We recently came across a new and very cool piece of research which investigated the effectiveness of conventional trial cameras for detecting various North American mammals. To conserve power, trail cameras stay asleep most of the time and use a basic motion sensor to wake the camera up to take photos. To test how many animals were missed by the motion sensor they configured the cameras to take a photo every minute and also whenever the motion sensor detected triggered. The researchers then went through 1.5 million photos taken in a variety of environments and worked out how many times there was an animal on the timed photo vs the motion triggered photos. Unsurprisingly, the research showed that the motion sensors worked well for large animals and very poorly for small animals.
Here's a summary of the results:
The way to read this summary is that about 80% of the bears, wolves and bobcats were detected via the motion sensor compared to only 10-20% of smaller mammals. For the even smaller and faster-moving animals of interest in New Zealand, such as rats and stoats, detection rates will be even lower. This research confirms the Cacophony Project's own research using sensitive thermal cameras - trail cameras as just not very sensitive for small animals.
This paper also contains lots of good information about how trail cameras motion sensors seem to be affected by vegetation, weather and other conditions.
See full paper in the Wildlife Society Bulletin (Urbanek R, Ferreira H, Olfenbuttel C, Dukes C, & Albers G. See What You’ve Been Missing: An Assessment of Reconyx® PC900 Hyperfire Cameras. Wildlife Society Bulletin. https://wildlife.onlinelibrary.wiley.com/doi/abs/10.1002/wsb.1015).