Theres certainly a number of “pheasant farms” around, with regular big bags – and I’ve worked on a few as a student, however as with everything its a complex equation, harsh winters will undoubtably take a toll on the survival ratios and in central scotland the winter conditions would be a significant factor – at the same time there’s a tendency for the birds to be less active, staying in the areas of cover more. However its unlikely that a pure wild bird population would be significantly less effected %age wise than released birds, there’s going to be a heavy toll regardless of their source – its in any good estates interest to keep feeding through the winter and the planting of cover crops like kale and maize, plus supplementary feeding, will clearly be beneficial to both the pheasant and other bird species winter survival – without the game shooting there’s no reason to put down the winter food, so overall I’d argue that the survival would probably be even lower without the influence of shoots.
The real wild shoots are a pretty spectacular place to be, the effort put into creating a wildlife friendly environment is huge – the bags are much, much smaller and the birds often a lot harder to shoot (older/wider/fitter/faster) – it would be nice to see more all wild shoots, but they are bloody difficult to do right, and very expensive to run – unfortunately a lot of the people who go game shooting are there for silly corporate entertainment crap and social climbing rather than a real love of the sport and wildlife, and they are fascinated by big bags and easy birds, ultimately its often these “punters” that pay for the estate and in the grand scheme of things its unfortunately better for the countryside and the other wildlife to have the pheasant farms than sterile agro-environments with bare canopy woodland with no copses, hedges or winter cover crops.