Applying the precautionary principle to the issue of impacts by pet cats on urban wildlife

Despite evidence that pet cats prey on urban wildlife and may transmit disease, there is uncertainty over whether they cause declines in wildlife populations. The uncertainty fosters disagreement about whether and how pet cats should be managed, and hampers the implementation of regulations. We suggest that the precautionary principle could be used in this context. The principle mandates action to protect the environment when there is a scientifically plausible but unproven risk, and provides a rationale for immediate intervention to protect wildlife from pet cats while we await definitive studies. In applying a 4-step guide for implementing the precautionary principle, we argue that: (i) current data documenting wildlife mortality caused by pet cats satisfy the precautionary trigger of scientifically plausible risk; (ii) the risk of significant declines or local extinctions of threatened wildlife, coupled with uncertainty in establishing population declines in response to pet cats, argue for strong levels of precaution; (iii) precautionary measures that should be considered include, but are not limited to, restrictions on the maximum number of cats allowed/household, mandatory sterilisation and registration of pet cats, curfews, requiring pet cats roaming outdoors to wear collar-mounted predation-deterrents or compulsory confinement of cats to their owners' premises; and (iv) the principle's requirement for extensive consultation in implementing precautionary measures should encourage collaborations involving conservation biologists, veterinarians, animal welfare activists, concerned citizens and municipal officers. Adherence to these steps should assist in choosing actions that have broad support and are applicable to unique local circumstances