I think this Dawkinsian GUCN is akin to the particular 'rational' precomittments of a Flat Earth cosmography. In one sense, a Flat Earth cosmography is easily obtained from 'the evidence'---such as gravity and locally extensive flatness. In another sense, a Flat Earth cosmography is endlessly impossible to defend against the broader and deeper evidence---such as geographically and personally bodily local. A Flat Earth cosmography also is a physically and metaphysically unnecessary model of cosmography.
The birds have no need of the particular precomittments of a Flat Earth cosmography. For them, the idea of a globe, and the idea of a macro-mass-related kind of gravity, do just fine. And a Flat Earth cosmography is at once too simplistic and too complicated.