The Pelican-- Rodenticides Poisoning Raptors

By Eiji de Queiroz 

In our community, there is a large problem of raptors being killed by rat poisons. Once, I was walking around in Verdi when I found a dead Great Horned Owl laying on the ground. It didn’t look like it was very old, and there weren’t any visible injuries that could’ve caused its death. I realised that this owl had probably been killed by ingesting rat poison from eating rodents. 

This is a picture of a different owl, taken in Idlewild Park.

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​Many people use rodenticides in order to stop rats from eating their food, without knowing about the many negative impacts rodenticides have on local wildlife other than rats. Most rat poisons used today fall under the category of SGARs, or Second-Generation Anticoagulant Rodenticides. These poisons work by stopping blood clotting in whatever creature ingests them, causing small cuts to become very dangerous, since there’s no blood clotting to stop the flow of blood. Because of this, the rats end up dying of blood loss, often from internal bleeding that would normally be unnoticeable because of blood clotting. Since SGARs rely on small injuries that rats get naturally to kill them, it often takes days, or even weeks, before the rat dies.  This means that, for those few days, there is a rat running around with one or more doses of anticoagulants in its liver.

If a raptor or another predator of rodents eats a poisoned rat, the poison will eventually make its way into the liver of the predator. These poisons can stay inside the liver of one of these predators for months before entirely going away. Because most predators of rats are many times larger than the rats themselves, a single dose of anticoagulants isn’t enough to kill them, and can sometimes have no negative side effects. However, most predators will end up ingesting more than one poisoned rat, which is when it becomes a problem. Even if they don’t die, predators will often experience other negative side effects, such as disorientation and sluggishness. 

A study by the Wildlife Unit of the New York State Department of Environmental Conservation found that nearly 85 percent of dead raptors had some kind of anticoagulant in their liver. At Tufts University, a study found that 100 percent of dead Red-tailed Hawks had ingested rodenticides. 

There have been attempts to stop the impact of rodenticides on wildlife. The use of pellet rodenticides is very restricted in the U.S., and only certain sellers can distribute rodenticides. In California, use of rodenticides is banned completely except for special cases, such as disease outbreaks or agriculture. However, it is still possible to go on Amazon and buy a large bucket of SGARs rodenticides.  

There are many ways to get rid of rats other than rodenticides. There are some rat poisons that aren’t as harmful to predators as SGARs, but most of these are less effective on rats and can still negatively impact predators. Snap traps can kill rats with no risk of harming predators, though again they are less effective than SGARs. Another positive side of snap traps is that they are a more humane way of killing rats, since they basically instantly kill them, causing no pain. Rat proof trash bins can help with problems with rats without actually harming them, and so can other ways of storing food more securely. 

Raptors are important parts of the ecosystem for many different reasons. For one, they eat the rats which the rat poisons are trying to kill. Though they may not be as effective as rodenticides, raptors are the most environmentally friendly rodent killers.