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The mohua or yellowhead (Mohoua ochrocephala) is an endangered, hole-nesting forest bird endemic to New Zealand. Mohua suffer periodic population crashes due to severe predation by the introduced stoat (Mustela erminea). In 1990, a stoat population irruption provided an opportunity to reassess the impact of stoat predation on mohua and to test two linked hypotheses: that adaquate control of stoats by trapping is possible, and that it is a viable management option to assist mohua recovery. The primary experiment (summer 1990/91) was repeated in the summers of 1991/92 and 1992/93 when stoat numbers were lower. Mohua productivity and adult female mortality were compared in two study areas, one trapped and one untrapped, in the Eglinton Valley, Fiordland. Sixty-two stoats were caught in the 50 ha trapped area during summer 1990/91. The fledging of many first clutches, and the laying of second clutches, coincided closely with the period when high numbers of stoats were being caught in traps. Eighty percent of the nests in the trapped area fledged young, compared with only 36% in the untrapped area. Pairs produced nearly twice as many young in the trapped area. A higher proportion of breeding females disappeared from the untrapped area. In the two subsequent summers, 29 and 14 stoats were caught, and breeding success was higher than previously recorded in both trapped and untrapped areas. We suggest that trapping in the year following a stoat irruption may also be warranted.

Although Talon® baits containing brodifacoum have been used successfully in eradicating rats from some of New Zealand’s offshore islands, little is known about any environmental effects of this toxin. We sampled invertebrates, blackbirds, soil, and water at intervals of 2 days to 9 months to determine whether brodifacoum residues were present after aerial distribution of Talon® 20P cereal pellets on Red Mercury Island and after bait-station use of Talon® 50WB wax-coated cereal blocks on Coppermine Island. No brodifacoum residues were found in soil, water, or most (99%) invertebrate samples. Low to moderate residues were found in one sample of slugs collected 2 days after aerial sowing. Tissues from all birds (n=4) and rats (n=3) found dead and livers from all six birds collected alive 8 months after aerial baiting also contained low to moderate residues. These preliminary results suggest that few invertebrates are likely to be contaminated as a result of Talon® baiting. Tentatively, we suggest that although some invertebrates may eat Talon® baits, it appears that the brodifacoum is either metabolised and/or excreted within a few days. The dead blackbirds found, therefore, were more likely to have been killed by primary than by secondary poisoning. Further monitoring for brodifacoum residues after Talon® operations should be undertaken to confirm that contamination of invertebrates, soil, and water is unlikely. Some bird species may be at risk from Talon® baiting. Likely effects on population levels of such species should be considered to help assess the risk and benefits of Talon® use in rodent eradication.