Our directory of things of interest

University Directory

Weed killers: endangered owls in California

Weed killers: endangered owls in California
01 Mar
2018
Threatened Californian owls are suffering from digesting rat poison administered to the state’s thousands of marijuana farms

Marijuana is proving to be a health hazard, although not for the reasons one would assume. Since the start of the year, the private cultivation of marijuana crops has been legal in California, making it the fifth US state to permit the practice. Business is booming; Humboldt County alone, in the north of the state, is home to at least 4,500 – and potentially as many as 15,000 – plantations, and there is an expectation that numbers will continue to rise. However, at present the majority of these remain unlicensed and unregulated, even despite the recent legalisation passing.

Recent studies on owls found deceased in remote locations across Humboldt and neighbouring Mendocino and Del Norte Counties is focusing attention on the ecological impact of these farms. For example, 70 per cent of northern spotted owls – which are in decline in both range and population, and are consequently listed as ‘threatened’ under the Endangered Species Act – tested positive for various anticoagulant rodenticides, utilised to control rat populations within these farms.

Jack Dumbacher and owl collection 5 2017 California Academy of Sciences.jpg

By preventing the recycling of vitamin K, rodenticides cause a series of clotting and coagulation problems in both birds and mammals, followed by uncontrollable internal bleeding. For owls feeding naturally at forest edges, which unfortunately often also happen to mark the edges of these plantations, their dead rat dinners could potentially be their own death sentence (the studied birds in question were judged to have died of causes ranging from vehicle strikes to predation, not poison).

‘Sublethal anticoagulant rodenticide impacts vary from species to species, and also within individuals,’ explains Mourad Gabriel, a research faculty member at the UC Davis School of Veterinary Medicine. ‘We detected levels in our study that have been reported as benign in other owls, but other studies have shown these levels to be lethal, or having a negative impact in other owls or raptors. So as you can see it becomes a case-by-case scenario.’

Gabriel believes that, eventually, the legal market for marijuana will drive out these unregulated plantations and their overuse of rodenticides, but raises concerns about how long this might take. ‘We have empirical evidence of landscape contamination, and others have demonstrated habitat fragmentation,’ he adds. ‘The northern spotted owl is not increasing in population numbers, and there is consideration of up-listing this species to “endangered”.’

This was published in the March 2018 edition of Geographical magazine

geo line break v3

Free eBooks - Geographical Newsletter

Get the best of Geographical delivered straight to your inbox by signing up to our weekly newsletter and get a free collection of eBooks!

geo line break v3

Related items

NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in NATURE...

Wildlife

Invasive species are considered one of the greatest threats to…

Nature

Professor Steve Fletcher, director of the Global Plastics Policy Centre…

Wildlife

The international conservation agreement CITES is nearly half a century old.…

Wildlife

With Scotland’s salmon under threat, environmental groups are planting trees…

Oceans

As coastal development continues to grow, research begins to reveal the…

Wildlife

Research into rhesus macaques on a remote island finds that survivors of…

Climate

 The release of the latest IPCC report suggests it's 'now…

Wildlife

A new technique to collect animal DNA from thin air could…

Wildlife

As animal species decline, plants that rely on them to…

Nature

Calls to make ecocide a crime are gaining ground

Wildlife

In South Africa, a new wave of poaching has taken…

Tectonics

A volcanologist unpicks the devastating eruption of Hunga Tonga-Hunga Ha’apai

Oceans

Some areas of the ocean are richer in microplastics than…

Oceans

The ocean floor is home to rich deposits of metals…

Climate

The industry will only keep growing. Could algae help to…

Nature

A monumental effort is underway to map the world’s fungal…

Geophoto

In his project Black Dots, Nicholas JR White set out upon the…

Wildlife

China’s Amur tiger population is recovering, reflecting the country’s changing…

Climate

Scientists are pushing back against the notion that the food…

Geophoto

Xavi Bou's artistic visions of flight beguile the eye