On the eagles in LOTR and why they didn't just fly to Mount Doom: The strategy that the Fellowship decided on in Rivendell was to destroy the Ring in a mission of secrecy because Sauron did not know exactly where the Ring was. The eagles would've easily been seen flying towards Mordor and taken out by the Nazgul, sacrificing secrecy and drastically increasing the chances of the Ring being captured by enemy forces. Travelers on foot could easily sneak around and scout ahead, slipping by unnoticed - hobbits especially are renowned for being light on their feet and very quiet which is why Gandalf recruits Bilbo for Thorin's quest to enter Erebor. Eagles would've been spotted as far as Cirith Ungol where the watchmen for Mordor stand guard, giving Sauron's forces time to prepare and engage. Another thing: The Ring could not just be dropped into the caldera of Mount Doom, it had to be taken [i]into[/i] the Crack of Doom itself: the centre of Sauron’s power where the Ring was forged. The Crack of Doom was at the end of a tunnel that bored into the mountainside, and an eagle would not have been able to fit inside and a giant eagle sitting by the Crack of Doom (provided it could even get there) would be easily noticed. Finally, the eagles were generally dishonourable creatures who did not care for the affairs of mortal men. They only agreed to help Gandalf because he saved their leader who said he could call on them when needed.