To test the hypothesis that rangers were more likely to detect snares in PAs where there was high investment in law enforcement (i.e. more rangers per unit area and more resources: vehicle, fuel, etc) and the ecological factors driving snare detection, I simulated poaching by setting dummy snares (see below for a description) in the Serengeti National Park and the two game reserves. In each management zone, I aimed to set at least 30 groups of snares in locations typical of actual poacher activities, accessing locations in all regions of each zone by vehicle or on foot. To site dummy snares effectively, we used experience of how poachers set snares gained over from initial surveys in 2015 (during which 340 snares were located; Rija et al. in prep) and from 3.5 years working as a ranger. I set a total of 2316 dummy snares, distributed across 309 separate locations (sites). The dummy snare made of an easy-to break plastic
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material (hence cannot catch or cause harm to animals), looks very similar to most real wire snares used by poachers in these protected areas (Figure 4. 1). Since poachers typically set groups of snares, we set a random number of between 4 and 20 snares at each of the 309 locations used. Each snare within a group was < 200 m from another snare, and each site within a zone was separated by at least 2 km from the next site (Figure 4. 2). We used local habitat characteristics, such as available water pools, abundant green grasses, available ungulates; animal trails etc. to select sites to locate dummy snares. These habitat features have significant correlations with the distribution of illegal activities in the Serengeti ecosystem (Chapter 3) and are frequently used by rangers as cues for detailed searches for signs of poaching (Walsh & White, 1999). Overall, the dummy snare experiments spanned seven management zones (Figure 4. 2); East = 415 snares (in 61 groups), North = 295 (41), South = 236 (23), Central = 376 (67), Ikorongo = 346 (45), Grumeti = 120 (11) and West = 528 (61). We fixed each dummy snare on a tree with a loop positioned mostly between paired growing trees. Whenever possible, we constructed small bush fences similar to those used by poachers (Rija pers. obs.) to guide animals through the intended paths and snare and to ensure equivalent detectability of dummy and real snares.
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Figure 4. 1. Photographs of real poacher snare (A) and a dummy snare (B) used in poaching simulation experiment to understand ranger detection efficiency in the Serengeti ecosystem. Photograph courtesy by SCCri team 2015/2016.
To test the hypothesis that habitat structures (e.g. available water pools, bushes, animal tracks etc.) and characteristics (e.g. herb height, tree height etc.) influence detection of the dummy snares, we recorded the exact GPS coordinates of each snare set, as well as its proximity to the nearest snare, and the number of trees, bushes and animal trails within a radius of 20 m of the snare. Available water pools (within visible distance from set dummy snares) and whether the snare was set on an animal trail was recorded. We also measured the ground cover, herb height, and tree height within a radius 20 m of the snare as these characteristics have been shown to significantly influence the distribution of wire snares in Serengeti (Chapter 3). I expected these to influence snare detection by the rangers. I also separated ‘trees’ into those that were single or paired, but these numbers were highly correlated with tree number (r >0.5), so I used tree number in subsequent analysis.
A
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Figure 4. 2. Location of the three protected areas in Serengeti Ecosystem (Serengeti National Park and Grumeti and Ikorongo Game Reserves) in Tanzania and the spatial distribution of the dummy snare experiments across different management zones. There was low snare detection by the rangers during the three months of field testing.
To estimate the daily detection rate of snares and the mortality risks posed to the animals, we left the snares in the field for a period of up to twelve weeks (range 30-84 days) before returning to remove unfound snares, recording the length of time each snare was in the field and undetected. Throughout this period, we recorded the recovery of dummy snares by the rangers, who had been requested to remove every dummy snare they encountered during routine patrols. For each ranger-recovered snare, we recorded the date recovered. To minimize errors resulting from the rangers being informed of the location of the dummy snares, we set dummy snares without ranger presence, but
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rangers were informed of the experiment when the snaring within a particular management zone was completed. Our discussions with rangers during field work showed they were positive about these experiments and rangers were honest to report that they did or did not detect any dummy snare or simply they did not perform any patrols (e.g. in East and Central zones of Serengeti National Park) due to resource limitations. This suggests that ranger effort may have not been particularly biased by their perception of these experiments, though we acknowledge the possibility.
To assess species mortality risks from wire snares, we recorded the status of each snare during removal. If the snare was intact and undisturbed we assumed that no animals would have been captured, but if the snare loop was broken open and confirmed the cause to be an animal walked into it, we assumed a capture would have been made. In reality, not all disturbed snares will result in capture, so our estimates of capture rates could be biased upwards. At disturbed snares, we recorded the species that would have been captured, based on fresh or recent signs at the location, such as animal
dung/pellets, spoor and hairs of animals.