Rat poison kills by use of the ingredient warfarin, or a second generation thereof, which thins the blood. In small doses, humans take a similar drug known as cumaden to prevent strokes. In high doses, these kill by causing the organism to bleed internally — massively. It’s a horrible, tortuous death. It should not be allowed. Rats can be eliminated in a more humane manner if need be.
Very small doses of rat poison may not immediately kill the owl, hawk, or coyote that consumes the poisoned rat, but the effects are just as insidious over a longer period of time. The poison accumulates and compromises the ability to live in various ways, most notably by slowing them down. They are not as alert or as fast or as acute as they once were, so living becomes more difficult and even dangerous for them.
One of the effects of rat poisons on coyotes is that it compromises their immune systems, leaving them particularly vulnerable to parasites, including mites of all types. The worst, of course, is mange. Rat poison doesn’t cause mange, of course, but it can be a highly contributive factor because it weakens the immune system which fights off these mites. If you see a coyote whose fur is riddled with mites, or who has mange, it may very well be rat poison which allowed the mite infestation to take hold.
Please don’t use rat poison. Also, please try and help any animal that has an ailment — they can be helped: Here’s How These Alhambra Residents Handled a Sickly Coyote That Showed Up In Their Neighborhood.
Rats can be eliminated in a humane way. The best way is by exclusion and removing the attractants: plug up the holes in your home and remove/contain food sources. Within two weeks, they’ll leave. Alternatively, there are high-frequency devices which drive the animals away (but probably also the birds). Lastly, you can call a pest-removal service that uses humane traps. Please note that most private pest-management companies will either drown the rat or suffocate it to death with industrial strength carbon dioxide – both methods are extremely painful. The animal needs to be killed humanely.
To find a trapper in your area, please Google “humane trapper”. For rodent control alternatives, please visit www.wildcarebayarea.org/rodenticide or www.wildlife.ca.gov/Living-with-Wildlife/Rodenticides.