REVIEW OF THE TOXICITY AND IMPACTS OF BRODIFACOUM ON NONTARGET WILDLIFE IN NEW-ZEALAND

Brodifacoum, an anticoagulant used in cereal-based baits for the contr ol of vertebrate pests, especially rodents, may be accidentally ingest ed by non-target species. In birds, its acute toxicity varies from an LD(50) of <1 mg/kg in pukeko to >20 mg/kg in paradise shelduck. Fourte en indigenous and eight introduced bird species have been reported kil led by field use of brodifacoum in New Zealand. Populations of three s pecies (western weka, Stewart Island weka, and pukeko) have been sever ely reduced in poisoned areas. There are no published data on the acut e toxicity of brodifacoum in bats, reptiles, or amphibians. Invertebra tes are unlikely to be killed by anticoagulants. Because of the high t oxicity of brodifacoum, all vertebrates that eat baits or poisoned pre y are at risk. Brodifacoum is only slowly eliminated from the liver, a nd therefore accumulates in vertebrates if there are repeated exposure s to the toxin, which increases the risk of death. In New Zealand, ind igenous non-target species most at risk from eating brodifacoum in cer eal-based baits are herbivorous and omnivorous birds (e.g., weka, puke ko, and saddleback). The species most at risk from secondary poisoning are predatory and scavenging birds such as weka, Australasian harrier , southern black-backed gull, and morepork. Insectivorous birds, bats, lizards, and frogs are probably least at risk. However, laboratory an d field trials are essential to determine the actual risks, and reduce scientific uncertainties. The risks of pest control must be carefully balanced against the benefits. These benefits can be substantial wher e introduced mammals threaten native species with extinction.