How camera traps work and how to work them

Camera traps are very widely used to monitor the presence of animals and record their behaviour. Setting them up properly enhances their performance and data yield. The paper describes how camera traps work and gives basic advice on camera selection, setting up camera traps for various purposes, protecting them from animals, keeping them working and troubleshooting. A camera trap's capture of a still image or video is triggered by a passive infrared detector that responds when something hotter or colder than the background moves in its detection zone. Target detection is camera traps' weak point, and they need to be set up so that animals move across their detection zone rather than towards or away from the camera. Short trigger and recovery times are preferred. After dark, camera traps illuminate the subject with infrared light that is difficult for animals to see, or white light if colour images are required. During the day, stills and video are captured in colour, and at night in monochrome under infrared, or in colour with white illumination. Where cameras need to be sited depends on study design. Camera performance is sensitive to the height and angle that they are mounted at; maximum detections come from cameras just below the target's shoulder height, aimed horizontally. To avoid large numbers of false triggers, trim vegetation in the detection zone that might be moved by the wind. Keep cameras clean and change batteries frequently.