Sooner, closer, or longer: detectability of mesocarnivores at camera traps

Abstract

Camera trapping, paired with analytical methods for estimating species occurrence, population size or density, can yield information with direct consequences for wildlife management and conservation. Detectability, the ability to detect a species or individual if it is present, affects the reliability and efficiency of camera trap surveys and, in turn, varies across species, space and time. Greater detectability means greater sample size, and a common approach to boost detectability of wildlife by camera traps involves the application of olfactory lures. Using a camera trap study on sympatric mesocarnivores (European badger Meles meles, red fox Vulpes vulpes, pine marten Martes martes and domestic cat Felis catus), we quantified three elements of detectability: (1) the time until first detection ('sooner', conditional on being present), (2) the proximity to a focal point in front of the camera ('closer', conditional on being detected) and (3) the duration of exposure to the camera ('longer', conditional on being detected). A hierarchical analytical approach and a quasi-experimental setup allowed us to test for and quantify the species-specific effect of olfactory lures on these aspects of detectability. Depending on species, average median time to first detection ranged from 4 to 28 days, distance to the focal point from 0.3 to 0.8 body lengths, and median time to departure from 2 to 6 seconds. Credible intervals overlapped substantially between most species in all three measures, and variation between observations was extensive. We detected effects of lures on time to first detection for cats (castoreum; American beaver Castor canadensis scent), distance to focal point for badgers (striped skunk Mephitis mephitis scent) and martens (castoreum, fox and skunk scents), and the duration of exposure for foxes (fox and skunk scents). We discuss how a multifaceted perspective on detectability in camera trap studies, linked with species biology, can give investigators a more structured approach to selecting and testing measures intended to boost detection probability.

Consequences of ignoring variable and spatially-autocorrelated detection probability in spatial capture-recapture

“…Observed and unobserved spatially-autocorrelated variation in detection probability could have many causes (Gaspard et al 2019), divided into two broad categories. On the one hand is the nature of the data collection; for example, regional differences in the mobilization of volunteers for non-invasive DNA collections, variation in camera trap efficiency due to inadvertent scent contamination at a cluster of sites, or reduced physical capture success in traps installed by a less-experienced operator in their designated area (Kristensen and Kovach 2018; Bischof et al 2020a; Tourani et al 2020a). On the other hand are characteristics of the study species and its environment, such as spatial gradients or clusters in site utilization (not density) or spatial variation in behavior (e.g.…”

Olfactory lures in predator control do not increase predation risk to birds in areas of conservation concern

“…BTS use a combination of visual and chemical prey cues in foraging (Chiszar et al 1988;Smith et al 1988). Other olfactory predators are first drawn in by scent and upon approach use vision to assess the lure (Tourani et al 2020). Because snakes swallow their prey whole, prey size may be evaluated before ingestion (Radcliffe et al 1980;Shine et al 1998;Glaudas et al Guam National Wildlife Refuge.…”

Modelos de ocupación para datos de cámaras trampa

“…El objetivo de un diseño de muestreo que busque generar estimaciones de la ocupación debe centrarse en maximizar la detección de la especie objetivo y captar la mayor información posible sin violar los supuestos del modelo (Hamel et al 2013;Shannon et al 2014;Tourani et al 2020).…”