Efficacy of bird repellents at deterring North Island robins (Petroica australis longipes) and tomtits (P. macrocephala toitoi) from baits

North Island robins (Petroica australis longipes) and tomtits (P. macrocephala toitoi) are at risk of being poisoned during pest control operations in New Zealand. Robins are deterred from feeding on diets containing primary repellents (e.g. blue colour, d-pulegone) and secondary repellents (e.g. illness-inducing materials such as anthraquinone, which induce taste aversions). We tested, with wild robins, primary and secondary repellents surface-coated onto dough baits, over 4 days on Tiritiri Matangi Island. In comparison with green-coloured cinnamon-scented control baits, robins averaged at least 71% fewer pecks at blue-coloured, anthraquinone (0.09% wt/wt) baits with or without cinnamon oil (commonly used as a bird repellent) and 0.045% wt/wt anthraquinone baits with cinnamon oil or d-pulegone. There were no significant differences in pecking rates among the repellent formulations. Pecking rates at baits containing 0.09% anthraquinone were almost nil by Day 4.
The efficacy of 0.09% anthraquinone at protecting tomtits from poisoning was tested in a commercial aerial possum control operation at Whareorino Forest using carrot baits. Prefeed (2 kg ha^–1) and toxic baits (3 kg ha^–1; 1080 at 0.12% wt/wt) were coated with anthraquinone (at 0.57 and 0.45 mg per kilogram of carrot, respectively), blue dye and an orange-flavoured lure and laid over an area of 1400 ha. Tomtit abundance, measured using sightings of territorial males along transects before and after the control operation, increased significantly more in the bird-repellent-treated block than in an adjacent block receiving the standard prefeed and green dye plus orange-lured toxic carrot baits. Possum catch rates declined further in the ‘Repellent’ block than in the ‘No Repellent’ block, but the field trial requires replication in a more effective possum poisoning operation. These trials have demonstrated the efficacy of repeatedly presented bird repellent formulations combining an illness-inducing agent, an unattractive colour and a distinctive flavour for protecting ground-feeding New Zealand forest birds from poisoning during mammalian pest control.