Edit:
Sometimes a chicken will release its feathers when stressed (as in predator attacks)The predator will get a mouth full of feathers and the chicken will escape.Except in this case the chicken was terrified and couldn't run & hide.It died of a heart attack I suspect.
If I understand correctly there is bear scat in your yard and landscaping disturbed so I assume the chickens saw & heard everything.My guess is the 2 chickens ran inside the coop and the roosters being bolder stayed out.One thing that happens when chicken become frightened and stressed is is...