I think we can see that with multiple large producers currently have problems with the bird flu, that sealing up buildings and attempting the keep birds safe doesn't actually work out.
It's always recommended to do all you can to keep wild birds away from your flock because they can bring in diseases, but so can the wind.
That being said I can't keep the sparrows out of my large shed, just keep them from nesting in it. I feed wild birds during the winter and encourage them in...