In February of 2018, a gray fox was brought to the Sonoma County Wildlife Rescue. The fox appeared injured when it was found in a backyard in Glen Ellen. It was lying on its side, with back legs appearing immobile. The rehab facility provided supportive care but the fox died during the night. When the body was examined, no signs of trauma were found so the fox was sent to the Wildlife Investigations Lab to determine the cause of death. During necropsy it was found that the fox was carrying two fetuses. Tissues sent for analysis came back positive for bromethalin. Bromethalin is a rodenticide sold under a variety of trade names over the counter to control rats and mice. Labels specify that it must be placed in a bait station, but the wax blocks may be purchased separately. Bromethalin is a neurotoxicant, which explains the lack of mobility found in the fox.
In April of 2018, another gray fox was found dead in Ben Lomand in Santa Cruz County. When rescuers saw signs that she was lactating, they searched for her litter and were able to locate one of her kits. This kit was brought to Wildlife Center of Silicon Valley and successfully reared with other kits. The mother was sent to the Wildlife Investigations Lab to determine her cause of death. This fox had died from anticoagulant rodenticide intoxication. Four different anticoagulant rodenticides were found in her liver, three of which were second generation anticoagulants. These materials were made restricted use in California in 2014, meaning that they can only be used by professionals for control of mice and rats in and around buildings. They work by preventing the blood from clotting. At necropsy, this fox had blood in her spinal cavity and chest cavity. It is likely that she was exposed to the rodenticides when eating rodents.
Unfortunately, these cases are not rare. They serve to remind us that we can unintentionally harm wildlife with our pest control practices. For more information on rodent control that is safer for wildlife, please visit: