The unnamed eagle is attested in both the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson, while Veðrfölnir is solely attested in the Prose Edda. In both the Poetic Edda and the Prose Edda, the squirrel Ratatoskr carries messages between the unnamed eagle and Nidhöggr, the wyrm that resides below the world tree. Scholars have proposed theories about the implications of the birds.
The eagle is again attested in chapter 16 of the Prose Edda book Gylfaginning, yet here with the company of Veðrfölnir. In the chapter, Gangleri (described as king Gylfi in disguise) asks the enthroned figure of High what other notable facts there are to know about Yggdrasil. High responds (Veðrfölnir is here anglicized as Vedrfolnir):
'There is much to be told. An eagle sits at the top of the ash, and it has knowledge of many things. Between its eyes sits the hawk called Vedrfolnir [...]. The squirrel called Ratatosk runs up and down the ash. He tells slanderous gossip, provoking the eagle and Nidhogg.'