Visual and taste cues for minimising native bird interactions with toxic 1080 baits – a review of current practices

Non-target risk from the use of vertebrate toxins for pest control is an ongoing issue globally. In New Zealand, toxic bait for aerial control of possums and rodents is dyed green and contains cinnamon oil, both of which are thought to reduce the risk that birds will eat the bait. It has been suggested for some time that blue dye may be a more effective feeding deterrent than green dye. While both green and blue dye reduce the risk that birds will feed on bait, the available evidence is not sufficiently strong to suggest a significant improvement in repelling birds by switching from green to blue. Cinnamon oil, at the nominal concentration in bait, may have some bird repellent effects, but these are likely to depend on its origin (bark or leaves) and the freshness of the bait (as it evaporates relatively quickly from bait after manufacture). Bait colour, including ultraviolet, is also an important cue in avoidance learning by birds and should be considered in more detail in future studies of specific bird repellent additives to bait for possum and rodent control. Further research is needed to optimise the use of visual cues in bait, both for their inherent repellency (e.g. green vs blue; optimal concentration of dye) and for their effectiveness in promoting avoidance learning. It would also be worth investigating an alternative compound to cinnamon as a mask for 1080; ideally such an alternative would have enhanced stability and bird repellent properties.