Owls Collateral Damage on Illegal Marijuana Farms

JAMIE CHEN / AGGIE

Increased rat poison in forest areas harms spotted owls and barred owls

The impact of anticoagulant rodenticide, commonly known as chronic rat poison, on unintended wildlife has mainly been studied in agricultural and urban settings. However, recent data has shown that the use of rat poison in remote forests has increased and is killing wildlife. A study led by UC Davis and the California Academy of Sciences has shown that illegal marijuana farms are the most likely source.

Mourad W. Gabriel, the lead author of the paper, is the executive director of the Integral Ecology Research Center and part of the Research Associate Faculty at the Karen C. Drayer Wildlife Health Center at UC Davis.

Previous research has demonstrated that rodenticides were extensively at trespass grow sites on public lands,” Gabriel said. “We wanted to investigate if avian species, that would be clear sentinels of secondary poisoning, were exposed to [rat poison]. Also, if these individuals sampled from private lands that were not associated with trespass growths were exposed, then what are the potential source points.”

The results show the environmental impact of illegal marijuana farms.

Illegal marijuana grow sites are unregulated and the use of large quantities of pesticides is likely having a very negative effect on wildlife populations,” said Robert Poppenga, a veterinary toxicologist at the CAHFS Toxicology Laboratory in the School of Veterinary Medicine at UC Davis. “The sites are often contaminated with a variety of pesticides and the costs associated with clean-up are substantial.”

One species heavily impacted is the northern spotted owl. This owl is listed under the Federal Endangered Species Act and was recently listed under the California Endangered Species Act. Barred owls have entered the critical habitat designed for the spotted owl and now compete for the same resources.

Rodenticide is just part of the problem, but one of the more readily measurable impacts,” said Jack Dumbacher, a curator of ornithology and mammalogy in the Institute of Biodiversity Science and Sustainability at the California Academy of Sciences. “Finding these toxins in barred owls suggests that it is an ecosystem-wide uptake, or, that the toxins are not just in rodents, but they are poisoning the entire food chain, right up [to Barred and Spotted owls]. Spotted owls are a very sensitive endangered species and this is a serious threat to a species that is already plummeting toward extinction.”

 

Written by: Kriti Varghese — science@theaggie.org