OregonLive has a solid write up on a mule deer study conducted by state wildlife officials over the last five years.
The state study was conducted from Bend to the California border. Of 500 mule deer fitted with radio-collars between July 2005 and last January, 128 died during the research. Of those, poachers killed 19 and hunters legally shot 21. Cougars killed 15 and eight were hit and killed by cars. Of the rest, five succumbed to coyotes, disease claimed five and four died while tangled in fences or from some other accident ... Biologists listed 51 as "cause of death unknown," but poachers could have taken some of those, he said. "Sometimes we just find the radio collar laying out in the sagebrush,"