Werner Herzog’s characteristic fascination with the darker aspects of nature and humanity informs this documentary about Timothy Treadwell, a self-styled environmentalist who spent 13 summers among the grizzly bears in Katmai National Park and Reserve in Alaska before he and his girlfriend were mauled to death in 2003. A failed actor, Treadwell was fastidious in videotaping his annual sojourns, and the footage becomes a bizarre performance piece, recording not only his good intentions but his narcissistic mania in the presence of his beloved bears. Like so much of Herzog’s work, both narrative and documentary, this is an engrossing look at obsessive behavior gone terribly awry.