Abstract
Practical techniques are required to monitor invasive animals, which are often cryptic and occur at low density. Camera traps have potential for this purpose, but may have problems detecting and identifying small species. A further challenge is how to standardise the size of each camera’s field of view so capture rates are comparable between different places and times. We investigated the optimal specifications for a low-cost camera trap for small mammals. The factors tested were 1) trigger speed, 2) passive infrared vs. microwave sensor, 3) white vs. infrared flash, and 4) still photographs vs. video. We also tested a new approach to standardise each camera’s field of view. We compared the success rates of four camera trap designs in detecting and taking recognisable photographs of captive stoats ( Mustela erminea ), feral cats (Felis catus) and hedgehogs ( Erinaceus europaeus ). Trigger speeds of 0.2–2.1 s captured photographs of all three target species unless the animal was running at high speed. The camera with a microwave sensor was prone to false triggers, and often failed to trigger when an animal moved in front of it. A white flash produced photographs that were more readily identified to species than those obtained under infrared light. However, a white flash may be more likely to frighten target animals, potentially affecting detection probabilities. Video footage achieved similar success rates to still cameras but required more processing time and computer memory. Placing two camera traps side by side achieved a higher success rate than using a single camera. Camera traps show considerable promise for monitoring invasive mammal control operations. Further research should address how best to standardise the size of each camera’s field of view, maximise the probability that an animal encountering a camera trap will be detected, and eliminate visible or audible cues emitted by camera traps.
Highlights
There are few or no proven techniques for measuring the efficacy of control operations targeting small to medium-sized invasive animals such as stoats (Mustela erminea), feral cats (Felis catus) and hedgehogs (Erinaceus europaeus) in New Zealand, especially when these animals are in very low abundance
Animals running at high speed were the most common reason for failure to detect stoats during an encounter, long grass may have contributed to some missed detections
The Reconyx passive infrared (PIR) sensor took 1– 2 s longer to detect stoats in such long grass, and on two occasions the resulting photographs could not be identified because the animal was partly obscured
Summary
There are few or no proven techniques for measuring the efficacy of control operations targeting small to medium-sized invasive animals such as stoats (Mustela erminea), feral cats (Felis catus) and hedgehogs (Erinaceus europaeus) in New Zealand, especially when these animals are in very low abundance. Camera traps have demonstrated potential for population assessment, including both relative and absolute density estimates [1,2,3,4,5,6]. A key challenge in using camera traps to estimate relative abundance of animals is how to standardise the size of each camera’s field of view so that results are comparable between different places and times. This problem has recently been addressed by setting camera traps facing the ground from a fixed height [7], which results in higher detection probabilities for some species [8]. By ensuring that each camera samples an area of the same size, the number of detections of a species per camera can be used as an index of relative abundance
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
