|P.colchicus male - hybrid swarm type|
|P.colchicus female (UK)|
Common Pheasants were first introduced outside their natural range by the Romans as sporting and food animals, and it is possible they introduced it to Britain. In the British climate Common Pheasants can have trouble in raising chicks, which are sensitive to rain, and if any population established the numbers probably stayed low. Later introductions in the Norman period were probably more successful, but the massive deforestation in lowland Britain during the Middle Ages reduced the population to a few remnants. From the 17th century onwards however, government encouraged reforestation projects (timber was needed for the navy) and an increase in management of the countryside for hunting raised their numbers again.
In the 19th century, the rearing and shooting of pheasants became a major industry, and part of the lifestyle of anyone with the money and time to afford it (much like golf). Pheasants may be shot on driven shoots, the most labor-intensive kind, where beaters flush the birds from cover to fly towards the guns who remain at a fixed position, or rough shooting, where a small group of hunters walk a route looking for the pheasants to be flushed by a gundog.
To compensate for the high mortality and nest predation of wild pheasants, vast numbers are released each year a few months before the start of the hunting season on 1st October. Woodlands managed for the benefit of pheasant shooting also benefit a great deal of other wildlife, particularly songbirds, as habitat that provides good food and cover for pheasants also benefits them. In Britain, the Game and Wildlife Conservation Trust (formerly the Game Conservancy) has done a lot of research on the best habitats and management regimes for pheasants and other gamebirds, and their website is a very useful source of information. The various research articles can be found here: http://www.gwct.org.uk/research__surveys/species_research/default.asp
Outside the UK, Common Pheasants are introduced across western Europe, North America, Chile, Tasmania, and New Zealand, and unsuccessful attempts have been made elsewhere. What affect they may have had on local species in these areas is not always clear, and probably depends on whether there is a local ecological equivalent or not.
As well as Common Pheasant, a few other species have been introduced to the UK, mostly with limited success. I will cover these next week.
(images from wikipedia)