Not commenting on USAir 1549 since I have no idea on the visibility or what they could or could not see.

Most birds or bird flocks are too hard to see until it's too late. If a bird or flock is seen and it appears to be a danger, a simple pull up to miss it by a few feet is about all we can do. It's a good reason to leave the cabin crew in their seats until above 10,000. Mostly it's just the "Big sky, little bird" theory.

I've plowed through flocks on the takeoff roll (aborted) and landing roll-out. Nothing to do except go through them. Pigeons and dove are really, really stupid birds.