Secondary Poisoning occurs when a predator or scavenger eats a poisoned animal and becomes poisoned itself. This frequently occurs with predators like eagles, badgers, owls or house cats consume a rodent that has eaten rat poison but has not yet died. Scavenging animals, (including pet dogs), may also eat rodents that have died from poisoning.
Secondary poisoning is cruel. The affected predator often dies slowly and painfully as the small amount of poison consumed is not enough to kill it quickly but is still enough to reduce its hunting ability or cause problems with internal organ function.
What's the big deal?
Secondary poisoning can kill the predators of rodents and other small mammals, which may make your pest problem worse.
Continuous use of rodenticides can eventually result in rats and mice developing a high tolerance, leading to stronger and stronger poisons or larger doses being necessary.
The resulting death of non-target animals is often slow and painful.
Wildlife is already threatened by habitat loss, degradation, and fragmentation. This is an extra threat that some populations can't manage.
A study out of California found that 85% of bobcats and cougars have rat poison in their systems*
Stronger is not better: the different types of poison
First generation rodenticides are a bit less strong and require a few doses over a few days to kill the rodent, but once the proper amount is eaten, the poison acts quickly. This means the sick or dead rodent is less likely to harm a predator because the potency is lower and increases the chance the predator may survive the dose.
Second generation rodenticides are technically lethal after one dose, but they act very, very slowly so the rodent keeps moving around for days, eating more and more bait. This results in the rodent eating excessive doses of poison before dying, so if it does end up eaten by a hawk, owl, or pet cat, there will be enough poison in its body to kill that animal too.
Rodenticides don't just smell delicious to mice and rats. They will attract many other animals, even pet cats and dogs.
In addition, rodents are not the only type of animal that is affected by rodenticides, either. All birds, reptiles, and mammals (even humans!) that ingest the poison bait will become ill, with the level of sickness depending on the type of poison used as well as the amount eaten.
If you must use rodenticides, be sure not to put the bait where pets or other wildlife can find it. Always read the instructions carefully for any warnings before using it, and never put it out "just in case" of rodents.
Excessive use of herbicides and insecticides are continuing to reduce communities of wildflowers, important pollinators, and other helpful insects every year.
Pollination is vital for the growth of our fruits and vegetables, but using insecticides often kills native pollinators directly, which then increases the need to bring in artificial hives of non-native honeybees. Many herbicides also affect the digestive systems of bees and make them sick or even kill them.
Hundreds of songbird species also rely on these insects and flower seeds for food, so excessive chemical use can put their survival in jeopardy.
Predators as natural pest control
If you keep some habitat for predators on your property they can help you to keep rodent populations low. Birds of prey like hawks and owls like high perches to hunt from. You can encourage these birds by providing T-posts and nest boxes.
Snakes are also great at controlling rodents and can even follow them down their tunnels to take out whole families. Check out our snake resources for information on identifying snakes and creating snake habitat.
Some small and medium sized mammals are also voracious rodent predators. Badgers, bobcats, weasels and coyotes all depend on rodents to survive.