As someone who used to struggle with birds until I got OBSESSED with my Pidgeot and then drew them so much that I got good or at least decent at them I personally treat it similar to the typical muzzle in that it's cause for extension of the face forward a bit. This also allows you to add extra lip expression without it feeling weird. Obviously its more or less realistic depending on the species, but in general I feel like the strat has worked for me.