Seven elk were found dead in the Boise foothills on Tuesday after apparent poisoning from eating Japanese yew, said Idaho Fish & Game officer Bill London.
Five of the elk were found by a sportsman near the area of Table Rock Road and Wild Horse Lane, London said.
“He thought it was suspicious for this time of year,” London said. “And he was right. Their body condition was not that of a normal winter kill. They should not be dying of cold weather right now.”
The elk had been dead about five days, determined conservation officer Ben Cadwallader, who is leading the investigation, and their bodies were already being fed on by predators.
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Necropsies of the animals’ rumen — partially digested food that travels through an elk’s four stomachs like a cow’s cud — identified the culprit as Japanese yew, a popular but poisonous ornamental plant.
As the officers worked on the first five elk, a homeowner on Wild Horse Lane told Cadwallader and London that another elk had died on his property over the weekend. That animal’s necropsy also turned up Japanese yew as the cause of death.
The plant, like other members of the yew family, is highly poisonous. Just half a cup can kill a full-grown elk, London said, and it’s poisonous to humans and to domesticated animals like horses and dogs, too. In fact, it’s possible for dogs to get secondary poisoning by ingesting the stomach contents of animals that died of yew poisoning.
The problem is not new in Idaho. In December, Japanese yew killed some cattle near Burley. Last January, more than a dozen elk died near Hailey after eating the plant. That prompted Blaine County to outlaw the Japanese yew, a measure that London said is “part of a discussion right now” for the Treasure Valley.
London said that kind of measure is out of the hands of Fish & Game, and he’s not sure if it would drum up support in the Treasure Valley. He advocated for addressing part of the problem by talking to local plant nurseries that sell the yew.
For now, officials are urging people in the Foothills region where the elk died to canvass their property and destroy any Japanese yew they might find. Having never removed the plant himself, London recommended taking a chainsaw to the plant and dealing with any potential remaining roots when the ground has thawed.
Plants that are removed should be discarded at a landfill so that they won’t be eaten by animals, London added.
Exacerbating the problem, he said, is a resident whose “heart is in the right place” who has been putting out hay near the homes where the dead elk were found yesterday.
“Their heart’s in the right place, but they’re hurting the elk,” he said.
The problem is twofold: The elks’ stomach bacteria at this time of year are not set up to digest hay. That can lead to an animal with a full stomach dying of starvation, London said. In addition, setting out hay for wild animals lures them to residential areas where poisonous plants like yew are present, and where interactions with people, pets or cars can be harmful.