Chemicals used by marijuana growers may poison forest animals
Widespread rat poison on California public lands poses a threat to declining carnivores called fishers, according to a new PLoS ONE study. The scientists suspect that people growing marijuana illegally in the area may be responsible for spreading the chemicals.
Researchers have found rat poison exposure in wild animals before, but such cases were thought to occur mainly near farms and cities. The fisher (Martes pennanti) seems an unlikely target, since it lives in remote forests.
The team caught fishers in northern California and the Sierra Nevada mountains, outfitted the animals with radiocollars, and released them back into the wild. When a fisher died, the corpse was collected and submitted it to a pathologist for examination. Researchers also tested the animals for seven types of rat poison.
Seventy-nine percent of the fishers showed signs of rat poison exposure, the authors report. While many of the animals were killed by diseases, predators, or cars, four fishers appeared to have died from rat poison.
Fishers may be preying on rodents poisoned with the chemicals or eating the poisoned bait itself, since flavors such as bacon and peanut butter are often added to entice rats. Even if the rat poison doesn’t kill a fisher, it could weaken the animal by interfering with blood clotting. A fisher wounded in a fight with prey, for example, might die more easily.
One possible source of the poison is “the emerging spread of illegal marijuana cultivation within California public and private lands,” the authors speculate. Growers often place rat poison near marijuana plants and irrigation lines to keep rodents away. The chemicals could affect not just fishers but also red foxes, wolverines, and other carnivores. — Roberta Kwok | 16 July 2012
Source: Gabriel, M.W. et al. 2012. Anticoagulant rodenticides on our public and community lands: Spatial distribution of exposure and poisoning of a rare forest carnivore. PLoS ONE doi: 10.1371/journal.pone.0040163.
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