Context. Sodium fluoroacetate (1080) is a vertebrate pesticide used in several countries, including New Zealand, where it is the main pesticide for controlling brushtail possums (Trichosurus vulpecula) – a significant agricultural and conservation pest. There is growing concern internationally about the impacts of vertebrate pesticides, including 1080, on pest animal welfare.

Aims. Behavioural changes and time to loss of consciousness of possums after 1080 ingestion in carrot baits were determined to compare the animal welfare impacts with other possum pesticides.

Methods. Eight lethally dosed possums and eight that consumed a dose intended to be sublethal were observed until death or recovery but not handled. Another nine lethally dosed possums were handled to determine responses to stimuli, indicating time to loss of consciousness.

Key results. Unhandled, lethally dosed possums died after 11 h 26 min ± 1 h 55 min (mean ± s.e.m.). Half had abnormal appearances and postures 1 h 50 min ± 9 min after consuming baits. Seven showed retching, and three vomited, over 27 ± 12 min from 2 h 53 min ± 13 min. Lack of coordination began 3 h 37 min ± 32 min after dosing, then possums spent most of the time until death lying, showing spasms and tremors. Five showed seizures while lying prostrate. Possums receiving a nominally sublethal dose all showed signs of poisoning, including abnormal postures, lethargy, lack coordination, retching, spasms or tremors, and a cessation of grooming, feeding and activity. One died 18 h 15 min after dosing, experiencing two seizures within 30 min of death. Response to handling, indicating total loss of consciousness, was lost in two possums before death.

Conclusions. Possums ingesting a lethal dose of 1080 experienced ~9.5 h of changed behaviour and lost consciousness close to death, although awareness was likely reduced sometime beforehand. Possums ingesting a nominally sublethal dose experienced some effects of poisoning.

Implications. These impacts are intermediate compared with other possum pesticides in New Zealand. Nevertheless, the potential for consciousness during and after retching and seizures is undesirable for animal welfare. Further work is encouraged on alternatives to 1080 and means of reducing its impact on animal welfare.