There is an effort to try and reintroduce the Mexican Gray Wolf into a mountain range just south of the U.S.-Mexico border.
They are trying to re-establish the endangered species.
A rep from a group that supported the wolf reintroduction said:
"They've been working for decades for this reintroduction so obviously this is setback, but my assumption and hope is that they will continue and make it successful."
The poison was found to be warfarin, which is a rat poison.
Mexican authorities are looking into how the wolves ended up ingesting the poison.
There are farmers and ranchers who don't want to see more wolves running around, eating their sheep and doing other wolfy mischief.
The organizations trying to save the wolves still plan to keep moving forward with their efforts to shore up the gray wolf numbers.