It hasn't been mentioned but I find using 9 point focus works better for BIF.
You got the point! 3-D tracking is good for the BIF if the back ground is simple and clear of other distracting object. If the bird is flying on top of something like trees, I will use the 9 point dynamic area, it will give the camera less confusing to focusing.
Do you find that 3D works equally well for subjects moving in lateral as well as perpendicular planes?
Focus is more of a factor with subjects moving towards or away from the camera, not so much left to right or right to left. Panning is more an issue in the latter to help reduce motion blur. So much to know, so little time.