Originally Posted by Psysquid

That's not really an explanation. It's just a statement. Still, it works for me. It does not contradict anything.

Sirius didn't have a chance to tell Hedwig anything, but she still managed to find him.
She found Harry, too, in PoA. Tom of the Leaky Cauldron was impressed -- "Smart Owl you've got there..." No one told her that Harry was there. She just somehow knew.

It's what Hedwig does. It's what Dobby does. It's what Fawkes does, and we don't really need an explanation.