Take the Blue-feathered Necklace to Nara Wildmane.
While I do possess much knowledge about the owlbeasts you defeated in Winterspring, I am not very learned on the subject of the magics they wield. But I do believe I know of one that would be able to examine the necklace and most likely tell you what it is.
Nara Wildmane in Thunder Bluff is an expert in this field; see her. Good luck, [player].