Other substances that can poison animals besides rat poison?

Any substance that can kill many species of animals is by definition NOT eco-friendly. I hope you are not putting poison out in nature where it will kill more than your intended victims. If you kill native wildlife including birds, you can be fined or sent to prison. You might also kill animals that then eat the animals you poison (predators such as coyotes, bobcats, hawks, eagles, etc.) You might even inadvertently kill a neighbors pet or child. It is NEVER a good idea to put poison out into the ecosystem.