Homogenous granular media composed of spherocylindrical rods rearrange and order vertically upon vibration. Performing pseudo-bidimensional experiments and simulations, we isolated void-filling mechanism as a cause for this phenomenon, independently of wall influence. Our discrete element model (DEM) faithfully captures the physical behavior. Simulating the segregation of a mixture of spheres and spherocylinders of same volume, which is vibrated in a cylinder, we observe spherocylinder migration either to the top or to the bottom of the bed depending on particle elongation. This phenomenon is linked to the rod verticalisation and is also interpreted through an extension of the void-filling mechanism.