Predator Odors as Repellents to Brushtail Possums and Rabbits

Repellents are being developed as an alternative to the use of poisons, traps, or firearms for controlling damage to forest and farm plantings by the introduced Australian brushtail possum (Trichosurus vulpecula) and European rabbit (Oryctolagus cuniculus). Such repellents need to protect seedlings from irreversible damage for at least 6 months after application. Seven synthetic predator odor compounds were compared with "Treepel, " a moderately effective commercial repellent, by assessing relative browse on treated Pinus radiata seedlings in pen tests. Predator odors were repellent to both animals. Generally they were more repellent to possums than to rabbits, but the predator odor-based TOM (formulation confidential) was particularly repellent to rabbits. In a longer field trial at a site heavily infested with rabbits, both TOM and Treepel gave good initial protection, TOM being more effective. However, effectiveness declined after 56 days, and extensive browning was affecting foliage, particularly after treatment with TOM. The formulation of TOM therefore needs refinement to prevent phytotoxicity and to prolong effectiveness. The results support the existence of a sensory mechanism that enables herbivores to avoid predators by detecting by-products of meat-eating animals. If this mechanism is innate for all herbivores rather than interspecific for particular herbivores and predators, development of broad-spectrum herbivore repellents may be possible.