Definitely needed editing. Strange.
This is Newsweak. Wow. Their editing is no better than what you might find in a teen magazine, if that.
I would have worded it: “Montana Grizzly Bears killed due to strange behavior caused by highly pathogenic virus.”
Granted, it is three extra words, and I know brevity is a quality stressed by Strunk and White in their “Elements of Style” guide, but...that strikes me as being penny-wise and pound-foolish.