Chew-track-cards: a multiple-species small mammal detection device

Detecting the presence of invasive mammalian pests is expensive, particularly where multiple species of interest are sympatric, yet is key to determining when, where and how much control to do, and the effectiveness of that control. Here we describe the efficacy of a simple new and cheap device, the chew-track-card (CTC), both as a potential tool for simultaneously indexing the relative abundance of sympatric small-mammal pests, and for cheaply and comprehensively mapping the distribution of these pests over large, remote areas. The CTC is an interference device that can record both tooth impressions and the footprints of animals interacting with it. Several studies comparing CTC indices (CTCIs) with established indices of possums and rodents are reported. Possum CTCIs were positively and significantly correlated with established trap-catch indices (TCI), WaxTag® and faecal pellet indices of possum abundance. The relationship between possum CTCI and TCI in seven study sites was always positive and, with adequate sampling, statistically significant, but was also variable, probably due to monitoring protocols differing between trials. Rat CTCIs were also positively correlated to tracking tunnel indices, but these two indices were unrelated for mice. Standard leg-hold trapping cost 29－46 times more per possum detection than for CTCs during a large-scale survey of the Hauhungaroa Range. CTCs are a sensitive and cost-effective means of detecting the presence of small mammalian pests, especially possums and rodents. They also potentially provide a robust tool for indexing low density populations of such pests, particularly possums and rats, although further calibration of CTC indices of pest abundance with standard indices is required. Also, the consequences of interaction between abundant pests, particularly rats, on CTC detection rates, and means to reduce these interactions, need further investigation.