Late last year, a grey fox died of rodenticide poisoning near federal park land in Inverness, according to Point Reyes National Seashore wildlife biologist Dave Press. The death, and the suspected poisoning of a northern spotted owl in the same area, spurred Mr. Press to partner with the California Department of Fish and Wildlife to raise awareness of the dangers rodenticide can have on local wildlife. “People are trying to kill pesky rats but don’t realize the other impacts,” Mr. Press said. Now Fish and Wildlife is working on a flyer to distribute locally to warn people about the unintended impacts of rodenticide. The issue arose after an Inverness man called the seashore, alerting staffers to a dead gray fox near his home; there were no obvious external injuries on the animal, which otherwise appeared healthy. “When you find an animal that otherwise seems in good health, it’s good to look into what’s going on,” Mr. Press said. Lab tests proved that anticoagulants from rodenticide—specifically brodifacoum, bromadiolone and difethialone—had caused internal bleeding. Mr. Press also suspects that rodenticide may have caused the death of a northern spotted owl, a federally endangered species, discovered in the same area a month before the fox was found. (The owl was never tested.) Stella McMillin, a senior environmental scientist with Fish and Wildlife who is creating flyers to distribute locally, said there were 45 cases of identified wildlife poisonings in California in 2015, including a great horned owl and a Swainson’s hawk. And, she said, “I’m sure the actual number is a lot higher.” Ms. McMillin noted that since the anticoagulant that killed the fox in Inverness became restricted to professionals in 2013, a pest control professional had likely used it. Fish and Wildlife, she said, encourages homeowners to learn about which methods pest control companies use and to focus on blocking rodents from entering homes and setting traps for those that are inside.