Table 2.
CT model specifications that influence detection by CTs at different orders of detection
| Characteristica | Direction and magnitude of effect on detection probability per orderb | Mechanism | Studies needed | When to correct forc | References | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | |||||
| Battery leveld | + | + | PIR sensor functionality, identification of detected animals | Design, season | (Meek & Pittet, 2012; Rovero et al., 2013) | |||||
| Battery typee | +/− | +/− | PIR sensor functionality, identification of detected animals | Design, season | (Meek & Pittet, 2012; Rovero et al., 2013) | |||||
| Camera lens focal lengthf | (−) | (+/−) | Retention time in front of CT and identification of detected animals | Application of multiple CT models | Design | (Meek & Pittet, 2012) | ||||
| Image resolution | +/− | Identification of detected animals | Design | (Meek & Pittet, 2012; Rovero et al., 2013) | ||||||
| Infrared or white flashg | 0/− | +/− | Identification of detected animals | Design, season | (Glen, Cockburn, Nichols, Ekanayake, & Warburton, 2013; Rovero et al., 2013) | |||||
| PIR sensor angleh | + | (−) | PIR sensor functionality | Design | (Meek & Pittet, 2012; Rovero et al., 2013) | |||||
| PIR sensor sensitivity | ++ | PIR sensor functionality | Design | (Meek & Pittet, 2012; Rovero et al., 2013) | ||||||
| Trigger speed of the CT | + | Identification of detected animals | Design | (Fancourt, Sweaney, & Fletcher, 2018; Meek & Pittet, 2012; Rovero et al., 2013) | ||||||
| Type of resources (video or photographs)i | + | Identification of detected animals | Design | (Meek & Pittet, 2012; Rovero et al., 2013) | ||||||
Characteristics are seen as continuous variables unless otherwise stated in the table or the footnotes, where the direction of the effect given is with an increase in the characteristic. For example, detection probability increases with an increase in trigger speed.
Direction and magnitude of effect on detection probability given in a scale from ++ to − − with 0 if no effect was found, biases given between brackets are not based on literature but estimates from the authors. When multiple studies reported contrasting results, we give the reported range separated with a /.
Factor given needs to be corrected for if multiple of these are considered in a study (see main text). Design refers to studies using a study design in which multiple CT models are used.
PIR sensor sensitivity and flash intensity decrease with battery level.
Different types of batteries (lithium, NiMH, NiZn, and alkaline) have different voltage specifications and have different discharge curves influencing PIR sensor sensitivity and potentially flash intensity over time.
The focal length of the camera lens determines the size of the field of view (a lower focal length results in a larger field of view). Therefore, we argue that a longer focal length reduces the retention time of an animal in front of the CT as the field of view is smaller. Furthermore, it could result in increased identification of species or individuals further away (as these will be larger in the frame) while at the same time it would decrease identification of animals closer to the CT as they might end up partly outside of the frame.
Many animals respond negatively to white flash (either xenon or LED) thus reducing retention time in front of the CT and the likelihood of the animal being recorded. However, if an animal is recorded, the quality of the image is often much better with white flash (best with xenon flash). Due to responses to the flash, the likelihood of obtaining multiple images is however lower, which might reduce the potential for good species or individual identification. The effect of the flash can differ between seasons due to differences in day length and the fact that the flash is only used at night.
The number of triggers of animals outside of the field of view of the camera increases with PIR sensor angle, decreasing detectability at the 6th order.
Most CTs can either take single photographs, a burst of photographs, or video. The more material is collected, going from single photographs to a burst of photographs to video, the higher the probability of species or individual identification (6th order) as behavior and multiple angles can aid identification. There is, however, a trade‐off as most CTs have a lower trigger speed when using video compared to photo mode.