Anticoagulant rodenticides, in particular second-generation products (active ingredient: bromadiolone, difethialone or brodifacoum), are very toxic with the intent that a single feed on the compound is enough to kill a rat. These poisons are also very persistent, which means that a dead poisoned rodent can be deadly if scavenged by other wildlife. Further, bait aversion can be a challenge when trying to trap rats, hence rodenticides are designed to be slow reacting compounds to reduce the likelihood of rats associating getting sick and dying from eating the bait. Therefore, it can take up to 7-10 days before a rat dies from eating rodenticides. During this lag-time the exposed rat can go back to the bait station and eat more poison, ingesting more than what is required for a lethal dose. Exposed rats slowly get sick and sluggish from eating the bait which makes them susceptible to being predated upon by an owl or a pet.

All types of rodent poison can sicken and kill wildlife and pets, either directly or indirectly. When non-target insects or animals feed on the bait they can transfer the poison up the food chain, where it will have a cumulative impact on larger predators.

Check out this graphic from Raptors are the Solution to see just a few of the pathways poison can travel in this toxic food web.

Annually raptors that get admitted to the Orphan Wildlife Rehabilitation Society (OWL), show signs of being rodenticide poisoned, and some poisonings are fatal. A subset of the deceased individuals get tested for rodenticides and of those about ~74% have residues of at least one rodenticide. This does not mean all the exposed raptors died from rodenticide poisoning. Many of the raptors tested were victims of road mortality, but we cannot rule out that there might be indirect effects from ingesting poison, such as making the raptor feeling unwell and being less responsive and more at risk of getting hit by cars, flying into windows or susceptible to starvation.