Arash, hope I'm not taking too much of your time, but is that considering image stabilization? If it is, does that mean un-stabilized I would be shooting for 1/4,000s or 1/8,000s, something like that?
I think Arash was referring to the SS necessary for sharp frames when hand holding. His statement had nothing to do with IS vs. no IS. You almost never need a SS faster than 1/4000 to do most any kind of bird photography.