zone, but the majority of snares have been detected in the buffer zone. In addition, the buffer zone is relatively small
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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