July 4, 2020 – In late April, a dead owl was found on a nature preserve in San Luis Obispo County. CDFW’s Wildlife Investigations Lab (WIL) performed the necropsy and found excessive bleeding on the owl’s leg and abdomen. With no associated wound or apparent trauma, additional toxicology testing was performed. Cause of death: fatal poisoning by anticoagulant rodenticides, chemical agents used for rodent control. For the WIL, it was the thirteenth raptor death by anticoagulant rodenticides since August 2019.
In a four-year study conducted by WIL biologists investigating the causes of mortality for hundreds of raptors – and 15 raptor species – across the state, more than 80 percent had been exposed to anticoagulant rodenticides. Roughly one-quarter of those raptor deaths were fatal poisonings directly attributed to anticoagulants.
In a two-year statewide study, the WIL found that 96 percent of necropsied mountain lions showed non-fatal exposure to anticoagulant rodenticides. Almost one-third of those lions had been exposed to at least four different types of anticoagulants.
Throughout California, chemical baits used to control rodents have injured and killed non-target wild animals and pets. Anticoagulant rodenticides work by preventing blood clotting in the animals that consume it resulting in fatal bleeding. Predatory and scavenging birds along with mammals like raccoons, bobcats, foxes, skunks and coyotes that have eaten rodents which have consumed the bait can also be fatally poisoned.
“It’s troubling seeing an otherwise healthy animal die from anticoagulant rodenticides. In many cases these deaths may be preventable.” said Krysta Rogers, an environmental scientist and the WIL’s lead avian mortality investigator.
In 2014, California restricted the use of second-generation anticoagulant rodenticides with several chemicals known to be harmful to wildlife, pets, children and the environment. Additionally, the U.S. Environmental Protection Agency has implemented a national ban on consumer use of rodenticide products that do not meet revised safety requirements. However, products containing second-generation anticoagulant rodenticides can still be used by licensed exterminators.
Despite the restrictions, the WIL says that wildlife is still being exposed to both first-generation and second-generation anticoagulant rodenticides. CDFW would like to remind the public of the measures that can be taken to help reduce anticoagulant rodenticide exposure in non-target wildlife.
The best way to protect wildlife is to use non-chemical means of rodent control. Habitat modification is an effective means of preventing rodents from inhabiting property. For example, many rodents like tall grass for cover. Mowing grass to no more than two inches makes it less appealing. Like most animals, rodents go where they feel safe and where food is available. The easiest way to discourage rodents from inhabiting property is to remove food sources and remove or modify anything that provides cover.
These simple actions can help:
- Keep your home and yard neat and clean.
- Keep tree branches and vegetation at least a foot away from home and roof.
- Seal any holes on your home and roof where rodents can gain entry.
- Be aware that pet food, chicken feed and bird feeders will attract rodents.
- Remove objects and plants that rodents can hide under such as wood piles, debris, construction waste, vegetation and ground-covering vines like ivy.
- Pick up fruit that has fallen from trees as soon as possible.
- Secure your garbage in a tightly sealed can.
- Seal water leaks and remove standing water that may attract unwelcome animals.
For more information, visit the rodenticides page on CDFW’s website.
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