Scent Lure Effect on Camera-Trap Based Leopard Density Estimates

Abstract

Density estimates for large carnivores derived from camera surveys often have wide confidence intervals due to low detection rates. Such estimates are of limited value to authorities, which require precise population estimates to inform conservation strategies. Using lures can potentially increase detection, improving the precision of estimates. However, by altering the spatio-temporal patterning of individuals across the camera array, lures may violate closure, a fundamental assumption of capture-recapture. Here, we test the effect of scent lures on the precision and veracity of density estimates derived from camera-trap surveys of a protected African leopard population. We undertook two surveys (a ‘control’ and ‘treatment’ survey) on Phinda Game Reserve, South Africa. Survey design remained consistent except a scent lure was applied at camera-trap stations during the treatment survey. Lures did not affect the maximum movement distances (p = 0.96) or temporal activity of female (p = 0.12) or male leopards (p = 0.79), and the assumption of geographic closure was met for both surveys (p >0.05). The numbers of photographic captures were also similar for control and treatment surveys (p = 0.90). Accordingly, density estimates were comparable between surveys (although estimates derived using non-spatial methods (7.28–9.28 leopards/100km2) were considerably higher than estimates from spatially-explicit methods (3.40–3.65 leopards/100km2). The precision of estimates from the control and treatment surveys, were also comparable and this applied to both non-spatial and spatial methods of estimation. Our findings suggest that at least in the context of leopard research in productive habitats, the use of lures is not warranted.

The influence of movement on the occupancy–density relationship at small spatial scales

“…, Braczkowski et al. ). We discretized the State Space using a 500 × 500 m (0.25 km 2 ) grid that defined the possible locations of all activity centers (Braczkowski et al.…”

“…We discretized the State Space using a 500 × 500 m (0.25 km 2 ) grid that defined the possible locations of all activity centers (Braczkowski et al. , Williams et al. ), excluding cells that were predominantly water or urban land use (ESA ).…”

Competition and specialization in an African forest carnivore community

“…We can use occupancy modeling to gain insight into mechanisms of niche specialization between closely related species (limiting similarity) or through ecological mechanisms (interference competition; Table 1). Single-species occupancy modeling has become an important tool for identifying influential biotic and abiotic factors contributing to species presence and persistence in a given ecosystem (Braczkowski et al, 2016;MacKenzie et al, 2006;Steenweg et al, 2016). Two-species occupancy modeling assists in the study of resource partitioning influenced by competition (MacKenzie, Bailey, & Nichols, 2004;MacKenzie et al, 2006;Richmond, Hines, & Beissinger, 2010).…”

Single-Camera Trap Survey Designs Miss Detections: Impacts on Estimates of Occupancy and Community Metrics

“…Recent areas of research utilizing camera traps include studies of species distribution [3], community dynamics [4], population densities [5], and occupancy modeling [6–7]. Noteworthy increases in camera trap deployment [8], however, have prompted investigation into camera trap survey design to address the sometimes low detection rates associated with this survey method [9]. Deploying attractants at a camera-site has been used to increase detection rates [10], although this technique can affect which species or functional groups are detected at a camera-site [2].…”