Unwelcome visits from rats or mice can make us want to reach straight for the rodent bait. While we ensure baits are put out of reach of children, pets and other animals, we rarely think about where rodents go after they have eaten baits. In fact, we probably try and think about it as little as possible.
The most commonly used rodent poisons are anticoagulant rodenticides (ARs). These act as blood thinners, so rats and mice can consume a lethal dose but not feel sick until later.
Newer ARs, called second generation anticoagulant rodenticides (SGARs), are powerful enough that a single feed can be lethal. But, because of the time lag between taking a bait and feeling the effects, poisoned rodents can wander around like walking time bombs. Predators that naturally eat rodents, like owls and kestrels (right), can then easily consume multiple poisoned rodents, in turn becoming poisoned themselves.
SGARs don’t break down quickly – some can stay in tissues and organs for months, even years. Unfortunately this just makes it easier for these bigger animals to get a lethal dose of toxins.
What are the differences between First and Second Generation products?
The key differences between earlier, first generation anticoagulant rodenticides (FGARs) and SGARs is how long the toxins remain in the body. FGARs break down quicker, and so there is less chance of larger animals being poisoned. SGARs can stay in body tissues for months or even years. Yet Australia has little regulation on their use - SGARs can be easily purchased in hardware and grocery stores across the country.
The link between SGARs and Australian birds was found when researching declining Southern Boobook populations. Almost 73% of samples tested from boobooks in southwest WA had detectable exposure to ARs. Of even greater concern, about 18% of all the boobooks tested had levels of exposure that were high enough to kill them directly. Almost all the toxins were identified as SGARs. These were found in both urban and rural birds.
While other factors may also be impacting the decline of these small predators, the potential impact of anticoagulant rodenticides cannot be ignored.
The use of FGARs and SGARs is sometimes necessary in conservation efforts, particularly in protecting seabird colonies on islands.
The USA Environmental Protection Authority, Health Canada and the EU have all, in recent years, placed tighter regulations on anticoagulant rodenticides including limiting the usage of SGARs to licenced professional pest controllers only and supplying FGARs to the public in pre-prepared and tamper proof bait stations.
