Answer: She smoked and slept around

Question: Why did the birds attack Melanie Daniels (played oh-so-coolly by Tippi Hedren) in Alfred Hitchcock's classic? This simple fact seems to have escaped Mandalay Pictures president Cathy Schulman, who's planning to remake the movie with a very of-the-moment environmental twist, she says: "In the original, the birds just showed up, and it was kind of like, why are the birds here? This time, there's a reason why they're here and (people) have had something to do with it. There's an environmental slant." [Source: Defamer]