How do passive infrared triggered camera traps operate and why does it matter? Breaking down common misconceptions

Abstract

The use of passive infrared (PIR) triggered camera traps has dramatically increased in recent decades. Unfortunately, technical descriptions of how PIR triggered camera traps operate have not been sufficiently clear. Descriptions have often been ambiguous or misleading and in several cases are demonstrably wrong. Such descriptions have led to erroneous interpretations of camera trapping data. This short communication clarifies how PIR sensors operate. We clarify how infrared radiation is emitted and transmitted, and we describe the parts of the PIR sensor and how they detect infrared radiation and, by extension, fauna. Several problematic descriptions of PIR sensors are drawn on to highlight flawed descriptions and demonstrate where erroneous interpretations of camera trapping data occurred. By clarifying the language and the description of PIR triggered camera traps, this paper ensures that wildlife researchers and managers using camera traps will avoid flawed interpretations of their data. Avoiding flawed interpretations of data should reduce wasted effort and resources that would otherwise come about as researchers attempt to test flawed hypotheses. Furthermore, this paper provides a thorough technical reference for camera trapping practitioners, which is not present elsewhere in the wildlife research literature.

Single-Camera Trap Survey Designs Miss Detections: Impacts on Estimates of Occupancy and Community Metrics

“…Three site were removed because they were placed in human development and outside of forested habitat, reducing the total number of sampled camera-sites to 20. At each camera-site we deployed four digital remote camera traps (Cuddeback E2 [20.0 megapixel], Attack IR [5.0 megapixel], or Ambush IR [5.0 megapixel], Non Typical, Inc., Park Falls, WI) which were furnished with passive infrared sensors that trigger the camera when a rapid change is detected in the surface temperature of an object [32], and were equipped with incandescent flash illumination to assist in species identification at night. Additionally, all camera traps used were furnished with one-fourth second trigger speeds and were capable of a flash range of at least 30 m. The four cameras were deployed on the same tree bole with even spacing among the cameras so as to have ~90° spacing between cameras (Fig 1C).…”

The wild life of tick-borne pathogens

“…In my case this meant that camera traps would start to take photographs as soon as a warm-blooded animal walked past and was detected by the PIR sensor 53 . The sensitivity of the PIR sensor is, among other things, dependent on the surface temperature of the animal walking past, which is different for animals of different sizes, as bigger species omit more heat than smaller species 54 .…”

WiseEye: Next Generation Expandable and Programmable Camera Trap Platform for Wildlife Research

“…A PIR sensor relies on detecting both a ‘heat signature’–thermal difference between the animal and the ambient background temperature—and movement [5,19]. Detecting animal presence is the critical function of a camera trap.…”