Why Are Owls Dying Near Marijuana Farms?

The northern spotted owl, currently petitioned to be added to the list of threatened and endangered US species. Photo credit UC Davis

Due to their protected status, the authors only collected spotted owl carcasses that they happened upon while out in the field. The barred owls were collected for use as "surrogates" for spotted owls because they compete against spotted owls for territory and food. So, even though only 10 spotted owls were collected, it is likely they would be infected with ARs at the same rate as barred owls.

Study co-author Jack Dumbacher and owl collection 5 at the California Academy of Sciences. © 2017 California Academy of Sciences

Somewhat hearteningly, necropsies of the northern spotted owl carcasses showed that none died directly from AR poisoning, and since tissue samples from barred owls were collected from living specimens, the tissue levels must have been sublethal in them as well. However, the authors speculate that the effects of even low-level poisoning are likely to make recovery of spotted owls even more difficult.

Juvenile northern spotted owls. John P Dumbacher © 2017 California Academy of Sciences

Mourad’s team also have evidence that ARs are leading to the deaths of bobcats, mountain lions, coyotes, and bears, suggesting that the careless actions of illegal growers are impacting not only a few select species, but much of the forest ecosystem.

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