ABSTRACT
1. Camera traps deployed in grids or stratified random designs are a well-established survey tool for
wildlife but there has been little evaluation of study design parameters.
2. We used an empirical subsampling approach involving 2225 camera deployments run at 41 study
areas around the world to evaluate three aspects of camera trap study design (number of sites,
duration and season of sampling) and their influence on the estimation of three ecological metrics
(species richness, occupancy, detection rate) for mammals.
3. We found that 25-35 camera sites were needed for precise estimates of species richness,
depending on scale of the study. The precision of species-level estimates of occupancy () washighly sensitive to occupancy level, with <20 camera sites needed for precise estimates of
common (>0.75) species, but more than 150 camera sites likely needed for rare (<0.25)
species. Species detection rates were more difficult to estimate precisely at the grid level due to
spatial heterogeneity, presumably driven by unaccounted habitat variability factors within the
study area. Running a camera at a site for 2 weeks was most efficient for detecting new species,
but 3-4 weeks were needed for precise estimates of local detection rate, with no gains in precision
observed after 1 month. Metrics for all mammal communities were sensitive to seasonality, with
37-50% of the species at the sites we examined fluctuating significantly in their occupancy or
detection rates over the year. This effect was more pronounced in temperate sites, where
seasonally sensitive species varied in relative abundance by an average factor of 4-5, and some
species were completely absent in one season due to hibernation or migration.
4. We recommend the following guidelines to efficiently obtain precise estimates of species
richness, occupancy and detection rates with camera trap arrays: run each camera for 3-5 weeks
across 40-60 sites per array. We recommend comparisons of detection rates be model-based and
include local covariates to help account for small-scale variation. Furthermore, comparisons
across study areas or times must account for seasonality, which could have strong impacts on
mammal communities in both tropical and temperate sites.