The effect of camera-trap viewshed obstruction on wildlife detection: implications for inference
Remington J. Moll
A F , Waldemar Ortiz-Calo A , Jonathon D. Cepek B , Patrick D. Lorch C , Patricia M. Dennis D E , Terry Robison C and Robert A. Montgomery A
+ Author Affiliations
- Author Affiliations
A Department of Fisheries and Wildlife, Michigan State University, 480 Wilson Road, Room 13, Natural Resources Building, East Lansing, MI 48824, USA.
B Natural Resources, Cleveland Metroparks, 9485 Eastland Road, Strongsville, OH 44149, USA.
C Natural Resources, Cleveland Metroparks, 2277 West Ridgewood Drive, Parma, OH 44134, USA.
D Conservation and Science, Cleveland Metroparks Zoo, 3900 Wildlife Way, Cleveland, OH 44109, USA.
E Department of Veterinary Preventive Medicine, The Ohio State University, 1920 Coffey Road, Columbus, OH 43210, USA.
F Corresponding author. Email: rjmoll@msu.edu
Wildlife Research 47(2) 158-165 https://doi.org/10.1071/WR19004
Submitted: 11 January 2019 Accepted: 19 October 2019 Published: 10 March 2020
Abstract
Context: Camera traps are one of the most popular tools used to study wildlife worldwide. Numerous recent studies have evaluated the efficiency and effectiveness of camera traps as a research tool. Nonetheless, important aspects of camera-trap methodology remain in need of critical investigation. One such issue relates to camera-trap viewshed visibility, which is often compromised in the field by physical obstructions (e.g. trees) or topography (e.g. steep slopes). The loss of visibility due to these obstructions could affect wildlife detection rates, with associated implications for study inference and management application.
Aims: We aimed to determine the effect of camera-trap viewshed obstruction on wildlife detection rates for a suite of eight North American species that vary in terms of ecology, commonness and body size.
Methods: We deployed camera traps at 204 sites throughout an extensive semi-urban park system in Cleveland, Ohio, USA, from June to September 2016. At each site, we quantified camera-trap viewshed obstruction by using a cover-board design. We then modelled the effects of obstruction on wildlife detection rates for the eight focal species.
Key results: We found that detection rates significantly decreased with an increasing viewshed obstruction for five of the eight species, including both larger and smaller mammal species (white-tailed deer, Odocoileus virginianus, and squirrels, Sciurus sp., respectively). The number of detections per week per camera decreased two- to three-fold as visibility at a camera site decreased from completely free of obstruction to mostly obstructed.
Conclusions: These results imply that wildlife detection rates are influenced by site-level viewshed obstruction for a variety of species, and sometimes considerably so.
Implications: Researchers using camera traps should address the potential for this effect to ensure robust inference from wildlife image data. Accounting for viewshed obstruction is critical when interpreting detection rates as indices of abundance or habitat use because variation in detection rate could be an artefact of site-level viewshed obstruction rather than due to underlying ecological processes.
Additional keywords: abundance index, camera traps, study design, visibility.
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