As i was drinking my coffee this morning i observed something i hadn't noticed before. The birds that were soaring had their wings in a positive dihedral. The birds that were flying near and into trees had their wings in a negative dihedral position. I assume that for simple soaring the positive dihedral keeps them stable and level. Then for rapid turning faster roll maneuvering, the negative dihedral position is easier for them. Of course i could be wrong but it makes sense.