A Hunting Eagle???

[Kransha]

Well, eagles are too noble to be spies by definition. I believe he was a scout. When Legolas says..

"I wonder what that forebodes. It is far from the mountains."

...He most likely already knows what it forebodes, or could guess. The eagle could be a watcher in these dark times, far from his homeland to keep an eye on the shadows of Mordor or the lands that were under its evil veil. No hidden intents and purposes here as far as I can see, only some sensible symbolism in omnipresent aviary form.