Aggressive Sparrows

What are farms meant to do? We have until recently had a healthy population of House Martins, Sand Martins, Swallows, Chaffinch and other small birds. Then we started to see House Sparrows move onto the premises approximately 5 years ago and have steadily watched them get rid of most of the other birds. Sand Martins were first - sparrows now live in their home, Swallows have had their nests invaded and the Sand Martins have had their babies thrown out of their nest last year. I have watched the Swallows returning this year and they stay about for a day or two but they are moving on as they are constantly harassed. We take great enjoyment watching our birds but the sparrows have changed the population out of all recognition. Magpies are also starting to be seen on our ground - they have never been here in the 80 years we have farmed here. Can we have a discussion on causes of this - I know there is no solution - but at a time when farmers are attacked for all sorts it is hard to see our bird populations decimated through no fault of ours.