They reason backwards: Birds evolved, therefore some poorly understood mindless processes must have driven them to evolve.
Watch how easy it is to tell a Darwinian story. If something exists and looks advantageous, it evolved.
Lang and Rice cite a number of articles to show that loss-of-function mutations are just a small minority of those found in studies of organisms.
Alas, Coyne’s review of Darwin Devolves has too little intellectual content to sustain any real engagement.
Writing in the journal Science, reviewers Lents, Swamidass, and Lenski make a very specific, clear, strong, and unambiguous claim.