They almost literally never collide.It struck me as an odd word order to use. Surely it should be
They literally almost never collide.What's modifying what here? Well, in Dawkins' sentence (let's label it A), almost is modifying literally:
They [[almost literally] never] collideHe means that they rarely collide; he can't say that they literally never collide, but never is used in an almost literal sense here. OK, makes sense.
Or is it that almost modifies literally never?:
They [almost [literally never]] collideThat second one seems odd to me. I don't think it's possible for that to be the structure - I can't even quite see what it would mean. So it's the first then, with literally qualified by almost, and the whole constituent modifying never. The birds, in their massive flocks, are very good at not colliding. It's not quite true to say that they literally never collide, but they almost literally never do. Ignoring the fact that this is a slightly hyperbolic and quite superfluous use of literally, it's perfectly sound.
But if he had written sentence B instead, the modificational relations are clear: as we can't say that literally can modify almost, literally modifies the constituent almost never.
They [literally [almost never]] collide.Literally is used, as it so often is, for emphasis: he means they almost never collide, and he means that literally. He's not exaggerating. They really do almost never collide.
Syntactically, both are OK. Stylistically, I know which I prefer.