Background
CCTV, where you have a continuous monitoring system, can be impractical in many ecological monitoring tasks as it requires lots of power and large amounts of time to watch the footage produced. Yet CCTV can be a great way to test and see how camera-traps work (what causes them to trigger or not, and what they register on their images/footage if they do trigger). CCTV is powerful as a tool for this because it allows us to see not just what our camera-traps record, but also what they miss. And we can separate out reasons for those missed data, such as failure to trigger or else failure to register the animal after a trigger (perhaps because the animal was moving too quickly, for example). We used CCTV in this way to assess what influenced different components of detection probability separately (including trigger probability and registration probability) in our paper Findlay et al. (2020).
Another useful feature of CCTV if used at night (which matches activity of many species we monitor using camera-traps) is that the CCTV is sensitive to infra-red illumination. This means we can actually see on the CCTV the exact moment the camera-trap wakes up after being triggered. Note this is not the exact time it triggered, since there is a delay between triggering and starting to record, and it may also not be the exact time the camera-trap starts recording either, as the flash might come on momentarily before this.
Example
In the below CCTV footage, taken using a domestic CCTV system, we can see a fox cross past a camera-trap (a Bushnell HD Trophy Cam, which is set to record 10s videos). The camera-trap is in the corner of the wide gate and the hedge facing the CCTV camera we are viewing from (you’ll see it when it’s infra-red LEDs come on), facing the house. The fox comes round the large gate at about 0:17 into the video, it does a bit of a meander and then crosses in front of the camera-trap, and we see the camera-trap infra-red illumination come on at about 00:22. Note at this point (requires pausing the video) the fox’s nose is almost directly in front of the camera-trap but its body slightly to the camera-trap’s left.
If we watch the footage taken by the camera-trap at this exact trigger event (which slightly blurry due to condensation on the lens, apologies), below, and pause it in the opening frame (0:00) we can see the fox’s nose is already more than halfway across the screen, suggesting the illumination had come on slightly before recording started.
Please note, embedded YouTube videos will automatically play the next one which can cause confusion for these examples. If in doubt, you can refresh the page to get to the first (correct) video again.
Pat White | Method(Ec)ology 