Table 1.
Animal characteristics 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 | |||||
| Day range | ++ | ++ | ++ | Contact with CTs | Species, season, site | (Neilson et al., 2018; Rowcliffe et al., 2008) | ||||
| Density | ++ | ++ | ++ | Contact with CTs | Species, season, site | (Neilson et al., 2018; Rowcliffe et al., 2008) | ||||
| Directionality of movementd | (−) | (−) | (−) | (−) | Contact with CTs, retention time in front of CT, and identification of detected animals | Combination with other data or (re‐)analysis of CT data | Species, season, site | None | ||
| Group sizee | (+) | (+) | (+) | (+) | Retention time in front of CT | (Re‐)analysis of CT data | Species, season, site | None | ||
| Heat signature/surface temperaturef | ++ | PIR sensor functionality | Combination with other data or (re‐)analysis of CT data | Species, season, site | (Welbourne et al., 2016) | |||||
| Home‐range size | ++ | ++ | ++ | Contact with CTs | Species, season, site | (Neilson et al., 2018; Popescu, Valpine, & Sweitzer, 2014; Sollmann et al., 2013; Steenweg et al., 2018) | ||||
| IUCN threat status/population statusg | − − | Contact with CTs | Species, site | (Brodie et al., 2015; Cove et al., 2013) | ||||||
| Niche breadthh | + | + | Contact with CTs | (Re‐)analysis of CT data | Species, season, site | (Núñez‐Regueiro et al., 2015) | ||||
| Personality/behavioral responses to CTs | +/− | +/− | Retention time in front of CT | Species, season, site | (Larrucea et al., 2007; Meek, Ballard, Fleming, & Falzon, 2016) | |||||
| Physical or geographical range of the species | ++ | Contact with CTs | Combination with other data or (re‐)analysis of CT data | Species, season, site | (McDonald et al., 2015) | |||||
| Speed of movement | − | − | Retention time in front of CT and identification of detected animals | Combination with other data | Species, season, site | (Rowcliffe et al., 2011) | ||||
| Taxonomyi | − | Identification of detected animals | Combination with other data or (re‐)analysis of CT data | Species | (Welbourne, MacGregor, Paull, & Lindenmayer, 2015) | |||||
| Territorialityj | Contact with CTs | Combination with other data or (re‐)analysis of CT data | Species, season, site | (Steenweg et al., 2018) | ||||||
| Time spend on the groundk | + | + | + | Contact with CTs and retention time in front of CT | Combination with other data or (re‐)analysis of CT data | Species, season, site | (Rovero, Martin, Rosa, Ahumada, & Spitale, 2014) | |||
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 day range.
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).
Directionality of movement can be considered at different spatial scales and is compared to a more tortuous movement. At the 3rd and 4th order an increase in directionality of the movement lowers the probability of an animal encountering a camera trap (at fixed day range). Similarly, at the 5th order an increase in directionality lowers the retention time in front of the CT (less distance is covered in front of the CT), lowering the probability of capture. At the 6th order an increase in directionality lowers the potential for multiple pictures at different angles of the same individual, reducing the probability that the individual can be identified to species or individual. Directionality of movement can differ between species and seasons, but also between sites due to differences in food availability or landscape configuration (see Table 4).
If animals move in groups, the probability that one individual triggers the CT and any individual from the group remains in the field of view of the CT increases. This is similar to an increased detection probability with group size in distance sampling (Buckland et al., 2001).
Detection probability increases with increasing difference in surface temperature of the animal versus surface temperature of the surroundings and detection probability increases with increasing surface area of the animal.
IUCN threat status is determined by a combination of the change in geographical range of a species and a change in population size of a species (IUCN, 2018). The threat status increases as geographical range and/or population size decline. Therefore, regardless of the current geographical range and population size, detection probability at the 1st order decreases with increasing threat status.
Species with a larger niche breadth have a higher probability of walking past randomly placed CTs. However, when targeting CTs for a specific species, the detection probability will be higher when the species has a smaller niche breadth, as these species can be more effectively targeted.
Detection decreases (misidentification increases) with increasing number of related species co‐occurring in the same area.
When animals use their territory exclusively, this reduces the number of individuals present in a home range and thus detection probability at the 2nd order. Territoriality can differ between species, seasons, and sites depending on species traits and resource availability.
Time spent on the ground in relation to CTs placed at ground level. This relationship is reversed when CTs are deployed somewhere else. This could be to target semi‐aquatic or semi‐arboreal species by placing CTs, respectively, above water or in the forest canopy (e.g., Bowler, Tobler, Endress, Gilmore, & Anderson, 2017; Swinnen, Hughes, & Leirs, 2015).