Repellents with potential to protect kea and other native birds from aerial poisoning for possum and rat control

Concern about non-target risks to native birds, particularly kea (Nestor notabilis), from aerial poisoning has prompted the evaluation of potential repellent compounds that could be incorporated into the cereal pellet bait used for possum (Trichosurus vulpecula) and rat (Rattus spp.) control. Initial trials of d-pulegone and anthraquinone were not wholly successful, with the former having poor stability in bait and the latter reducing bait uptake by rats. While research to stabilise d-pulegone in bait remains an option, a review of alternative compounds was undertaken to assist with decision-making about future directions for research, including consideration of possible formulation issues and cost. Most of the information reviewed related to use of repellents for crop protection where the aim is to reduce economic loss rather than prevent feeding on the crop, whereas preventing feeding is the primary aim for native bird protection. A further constraint was the lack of information for many compounds on response of rodents and possums. Cinnamamide, tannic acid, caffeine, garlic oil, ortho-aminoacetophenone, and thiram were identified as possible candidates and evaluated in relation to their potential to repel native birds from eating cereal baits without affecting efficacy for possum and rats. Cinnamamide, caffeine, and thiram, while effective as bird repellents, are likely to be repellent to rats at concentrations suitable for use with native birds, including kea. The little information found suggested that garlic oil was repellent to birds; it has not been formally tested on possums and rats, but anecdotal evidence did not suggest strong aversion. Ortho-aminoacetophenone appears effective as a bird repellent, but its repellency for possums and rats requires clarification. Tannic acid has some efficacy as a bird repellent, and is not repellent to possums and rats at lower concentrations. It is not clear if tannic acid exerts its effect solely as a primary repellent or whether it also has secondary repellent effects. In order from most to least promising, tannic acid, ortho-aminoacetophenone, and garlic oil are worthy of further investigation. Because each compound has demonstrated some efficacy as a bird repellent, initial testing should focus on screening against possums and rats.