I don't know that it happens from shipping but, it seems like everyday  someone mentions a bird walking backwards, or doing sommersaults,  and most often it is a SILKY.  Silkies are extremely popular so that may account for the sheer number of reports.  I expect people will be labeling it as "silky syndrome" some  day soon.  It seems to be most prevalent in breeds with vaulted skulls. I recall someone posted actual xrays of a silky skull or link to it and it showed there was just the layer of skin - no boney structure covering the brain.  They are very  prone to head injuries from bumps or pecking.  Not all silkies have this problem.  Sometimes it is a cochin or other breed. It is especially sad since they are such a sweet breed.