Pheasants are an invasive species from China, but they are not very invasive like Burmese Pythons and Iguanas in Florida. In fact, they do not really thrive anywhere in the USA, but they make for good sport and good dog-training where they are found. Friend sent me this pic from a Pheasant hunt in northern Montana a couple of weeks ago (it would have been full of bison and grouse in past years):