At least three Santa Cruz bobcats have died in the last four months of complications related to ingestion of rodent poisons, according to local news reports. The three, all found dead in the vicinity of the UC Santa Cruz Arboretum, had high amounts of anticoagulants used in rodent poisons in their bloodstreams.
Two of the cats were actually killed by cars on Empire Grade Road, one in September and on in early December, but each had enough anticoagulants in their bloodstreams that it's likely they were too weak or disoriented to avoid the vehicles, a state biologist suggested. Another bobcat, who died on the Arboretum grounds on September 3, succumbed directly to the effects of the poisons.
UCSC uses non-toxic methods of rodent control on the arboretum grounds, and the University's public affairs office told the Santa Cruz Sentinel that most of the neighbors in the immediate vicinity deny using anticoagulant rat poisons as well.
"An animal that's been exposed to anticoagulants is basically bleeding out and slowing down because it's losing blood," California Department of Fish and Wildlife scientists Stella McMillin told the Sentinel. "That can have a lot of behavioral impacts, such as not being able to avoid predation and not being able to avoid vehicles."
So called second-generation rodent poisons containing the anticoagulant brodifacoum were banned for household use last July by California's Department of Pesticide Regulation. However, the rodenticides affected by that ban are still available for professional or agricultural use.
All three bobcats' blood samples also tested positive for the rodenticide diphacinone, which is not affected by last year's ban.
Anticoagulant rat poisons kill by inhibiting blood clotting; animals that consume the poisons tend to die through internal hemorrhaging. The active ingredients in the poisons aren't quickly broken down by the target animals, and the poisons work slowly enough that a rodent can consume many times a lethal dose before feeling the ill effects. That means that predators or scavengers that eat a poisoned rat can ingest dangerous amounts of the poisons. Rat poisons have been documented to cause such incidental injury to a wide range of animals from bobcats and mountain lions to owls, hawks, eagles and other raptors, as well as family pets.
As bobcats generally range over relatively small territories of a few square miles, the California Department of Fish and Wildlife will be distributing flyers in the neighborhood to warn neighbors of the risks to wildlife of improper use of rat poisons. It's not just bobcats at risk: the nearby foothills of the Santa Cruz Mountains are home to mountain lions as well.
For the record: an earlier version of this piece stated that UCSC, not CDFW, was reaching out to neighbors to warn them about the effects of rat poisons on wildlife. We regret the error.