Turkey vultures indicate rodenticide prevalence near Los Angeles, California, despite state-wide bans

Turkey Vultures (Cathartes aura) in southern California are still exposed to anticoagulant rodenticides (ARs) even though legislation was passed to drastically reduce the presence of these poisons across the state.

This is according to the short communication “Turkey Vultures (Cathartes aura) from Southern California are Exposed to Anticoagulant Rodenticides Despite Recent Bans,” recently published in the Journal of Raptor Research.

The harmful nature of these rodenticides is what led to their ban in California. If they persist, this could spell trouble for additional non-target wildlife species, including those with an endangered status like the Burrowing Owl (Athene cunicularia).

Anticoagulant rodenticides cause system failure in animals by interfering with the synthesis of vitamin K-dependent coagulation factors in the liver. This is true for rats as well as raptors. Of the non-target wildlife species that encounter ARs, raptors are disproportionately harmed because toxins accumulate as they move up the food web, reaching their highest levels in top predators.

In southern California there are three especially vulnerable raptor species for which this is of immediate concern: the Burrowing Owl (Athene cunicularia), White-tailed Kite (Elanus leucurus), and the well-known scavenging California Condor (Gymnogyps californianus), the latter of which already faces constant health risk from residual lead shot fragments inside carcasses on the landscape.

Turkey Vultures possess a suite of characteristics that make them uniquely representative of poison accumulation in their environments. They are more widely distributed than many of their raptor cousins, including the California Condor. They also cruise over large swaths of land encompassing many different habitats and consume a wide variety of prey items. These qualities make them important sentinels in the world of raptor toxicology. The field focused on identifying primary toxicants threatening raptor populations.

To investigate the prevalence of vulture exposure to eight different types of rodenticides, a team of researchers led by Drs. Peter Bloom, Miguel D. Saggese, and Andrea Bonisoli-Alquati trapped 27 Turkey Vultures in southern California near Anaheim between 2016 and 2021. The birds were fitted with wing-tags and their blood was sampled. All birds were subsequently released back into the wild.

Each was tested for first-generation ARs and second-generation ARs, the latter of which is thought to be more toxic than the former due to its higher strength and slower metabolic breakdown. The results showed that 11% of the vultures tested showed evidence of AR exposure. Although 27 birds is a small sample size, these findings suggest that if vultures are being exposed, other raptors probably are too.

“The presence of rodenticides in the blood of a few individuals is just the tip of the iceberg and demonstrates that these compounds are still out there. Even a small percentage of exposed wildlife should be considered a loss,” says Saggese, a faculty member at the College of Veterinary Medicine at Western University of Health Sciences.

The researchers recommend future studies focused on comparative analysis of both liver and blood samples from Turkey Vultures because liver, while difficult to collect, provides a more accurate and timely snapshot of AR exposure. Rehabilitation centers care for many birds that eventually succumb to their afflictions, providing a potential source for ground truthing this methodology.

Furthermore, the team emphasizes the importance of continuing to monitor AR exposure in Californian Turkey Vultures and keeping an eye on the adherence of pest control companies to the active legislature regarding rodenticide use.