actually the feathers are heavier because you have 50kg of each but 50kg of feathers will form at least two birds through evolution and birds are heavier than feathers so feathers win
kg is mass; thus, the way the pile is distributed does affect the weight of it. though they're probably both compacted into a box of some sort - the feather box will be a lot larger and thus easier to pick up at one end, but dead lifting both will be equivalently hard, assuming the box size itself isn't cumbersome
