Validating camera trap distance sampling for chimpanzees

Abstract

The extension of distance sampling methods to accommodate observations from camera traps has recently enhanced the potential to remotely monitor multiple species without the need of additional data collection (sign production and decay rates) or individual identification. However, the method requires that the proportion of time is quantifiable when animals can be detected by the cameras. This can be problematic, for instance, when animals spend time above the ground, which is the case for most primates. In this study, we aimed to validate camera trap distance sampling (CTDS) for the semiarboreal western chimpanzee (Pan troglodytes verus) in Taï National Park, Côte d'Ivoire by estimating abundance of a population of known size and comparing estimates to those from other commonly applied methods. We estimated chimpanzee abundance using CTDS and accounted for limited availability for detection (semiarboreal). We evaluated bias and precision of estimates, as well as costs and efforts required to obtain them, and compared them to those from spatially explicit capture‐recapture (SECR) and line transect nest surveys. Abundance estimates obtained by CTDS and SECR produced a similar negligible bias, but CTDS yielded a larger coefficient of variation (CV = 39.70% for CTDS vs. 1%/19% for SECR). Line transects generated the most biased abundance estimates but yielded a better coefficient of variation (27.40–27.85%) than CTDS. Camera trap surveys were twice more costly than line transects because of the initial cost of cameras, while line transects surveys required more than twice as much time in the field. This study demonstrates the potential to obtain unbiased estimates of the abundance of semiarboreal species like chimpanzees by CTDS.HIGHLIGHTS Camera trap distance sampling produced accurate density estimates for semiarboreal chimpanzees. Availability for detection must be accounted for and can be derived from the activity pattern.

Drawn out of the shadows: Surveying secretive forest species with camera trap distance sampling

“…Except for the endemic Congo peafowl, all chosen species were mammals. Table 2 shows species-specific information obtained from CTs, including activity times, availability according to Cappelle et al (2019) and Rowcliffe et al (2014;examples provided in Figure 2), as well as truncation distance. Detectability positively correlated with body size, with small-sized species being undetected within the first 2 m from the camera (Figure 3).…”

“…Although differences in the specific availability calculated according to Cappelle et al (2019), and Rowcliffe et al (2014) were minor with large sample sizes, ARo presented major advantages: (a) calculations provided standard errors of estimated availabilities (that F I G U R E 5 Relative species-specific concordance of density estimates corrected with ARo (Rowcliffe et al, 2014) and ACa (Cappelle et al, 2019) could be included in the estimation of total variance of density) and (b) values appeared to be less influenced by the peak of observation and stochasticity ( Figure 2; Table 3). Both methods rely on the assumption that at peak time, 100% of the population is available for detection (Rowcliffe et al, 2014), with asynchronous activity patterns of individuals within species leading to an overestimation of activity time, hence underestimated densities.…”

“…Reactivity to the camera is known to bias density estimates, as it violates the assumptions of DS (Buckland et al, 2001). Attraction to CTs, providing a high number of observations close to the camera has been previously addressed with left-truncation (Cappelle et al, 2019).…”

“…biomonitoring, camera trap, cryptic species, density estimation, distance sampling, multispecies, Salonga National Park, unmarked population wild populations of Maxwell's duiker Philantomba maxwellii (Howe et al, 2017), and Western chimpanzees Pan troglodytes verus in Taï National Park, Côte d'Ivoire (Cappelle et al, 2019) returning unbiased estimates for the latter. In addition, by using a DS approach, CTDS takes advantage of a consolidated mathematical framework, open-source software and a vast community of users and developers, making the method easily accessible.…”

Listening and watching: Do camera traps or acoustic sensors more efficiently detect wild chimpanzees in an open habitat?

“…Seasonality influences activity patterns, ranging and feeding behaviour of chimpanzees (Doran, ), and may consequently influence chimpanzee detectability with CT and PAM. CT studies on chimpanzees have been conducted to study uncommon behaviour, for example stone throwing (Kühl et al, ) and crab hunting (Koops et al, ), but also for abundance and density estimation (Cappelle, Després‐Einspenner, Howe, Boesch, & Kühl, ; Després‐Einspenner, Howe, Drapeau, & Kühl, ) among others. Only a few studies have employed PAM with chimpanzees; those have focused on group ranging and territory use (Kalan et al, , ) and temporal patterns of vocalizations (Piel, ).…”