I'm not having a sparrow war, but I did notice that there was a bird in my newest coop a few days ago. My mom is always putting out wild bird seed in feeders for the birds, so they don't usually go into the coops. The only thing that would bother me if they started frequenting the coop would be the risk of disease and pest transmission, just as you're worried about. The chickens do free range some, too, but my chickens generally chase the birds off if any try to land in the yard while they're out free ranging.
