Poisoning Incidents in the Field

When ARs have been used to control rodents and vertebrate predators in conserved areas, there have been instances of both primary and secondary poisoning. In New Zealand, such incidents have been observed on islands where bait treated with brodifacoum has been used. Casualties have included native raptors, such as the Australasian harrier (Circus approximans) and morepork (Ninox novaeseelaniae), as well as other species, such as the pukeko. Western weka (Galliralus australis), and 

As discussed earlier, a problem with these field incidents is that the low levels of rodenticides found in many of the poisoned birds are of similar magnitude to those in birds surviving exposure. A low residue level may signify everything or nothing. Additional evidence is needed to establish that the concentrations of rodenticide present in the livers of birds or mammals found in the field are sufficient to have caused death, for example, the presence of hemorrhaging in the carcasses. 

In summary, there is as yet no clear evidence that superwarfarins have caused any widespread declines of predators and scavengers that feed on rodents. However, the persistence and very high cumulative toxicity of these compounds suggest that they could pose a serious hazard to such species if they were to be more widely used. The situation needs to be kept under close review. 

Organic Pollutants An Ecotoxicological Perspective, Second Edition 

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