Evaluating the efficacy and decay of lures for improving carnivore detections with camera traps

Abstract

Abundance and occupancy estimates are essential to wildlife research, but are often hampered by limited detections, especially for cryptic species like carnivores. While scientists can account for limited detections during statistical analyses, increasing detections in the field is the best way to reduce uncertainty. Camera traps are an effective, noninvasive method of monitoring wildlife, and using attractants with camera traps can increase the likelihood of detecting carnivores. We tested two scent lures (sardines and fatty acid tablets) against a control of no lure to determine whether either lure increased detections of six carnivore species, bobcat (Lynx rufus), coyote (Canis latrans), gray fox (Urocyon cinereoargenteus), raccoon (Procyon lotor), striped skunk (Memphitis memphitis), and ringtail (Bassariscus astutus). We also examined how detection of carnivores was affected as the lure decayed over time. We used occupancy modeling for each species to determine whether either lure increased detection probability. We then modeled how lure decay affected carnivore detections and determined the optimal length of deployment using generalized linear mixed models. Sardines increased detections across all carnivores, but also had a high rate of decay and were no different than the control at day 18. Fatty acid tablets decayed more slowly, but were not significantly different from the control at any point. Among species, detections of gray foxes and raccoons increased with both sardines and fatty acid tablets, while detections of ringtails increased only with sardines, and other species did not respond significantly to either lure. Our analysis shows that lures can increase detections of carnivores, but species‐specific responses and study objectives must be considered when choosing a lure. These results will allow future researchers to improve the accuracy of abundance and occupancy estimates through increased detections of difficult to study species which ultimately leads to better conservation and management of those species.

Effectiveness of a commercial lure to attract red fox

“…Our results suggest that the use of attractants may be of aid in wildlife ecology studies: for example, the use of attractants associated with the application of capture-recapture (Garrote et al 2012) and mark-resight (Forsyth et al 2019) could improve estimates of abundance, both because it enhances detection probability, and because longer visiting time facilitates individual recognition (Tourani et al 2020). The use of scents may also allow to improve occupancy estimation (Avrin et al 2021). Nonetheless, attractants could alter movements of animal, bringing them to areas where (Schlexer 2008;Holinda et al 2020): in turn, this could introduce sampling bias in some estimators, either for occupancy of for abundance (cf.…”

“…This may be partly explained by the possibility that kibbles, albeit pulverized, were more conspicuous than scents, and foxes tried to eat the remaining (as could be observed in some of the videos): in turn, commercial lure may arouse less interest in foxes compared to kibbles. For all treatments, visiting time in front of camera traps decreased steadily in the first 5 days after deployment, presumably due to the decay of the used essence (Avrin et al 2021). Seasonality can also impact the efficiency of the essence (Heinlein et al 2020): scent diffusion increases in hot and humid seasons, but also leads to a more rapid decay (Schlexer 2008).…”

Occupancy data improves parameter precision in spatial capture–recapture models

“…The relatively high detection rate via camera traps (0.027; SD: 0.007) is encouraging, as it suggests that obtaining suitable occupancy dataset for the integrated model should be relatively easy. The use of lures is widely used to improve the detection probability of carnivores in camera‐trapping studies (e.g., Avrin et al, 2021 ; Holinda et al, 2020 ; Iannarilli et al, 2021 ), and lure selection can significantly affect the ability to detect rare and elusive species either by making them appearing sooner, moving closer or stay longer in the cameras field of view (Ferreras et al, 2018 ; Tourani et al, 2020 ). Therefore, an appropriate selection of the most effective lures could contribute to optimizing camera‐trapping sampling protocols (Figure 4 ) and lead to better precision in SCR‐IM estimates (Gerber et al, 2011 ; Macaulay et al, 2020 ).…”

Can a mesocarnivore fill the functional role of an apex predator?

“…Fort Hood is surrounded primarily by agricultural land with larger urban areas to the south. For landscape, climate, and vegetation descriptions, see Avrin et al (2021). The land is primarily used for military training, including live weapons, aviation, and mechanized maneuvers, but recreation activities, such as hiking, hunting, and fishing, are also allowed as well as some cattle grazing (Hayden et al, 2000).…”

“…Grid order was different each year. For specifics on camera trap setup, see Avrin et al (2021). In 2018-2019 and 2019-2020, we deployed scent lures of sardines or fatty acid tablets at 93 camera traps (two-thirds of the cameras) as part of a study on the efficacy of scent lures (Avrin et al, 2021).…”