Animal Planet, long regarded as a gentle wildlife channel, is shedding its cute and cuddly image. The 11-year-old channel, owned by Discovery Communications, is one of the best-known brands on cable, but its ratings have stagnated for several years. On Feb. 3 the channel will start programming specifically for adults, scrapping its previous “something for everyone” style. “It made us unimportant to everyone,” said Marjorie Kaplan, who became general manager of Animal Planet last year. If the old Animal Planet was defined by a voice of God narrator — Ms. Kaplan mimicked it in a recent interview, putting on a...