DOI: 10.5061/dryad.p8cz8w9m2
title: An empirical evaluation of camera trap study design: how many, how long, and when?

description: 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 locations were
 needed for precise estimates of species richness, depending on scale of
 the study. The precision of species-level estimates of occupancy was
 highly sensitive to occupancy level, with &lt;20 camera sites needed
 for precise estimates of common (&gt;0.75) species, but more than 150
 sites likely needed for rare (&lt;0.25) species. Species detection
 rates were more difficult to estimate precisely at the grid level due to
 spatial heterogeneity, presumably driven by unaccounted for habitat
 variability 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 had strong impacts on mammal
 communities in both tropical and temperate sites.
description: We used camera trap data already available through repositories
 or collaborators. Most data came from the eMammal or TEAM repositories. 
 We also used one data set (China) from collaborators that was not already
 archived.  All camera traps were set similarly, in
 being placed on a tree at 0.5m facing parallel to the ground, with no
 bait.  A variety of camera models were used, but all had infrared flashes
 and fast (&lt;0.5s) trigger times. Camera trap designs were either
 regular (grid) or stratified random. 
description: For this paper we wanted to asess the importance of three things
 to camera trap study design: amount of locations surveyed (spatial),
 amount of time each survey ran (temporal), and rather season mattered
 (seasonal).  We broke into three teams to analyze these data, and used
 three slightly different collections of data for each team.  Thus, you
 will find three datasets labeled as to which analyses they were part of:
 spatial, temporal, or seasonal.  All data is presented
 as raw detection data, giving the date, time, and species for each time
 photograph was recorded.  These are organized as 'deployments'
 representing a time period a camera was placed in a given
 location.   We are including a TXT file with the Data
 Dictionary from eMammal that describes all the standard fields.  A few
 files have additional fields we added that should be self
 explanatory.