Monitoring for the presence of invasive arboreal rodents: an assessment of monitoring tools across forest strata

Abstract

Accurate detection of invasive rodents is essential to guide appropriate management responses, including effective control. Due to the arboreal behaviour of some invasive rodent species, above-ground monitoring may provide managers with a clearer picture of rodent presence. Numerous ground-based rodent monitoring tools have been tested and compared, but how these tools perform in an arboreal context is unknown. Our study sought to compare the strata-specific detection capability of three widely applied rodent monitoring tools using a nested design. Over two month-long periods, we deployed 180 monitoring stations at the ground, mid-storey and canopy across 30 forested sites. Each monitoring station consisted of a camera trap, chew card and tracking tunnel positioned to detect rodent presence. Device agreement was high, with all devices detecting rodent presence at 50% of stations. Chew cards were the most sensitive above-ground tool, implied by positive rodent detection 90% of the time, while tracking tunnels and camera traps generated a positive detection 74% and 75% of the time respectively. Low equipment costs also made chew cards the most cost-effective method. Detection performance differed according to the strata in which the device was deployed, thus a combination of methods that includes camera traps and chew cards was most effective when implementing a three-dimensional rodent monitoring network in forested settings. While not all methods are equal, traditionally ground-based rodent monitoring devices can be used to effectively monitor arboreal rodent activity. We provide evidence-based guidance for invasive rodent monitoring in an arboreal context to support future invasive rodent population control or eradication programs.