Identification of individual wild possums from bite marks

Abstract

New Zealand’s brushtail possum (Trichosurus vulpecula) abundance is monitored by the trap-catch method where the proportion of traps catching possums is used to index its abundance. The comparatively new waxtag® method where the proportion of interfered tags is similarly used as an abundance index has advantageous properties, including its minimal risk to non-target fauna, low operational cost, and ease of use. However, unlike the trap-catch method, the bait can be interfered with by many individual animals of multiple species, and likewise a single individual can interfere with multiple baits, which is an intrinsic drawback to the method, confounding the results due to an unknown probability of multiple interference of bait. We addressed the issues by identifying the responsible species and individual animals from the bite marks left on the waxtags. Possum and rodent bite marks were defined by measuring single tooth-mark widths. A novel method to identify individual animals was developed by applying the forensic toolmark examination principle to microscopic features observed on the bitemarks. This demonstrated that bitemarks can be used to reliably identify individual animals.