Animal pests: tracking tunnel indices of small mammal abundance version 1.0

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This is an overview of the best practice guide for DOC staff to follow when using tracking tunnels to measure rodent and/or mustelid relative abundance (see ‘DOC tracking tunnel guide v2.5.2’— docdm-1199768).

The technique uses a ‘run through’ tunnel containing two pieces of paper or card either side of a pad coated or soaked with ink. As an animal passes through the tunnel it picks up the ink on its feet, then as it departs from the tunnel it leaves a set of footprints on the papers or cards.

Tracking tunnels are set on randomly orientated lines, and results are recorded as the average percentage of tunnels containing rodent or mustelid tracks per line. The number of tunnel lines that are needed depends on the size of the study site and whether rodents or mustelids are being surveyed. Six to twenty tunnel lines are usually required, but consult table 1 in ‘DOC tracking tunnel guide v2.5.2’ (docdm-1199768) for more details. This technique only provides a coarse index of relative abundance of rodents or mustelids; it is not a direct measure of population density as the index can be influenced by variation in activity. The technique is best suited for providing simultaneous comparisons of the relative abundance of rodents (particularly rats) or mustelids between similar habitat areas (e.g. treatment and non-treatment), or gross changes in relative abundance over time at a single site. Hedgehogs are often detected in tracking tunnels (Jones & Sanders 2005) but it is unknown how sensitive the technique is to the presence of these animals. Initial set-up costs can be high, but the ongoing costs are somewhat less because the tracking tunnels remain permanently in place between monitoring sessions.