I was reading a post on Mary's blog where she was bemoaning the invasion of her garden of a pair of House Sparrow's. One of the readers of her blog said that the only use for them was as Hawk food and that she could trap them for use at a raptor centre (I would like Jan to take a deep breath at this point and calm down ;) ).
This is a common view with introduced species, you read it here with the Grey Squirrel and the Ruddy Duck.
For those of you who aren't aware the House Sparrow was introduced as pest control in a number of US cities in the 1870's. Within a decade the introduction was regarded as a disaster (well that is a surprise). Today the Sparrow is one of North America's most abundant birds and is one of three (Rock Dove and Eurasian Starling being the others) it's legal to kill.
Apparently, well its says so on wikipedia, House Sparrows kill adult Bluebirds and other native cavity nesters and their young, smash their eggs, and take over their nesting sites, and as such are major factors in the decline of bluebirds and other native cavity nesters in North America. The House Sparrow is smaller than the native birds with which it competes, it is impossible to keep them out of nest boxes built for many native birds. Apparently the native birds are less aggressive.
The problem is what do you do with introductions? Is it realistic to remove all House Sparrows et al ? There are 150 million of them in North America. My guess is nothing, we have to accept that we have upset the natural balance and let nature take its course. A new natural balance will be reached. It may not be one we like but I don't see any other realistic option.
I think it just goes to show we should stop meddling.