The Unlearned Lessons of DDT

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Beachwood Canyon resident Allison Brooker recently received a call from one of her neighbors about a distressed owl sitting in her yard. Allison knew from experience that owls needed quick rescue. After snapping a photo, Allison called a friend to help her and notified the California Wildlife Center that she would be bringing the owl in for treatment. Her friend arrived bringing a box and towel to help gently corral and transport it to the center.

Ten minutes after the photo was taken, however, the owl died.

Allison’s rescue effort then turned into a disposal exercise. She took the owl to her veterinarian for cremation, and posted pics on Nextdoor. This is when Friends of Griffith Park stepped in.

Hearing about the situation, FoGP president, Gerry Hans realized the owl should be tested for rodenticides and contacted Allison who rushed back to the vet’s office to retrieve the owl carcass. She then passed it along to Gerry who shipped the remains to UC Davis Veterinary Medicine’s California Health, Food and Safety (CAHFS) lab.

A thorough workup at CAHFS includes necropsy, histological work, and lab analyses for heavy metals and anticoagulants. Because Griffith Park is surrounded by residential zones, FoGP has been sending dead animals to this lab for testing to determine cause, especially when there is no obvious reason for the animal’s demise. So far, two coyotes, a fox and a squirrel have been tested at UC Davis with all returning positive results for anticoagulant rodenticide poisoning.

Birds, however, present a more difficult challenge since normally they’re not found quickly enough to extract sufficient liver tissue for the lab work.

As Gerry suspected, the female juvenile owl did have anticoagulants in its body. In fact, tests showed extremely high levels of difethialone, a potent “second generation” rodenticide. The necropsy showed no fractures, no skin penetrations, but there was hemorrhaging (bleeding) in muscle tissue. The combination of all aspects studied resulted in a conclusive cause of death as anticoagulant intoxication. Likely, a mouse or rat ate the poison from a “bait box” and then the slow moving rodent was nabbed by the owl.

While second generation rodenticides were removed from store shelves in California in 2014, pest control companies, such as Orkin and EcoLab use them routinely, often without customers realizing these dangerous poisons are becoming prevalent in the global ecological food chain. Second generation rodenticides kill raptors, bobcats and other wildlife that help keep rodents in check, an ironic twist of Mother Nature’s best work!

FoGP and other environmental organizations have been raising the alarm for quite some time since this struggle is reminiscent of the ban of DDT use across the globe. After three decades of use, DDT was found to imperil many species, particularly raptors such as bald eagles, California condors and peregrine falcons. It’s also been found in various aquatic species which moves up the food chain through consumption. Although DDT use was finally banned in 1972, California condors failed to reproduce in the wild due to thin egg shells, and nearly faced extinction as a result.

A few facts about anticoagulants…

  • Anticoagulants have long half-lives that bioaccumulate throughout the food web, just like DDT. These poisons travel up the food chain to the top predators. Many studies show exposure at rates of 85% and higher in various species randomly sampled.
  • Anticoagulants have shown to produce non-lethal and not readily noticeable effects, just like DDT. For example, suppression of immune response which ultimately decreases life expectancy has been scientifically documented in bobcats.
  • Species are threatened by anticoagulants in California, just like DDT. Nearly 100 deceased endangered-listed San Joaquin kit fox were tested positive for anticoagulant exposure.
  • Anticoagulants are found across the animal kingdom, just like DDT. Studies show them also in invertebrates (such as snail and insects), fish, ungulates and reptiles.

These are the reasons for the proposed State legislation AB 1788, which is now sidetracked for enactment due to COVID-19 priorities. In the meantime, Governor Newsom can act by supporting a moratorium on the use of these products. The process for AB 1788 should play out, but in the meantime, we don’t want continued damage to wildlife and the entire ecosytem.

Ask Governor Newsom to Declare a Moratorium on Rodenticides

Photos: Allison Brooker
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