If birds get tangle trap on them they will most likely die. I have seen a gooed up bird hopping on the turf near a tree where tangle trap was fairly horizontally applied. I was able to clean the bird's feathers with a solvent but it would have died otherwise. If you don't want to kill a lot of birds I suggest removing lower branches.
[NAFEX] Coating branches with tangletrap,
Alan Haigh, 05/21/2009