Effective sociodemographic population assessment of elusive species in ecology and conservation management

Abstract

Wildlife managers are urgently searching for improved sociodemographic population assessment methods to evaluate the effectiveness of implemented conservation activities. These need to be inexpensive, appropriate for a wide spectrum of species and straightforward to apply by local staff members with minimal training. Furthermore, conservation management would benefit from single approaches which cover many aspects of population assessment beyond only density estimates, to include for instance social and demographic structure, movement patterns, or species interactions. Remote camera traps have traditionally been used to measure species richness. Currently, there is a rapid move toward using remote camera trapping in density estimation, community ecology, and conservation management. Here, we demonstrate such comprehensive population assessment by linking remote video trapping, spatially explicit capture–recapture (SECR) techniques, and other methods. We apply it to three species: chimpanzees Pan troglodytes troglodytes, gorillas Gorilla gorilla gorilla, and forest elephants Loxodonta cyclotis in Loango National Park, Gabon. All three species exhibited considerable heterogeneity in capture probability at the sex or group level and density was estimated at 1.72, 1.2, and 1.37 individuals per km2 and male to female sex ratios were 1:2.1, 1:3.2, and 1:2 for chimpanzees, gorillas, and elephants, respectively. Association patterns revealed four, eight, and 18 independent social groups of chimpanzees, gorillas, and elephants, respectively: key information for both conservation management and studies on the species' ecology. Additionally, there was evidence of resident and nonresident elephants within the study area and intersexual variation in home range size among elephants but not chimpanzees. Our study highlights the potential of combining camera trapping and SECR methods in conducting detailed population assessments that go far beyond documenting species diversity patterns or estimating single species population size. Our study design is widely applicable to other species and spatial scales, and moderately trained staff members can collect and process the required data. Furthermore, assessments using the same method can be extended to include several other ecological, behavioral, and demographic aspects: fission and fusion dynamics and intergroup transfers, birth and mortality rates, species interactions, and ranging patterns.

Towards Automated Visual Monitoring of Individual Gorillas in the Wild

“…Remote camera trapping can effectively record all apes in a given region [35]. It effectively bypasses common sources of error in traditional survey methods [35,58,23] and is not restricted to a singular species nor research question.…”

“…It has great potential to provide unique and valuable data on the impacts of conservation threats [71], sociodemographics [23], behavioural plasticity [32,55,3], disease mapping and screening [9], species interactions [23], habitat use [53,24], feeding ecology [24,51,59], activity patterns [32,55], and ranging patterns [48].…”

“…In addition, animal transfers between groups can currently only be estimated with an accuracy that ranges from just a few days up to years [5,57,6]. Automatic monitoring with camera traps in the wider geographical area surrounding Mbeli Bai could help to improve the accuracy of the socio-demographic data [23], and improve our understanding the extent and variation of dispersal patterns and group dynamics [2,23,17].…”

“…The long-term data on the demographics and group structure of dozens of known gorilla units from Mbeli Bai could form a unique and novel combination with spatially-explicit capture-recapture data that, when combined, could tackle a myriad of socioecological questions (e.g. ranging patterns, habitat use, seasonal activity patterns, disease screening) as well as population estimates for the wider area, potentially at a park-wide or landscape level [35,53,23,24].…”

An automated chimpanzee identification system using face detection and recognition

“…Thus, the system will assist biologists, researchers, and gamekeepers with tedious annotation work of gathered image and video material and therefore has the potential to open up new venues for efficient and innovative wildlife monitoring and biodiversity conservation management. Currently, intensive pilot studies using autonomous infrared-triggered remote video cameras are conducted in Loango National Park, Gabon [48] and Taï National Park, Côte d'Ivoire [49]. These studies have provided promising results in both number of species detected, as well as visitation rates, demonstrating the potential of such an approach for biomonitoring.…”