Watched a Robin feed its mate or its baby. The mate or baby was grey
w/black and white spotted and appeared to have its feathers fluffed
out and sitting quite still in the grass. The Robin would find food
in the grass and give it to the grey spotted one. The grey one did
not hop around at all, but did fly away eventually. They grey bird
had a totally different posture, shape, size and neck.

After looking at photographs of a thrush, the grey bird?, does look similiar.