On Camera-Trapping Terrestrial Squamates

摘要

In all fields of wildlife research and management, fundamental biodiversity and species distributional data are required. Yet, the difficulty that wildlife researchers face detecting small and cryptic species, in particular snakes and lizards (squamates), has led to gaps in fundamental knowledge. The lack of fundamental ecological data limits our understanding about the role many squamates perform in ecosystems and diminishes our ability to manage potential threats. Indeed, the dearth of squamate data is so pervasive that the global threat to squamates in 2015 could not be assessed. This situation is of great concern since squamates are a particularly speciose vertebrate group. Collecting fundamental data on squamates is ordinarily achieved with capture, trapping, or visual encounter methods. These methods are often costly, since researchers need to remain in the field for protracted periods, and are ethically questionable due to direct and indirect impacts on target and non-target fauna. Thus, developing survey methods that can effectively, efficiently, and ethically provide fundamental data are paramount for squamate research and management.The most direct solution to ameliorate data deficiency is to improve detection methods and the most direct solution to improve detection methods is to adopt new technologies. In recent decades camera-traps have become a valuable tool for monitoring mammals, fish, and to a lesser extent birds. For example, camera-traps are both more effective and more cost-effective than labour-intensive methods, such as live-trapping, for detecting numerous mammal species. However, the use of camera-traps to monitor squamates hitherto has been limited. While camera-traps have real limitations, their use for detecting squamates has been limited due to misconceptions about camera-trapping technology. It might be that camera-traps are as useful for monitoring squamates as they have been for other taxa, but considerable research might be required to develop an effective method. Hence, this thesis addresses the following question: Is camera-trapping a cost-effective and ethical method for monitoring terrestrial squamates?As camera-traps had not been used to monitor a squamate assemblage, a suitable method needed to be developed. The method would need to detect the range of squamate species occurring in an area, including small species (snout-vent length ≤ 50 mm), and generate ecologically meaningful data. By reviewing how camera-traps function at a technical level, and assessing attempts to use camera-traps for detecting ectothermic species, the Camera Overhead Augmented Temperature (COAT) method was developed. The COAT method positions the camera-trap so as to take overhead images of squamates as they pass under the camera-trap. In the first field trial, the COAT method detected the majority of squamate and mammal species known to occur on the study area. Detections included small squamates with a SVL ≤ 50 mm. Most species could be identified to species-level, and several species could be identified to individual-level. While the results were encouraging, the pilot study did not address the main question of the thesis.With development of the COAT method, the next logical step was to compare the COAT method to existing standard squamate-survey methods to assess whether camera-traps were effective. As a first comparison, the COAT method was compared to cage and Elliott traps and artificial refuges. These labour-intensive methods had been used on the study area since 2011 as part of a long-term monitoring program. The COAT method was found to be more effective and more cost-effective than the labour-intensive methods for detecting squamates and mammals simultaneously, and mammals alone. The COAT method was no more, but importantly, no less effective than the labour-intensive methods for detecting squamates alone. There was weak evidence that the COAT method was more cost-effective than the labour-intensive methods for squamates alone. Importantly, given that several mammal and squamate individuals perished in the labour-intensive methods survey, the COAT method was ethically superior.Despite the encouraging results, six aspects of Version 1 of the COAT method were identified as areas requiring improvement or further analysis. Three aspects related to the instrument (i.e., camera-trap) and three related to the concentration methods. To improve the COAT method the time-lapse trigger, a more sensitive passive infrared (PIR) trigger, and adjusted camera focal length were examined. Both the time-lapse trigger and more sensitive PIR trigger increased squamate detections. Unfortunately, regardless of sensitivity the PIR sensor resulted in biased detections, which the time-lapse trigger did not. It was also revealed that by adjusting the camera’s focal length all squamates, including small species, could be identified to species-level. Thus, the second version of the COAT method dictated that both time-lapse and PIR triggers be used simultaneously, and camera focal length be adjusted.When first designed, two concentration methods were included in the COAT method. Bait, specifically peanut butter and oats, was included to attract mammals, and drift fences were included to channel fauna to the detection zone. Additionally, a cork floor tile was positioned in the detection zone of the camera-trap. It was included to create a thermal contrast between fauna and the background substrate, necessary for the camera-trap to trigger. However, the tile appeared to function as a concentration method. While inclusion of each component was logical, their effects on squamate detections were not empirically tested. Thus, three further field experiments were conducted. The presence of bait and drift fences did not affect squamate detections. Both the presence and material of the tile affected squamate detections. Whether the tile functioned as a concentration method was not clear and could not be explored within the scope of this thesis. Although these experiments did not directly improve the COAT method, they deepened the understanding of how the COAT method functions, and highlighted future research directions.Given the improvements made to the COAT method, a final comparison was required to provide a definitive answer to the main question of the thesis. The COAT method was compared to artificial refuges and pitfall traps. Version 2 of the COAT method was both more effective and more cost-effective than the labour-intensive methods examined for inventorying the squamate assemblage. More squamate species on average were detected per transect with camera-traps than with artificial refuges or pitfall traps. Over the entire survey, all 10 squamate species were detected with camera-traps, yet only seven and six squamate species were detected with artificial refuges and pitfall traps respectively. Again, camera-traps had less impact upon fauna as several squamates and amphibians perished in pitfall traps. With this final comparison, the central question of the thesis could be confidently answered in the affirmative.Development of the COAT method has several important implications. First, this is the first camera-trapping method that can be used to monitor a squamate assemblage. This provides wildlife researchers with a new tool to address both existing and new types of questions. Camera-traps have been used to great effect in mammology, and the COAT method should provide herpetologists those same benefits. Second, by being more cost-effective, the COAT method will save precious research funds and should increase data collection overall. Lastly, the COAT method detects both squamates and mammals simultaneously. Wildlife researchers currently using camera-traps to monitor small-mammals can use the COAT method and include squamates as target fauna. Results from this research are encouraging and provide a critical first chapter in how camera-traps can be utilised to monitor squamates.