Referring to the novel Fahrenheit 451... In the opening scene, why are the books compared to birds?

In the opening scene of Fahrenheit 451, Montag is in the process of burning a house full of books.  Montag notes that the burning books are “flapping pigeon-winged books [that] died on the porch and lawn of the house.  While the books went up in sparkling whirls and blew away on a wind turned dark with burning.”

To understand this metaphor, you need to picture what a pile of burning books would look like.  The pages are like the wings of a bird flapping in a burning pile.  Picture the pages of a book blowing in the wind and burning as if you opened the book’s spine and spread out the pages.  The ashes and burning pages take off to the sky like a flock of birds lifted off by the wind of the fire.  The remains of the books blow away with the wind much like birds would disappear into a dark sky.  Once the pages are burned, the books are just dead shells scattered around the house’s lawn. 

It is a powerful use of personification that Bradbury uses in the opening scene of the book.  He also describes the fire hose as a “python spitting its venomous kerosene upon the world.”  The literary device of personification gives these inanimate objects life, and therefore, makes the visual image more powerful by painting a picture of the scene for the reader.