Mortality of northern New Zealand dotterels (Charadrius obscurus aquilonius) following an aerial poisoning operation

The anticoagulant brodifacoum is widely used for the control and eradication of vertebrate pests in New Zealand. During poisoning operations with this toxin, some native birds eat baits and die. Because brodifacoum persists in the environment, other birds may suffer secondary poisoning from eating animals that have ingested the poison baits.We describe here high mortality of New Zealand dotterels (Charadrius obscurus) following an aerial brodifacoum operation at Tawharanui Regional Park, North Auckland, in 2004. At least 50% of the dotterels in the area at the time of the operation disappeared or were found dead; one bird found freshly dead had a high liver level of brodifacoum residue. Sandhoppers (Talorchestia spp.) are a common food item of New Zealand dotterels. Sandhoppers at Tawharanui ate baits and accumulated brodifacoum and provided a potential route for transmission of the toxin to dotterels. Three pied stilts (Himantopus himantopus) and one spur-winged plover (Vanellus miles novaehollandiae) were also found dead. These records appear to be the first to document probable secondary poisoning of shorebirds in New Zealand. There was no apparent mortality of variable oystercatchers (Haematopus unicolor). Measures are suggested to reduce shorebird mortality in future operations of this type. Monitoring of New Zealand dotterels and other shorebirds during other types of poisoning operations in coastal areas is also recommended.