A mother polar bear and her cub hunt for seal pups, an increasingly difficult task as Arctic winters warm and ice disappears. “Nature” gets up close to polar bears and their ancestor, the grizzly, to see how a changing climate is affecting both species when “Arctic Bears” premieres on PBS Sunday, February 17 at 8 p.m. (check local listings). br br Academy Award-winning actor F. Murray Abraham narrates the film, part of the 26th season of the Peabody and Emmy award-winning series produced by ThirteenWNET New York for PBS. Major support provided by Canon U.S.A. Inc., Toyota, and the Corporation for Public Broadcasting.