I'm gonna toss my two cents in.
An owl.
The reasoning:
Owls have a rep as being wise, and mikos need to carry great knowledge (as they travel, help, heal, etc).
Owls are generally quiet (but not always), and Kikyo is as well.
When observed, owls seem to take their time, watching things with a slow steady grace, not making sudden movements. This gives the impression of deep thought, until it is time to act. Kikyo usually is shown sitting and staring off into the distance, deep in thought, but can move swiftly when it is time to strike.
This is just my opinion, nothing more.