I have been puzzling with it as well.. And this is my conclusion:
It is a quest for Druid, and only Druids can summon Anzu the Raven god or what so ever.. This is done in heroic mode, in Sethekk Halls.. As far as I understood, by a lot of peeps, that quest is bugged..
Thats why it is now a part of a Hyjal chain..
PS: Look up "Reins of the Raven Lord" on thottbot.com
or "Anzu"