Monitoring and detection of feral cats on Auckland Island

Abstract

In order to conserve important biodiversity values, eradication of feral cats (Felis catus) is planned on Auckland Island in the New Zealand subantarctic region. This eradication will require detailed knowledge of the abundance, distribution, movement behaviour and detection probability of cats on the island. We investigated these parameters on a peninsula at the northern end of the island using live trapping, camera trapping, and scat searches with and without detection dogs. Here, we compare the results of these methods, and discuss their utility for the planned eradication. Four cats were captured and fitted with GPS collars. Camera traps with 500 m spacing detected all these individuals on multiple occasions, and at multiple locations. At least 12 other individuals were also captured on camera. Excluding every second camera (to simulate 1000 m spacing) resulted in failure to detect 32% of known individuals. Population density estimates from camera trapping varied from 0.7-1.0 cats km -2 . Humans found 29 cat scats, and dogs found 33. Genetic analysis estimated that these came from a minimum of ten individuals. Camera trapping should be repeated during the operational and confirmation phases of the eradication to monitor spatial and temporal variation in cat density, detect survivors, and help confirm eradication success. Scat collection, with and without dogs, can supplement data from camera trapping. With larger sample sizes of scats, DNA profiling may also allow cat abundance to be estimated.

Feral cats on Rakiura Stewart Island: population attributes and potential eradication tools

“…We used the 'Evaluate SECR log likelihood' function in DENSITY 5.0 to evaluate whether this buffer was appropriate (Efford 2012). For further explanation see Glen et al (2022).…”

The next frontier: assessing the feasibility of eradicating mammalian pests from Auckland Island

“…An island-wide grid of trail cameras will be installed before the preceding mouse eradication to take a baseline measure of the cat population and will be the primary tool used to detect cats and monitor changes in the cat population throughout the eradication (Glen et al 2022b). The camera grid will run for the duration of the eradication and will be regularly serviced to facilitate rapid response to cat detections.…”

“…A targeted response to detections will be used as the scale of the island inhibits blanket use of grid trapping. Moreover, our trials enhanced the efficiency of elimination tools by targeting where we detected cats on the camera network and training cats to a food type or site before setting traps (Glen et al 2022b). DNA profiling of fresh scat samples in the final stages of eradication will help to verify detection results and provide confidence of success to managers.…”

“…To eradicate cats, software for automated processing of trail camera data is needed to manage a camera network across the size of Auckland Island. This development relies on improving image processing capability to reliably filter falsely triggered images (without an animal in frame) and preferably identify when a cat is present (Glen et al 2022b).…”

“…A toxic bait to target cats (cat bait) would improve the likelihood of success and opportunity for rapid completion (within 12 to 18 months) by efficiently exposing all surviving cats over the whole island, including on terrain inaccessible to trappers (Parkes et al 2014;Fisher et al 2015;Cox et al 2022b;Glen et al 2022a). Trappers could then more quickly move to mopping up surviving cats with the aid of the islandwide network of trail cameras to target effort (Glen et al 2022b). There would then be less risk of cats becoming wary and avoiding detection than when relying on trapping alone.…”