Forest invertebrates found on baits used in pest mammal control and the impact of sodium monofluoroacetate ("1080") on their numbers at Ohakune, North Island, New Zealand

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Abstract
We listed all invertebrate taxa found in contact with non‐toxic carrot and pollard baits commonly used for poisoning pest mammals with sodium monofluoroacetate ("1080") over two winters (1995 and 1996) at 12 sites in mixed podocarp and hardwood forest near Ohakune, central North Island, New Zealand. Invertebrates were found on 12% and 23% respectively of the 11 000 carrot and 6000 pollard baits observed. The usage of baits varied with time, peaking in October, and for pollard baits usage also varied between sites. Of the 113 taxa identified, ten taxa contributed ≥1% each of the total number of invertebrates, and three made up 66% of the total. The numbers of three of the four species most commonly found on baits did not correlate with the numbers of those species caught in nearby pitfall traps. The results suggest that at any time only a small proportion of baits have invertebrates on them, and the few individuals per bait represent a small section of the fauna present in the litter. Observations of the impact of 1080 on invertebrates were made at the same Ohakune site over two winters (1996 and 1997). Invertebrates were found on 43% of over 22 000 toxic and non‐toxic pollard baits examined. A total of 133 taxa was identified, of which only 13 taxa each comprised ≥ 1% each, and three taxa together accounted for 67% of the total number of invertebrates visiting baits. The proportion of baits with invertebrates on them, and the number of invertebrates per available bait, were both significantly lower when 1080 was present in a bait. Recovery of invertebrate numbers started within six days of toxic bait removal, but subsequent application of toxic baits further reduced the number of invertebrates observed. We did not determine whether the reductions in invertebrate numbers were due to poisoning or aversion to 1080. There was no reduction in invertebrate numbers on non‐toxic baits placed at 20 cm or more from a toxic bait. These results are relevant to assessments of the risk to non‐target species from primary and secondary poisoning while controlling pest mammals by aerially broadcasting baits laced with 1080.