never heard of it, string and birds usually don't mix, they can get tangled, but not really sure what you talking about though.
I have used soft nerf balls and gently lob them up in their direction to get them flying again, or you can use a flag you wave in the air to keep them flying. then they need to be hungry so they just trap in right away seems to work for me, not always easy to do, but if they are hungry they should just shoot in to get some food.