Stability of bird repellents used to protect kea (Nestor notabilis) during aerial 1080 cereal operations

Aerial poisoning with cereal bait containing 1080 toxin is known to pose a risk to the kea (Nestor notabilis), an endemic New Zealand mountain parrot. For a bird repellent to protect kea during such poisoning operations, it must be effective in bait for 4–12 weeks after the bait is manufactured, as this is when most aerial 1080 cereal operations take place. Two bird repellents have been shown to be effective with captive kea, d-pulegone and 9,10-anthraquinone. The stability of d-pulegone required further investigation because previous monitoring showed d-pulegone declined to very low levels in cereal baits 30 weeks after manufacture. Repellents were incorporated as ingredients during the normal bait manufacturing process. The estimated initial concentrations of d-pulegone in five batches of non-toxic prefeed bait and four batches of toxic bait at manufacture were only 52–88% of the nominal concentration. The superheated steam that was used to condition bait ingredients probably contributed to d-pulegone loss during manufacture. Thereafter, the estimated rate of decay of d-pulegone in storage ranged from 3.2% to 6.6% per week, so none of the batches of bait met the operational target concentration of 0.12–0.22% wt/wt at 4–12 weeks after manufacture. By contrast, the concentration of anthraquinone on receipt in one batch of repellent toxic baits was very close to the nominal concentration and did not decline over a 6-month period. Future research on d-pulegone should investigate stabilisation, following which the effectiveness of d-pulegone as a bird repellent should be retested, either alone at a higher concentration or in combination with a ‘secondary’ repellent. Future research on anthraquinone in cereal pellets should focus on possum control, as indications are that rat kills are adversely affected by its use in cereal baits.