Camera traps are increasingly used to study animal behaviour and are seen as a non-invasive alternative to other methods (e.g. telemetry). However, recent studies have shown that animals do notice and react to camera traps. For example, mechanical sounds produced by the cameras when triggered as well as the camera's flash type could affect animal behaviour. To quantify the extent to which different flash types affect animal behaviour, Maik Henrich and colleagues from the University of Freiburg, Germany measured responses of roe deer and red deer to standard infrared flash and to black flash of camera traps in the Czech Republic. Overall, responses to the cameras varied between species, as red deer were more likely to flee upon noticing the cameras than roe deer, though the likelihood of these flight responses decreased over time. Both species reacted more to the standard infrared flash than to the black flash, which was measured as flight responses and deer looking at the cameras. Interestingly, the researchers found variation in reactions to flash between their two forest study areas, which they suggest could be due to differences in hunting pressure between areas. They conclude by recommending that for studies where behavioural responses are of interest, cameras with black flash be used and also that cameras should be placed at least 5 m or more from game trails to avoid affecting behaviour.
Their study, "The influence of camera trap flash type on the behavioural reactions and trapping rates of red deer and roe deer" was published in Remote Sensing in Ecology and Conservation and can be found here.