As the crow flies

It’s eighteen miles to Denver as the crow flies.
It’s also eighteen miles to Denver as the crow walks.
Or drives. Or rides a bus. Or rides a bicycle.
Why don’t I say it’s eighteen miles to Denver and leave out the crow reference?
I don’t know. It just sounds better that way.
Makes me sound like a country boy.
I guess if I wanted to sound like an Australian, I’d say 18 miles as the kangaroo hops.
Except that they use metric down there.
Do they have crows down there?
And how far is it from there to Denver?