Thorondor as a Maia???

[The Saucepan Man]

However, all sentient beings are either Children or Ainur-class/ealar ...

But what about the sentient animals such as the Eagles themselves, the Fox in LotR and the Ravens in the Hobbit? Assuming that there were sentient non-Maiar Eagles around in the First Age, could Thorondir (on the theory that he was a Maiar spirit incarnated in Eagle form) have mated with one of them? Or would they fall into the category of beings without a fea, making a union between any such creature and a good Maia spirit implausible?