So, the Eagles. Rather than point to one of the many treatises on the subject I'll just give my own brief response. There are, from recollection, four incidences in the Hobbit and Lord of the Rings where the Eagles turn up. The first is when the Dwarves and Hobbit are stuck in the trees when being chased by the goblins and wargs, the second is "high and far off" in the Battle of the Five Armies, the third is when Gwaihir the Windlord rescues Gandalf from the pinnacle of Orthanc and the final time is at the Black Gate, when they join in the fight and are conveniently to hand to bear Gandalf to Mount Doom to save Frodo and Sam from being engulfed in the lava flow following the destruction of the Ring. Of all of these, only the final one could legitimately be considered a Deus ex Machina.
The first event had many other options for resolution. Gandalf's use of the flaming pine cones could have worked, driving the Wargs mad with fear. In fact, this was precisely what was happening until the goblins appeared and used the flames to set the trees alight. Even then, there was no cliff face, no impossible escape. In fact, the reverse is true. Tolkien deliberately writes a scenario that requires the Eagles, because he needs to use them for the next part of the story. Having been "rescued" by the Eagles, Bilbo is not even sure if they are safe or are now prisoners. It turns out, in true Fairy tale fashion, that Gandalf once cured the Lord of the Eagles (unnamed at this point) of an arrow wound. The Eagles drop them at the Carrock in time to meet Beorn, thus safely getting thirteen Dwarves, a Hobbit and a Wizard across the Anduin river without needing boats. (A fact that is conveniently ignored on the return journey).
The second event is mentioned in passing before Bilbo is knocked out and misses the entire Battle of the Five Armies, which is described in a total of two paragraphs and the Eagles are merely another set of combatants, and do not save the day. The tide of the battle is turned rather by the emergence of the Company of Thorin from Erebor falling upon the rearguard of Bolg's army, with Thorin, Kili and Fili all dying in the assault on Bolg. In fact, if there is a Deus ex Machina here, its Beorn, who arrives in Bear form and kills Bolg.
The third event happens as a result of Saruman's contempt of "Radagast the bird tamer, Radagast the fool". Because Saruman ignored Radagast he did not realise that Gandalf had asked Radagast to send word to him in Isengard of any news. Gwaihir the Windlord did not come to rescue Gandalf, but to bear tidings. Saruman's treachery was at that time know to none. When Gwaihir found Gandalf imprisoned alone on the pinnacle of Orthanc he carried him to safety in Rohan. So, again, no Deus ex Machina here.
The final appearance of the Eagles is at the Black Gate, when the armies of Gondor are in an unwinnable battle, sacrificing themselves to allow Frodo and Sam the chance of making it to the Sammauth Naur undetected. There is no victory to be had in this battle. They are vastly outnumbered. The destruction of the Ring causes Barad Dur to fall and Sauron's will to dominate is removed from his armies, which causes them to lose their shape and structure and their confidence. They begin to rout, killing each other in their desperation to get away and the eruption of Orodruin causes earthquakes which open great fissures in the earth across the plain of Gorgoroth where the vast bulk of Saurons armies are still mobilising. Again, the Eagles appear high and far off as Pippin loses consciousness, in a deliberate homage to Bilbo's moment so many years before. Again, the Eagles do not turn the tide of battle. However, they are conveniently to hand to rescue Frodo and Sam from the lava. However, once again, this is by design, not lack of options. There were many ways Tolkien could have rewritten that scene to save Frodo and Sam without needing the Eagles, but he wanted that Epic feel to the final scenes. Is that a flaw in a writer of high fantasy? I don't think so. Its a strength. A writer who knows how to craft a tale of grandeur and myth.
Now, why PJ chose to change every one of those scenes? Thats a subject for a different post!
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